Merge branch 'feat/go-m6-7-embed-verify'

Reviewed-on: #35

CHANGELOG.md

@@ -1,5 +1,239 @@
 # Changelog
 
+## 2026-05-11 23:58 CEST — fix(reconcile): fill earliest month deficit first in multi-month allocations
+
+- Multi-month payment allocation now fills the earliest in-window deficit first and spills
+  any remainder to later months, accounting for prior transactions' contributions to each month.
+  Previously a single transaction was split proportionally to each month's total expected fee,
+  ignoring what earlier transactions had already paid — surfaced by Matyáš Thér's 200+550 case
+  showing 566/183 instead of 500/250.
+- Files: `scripts/match_payments.py`, `go/internal/domain/reconcile/reconcile.go`, tests, parity fixtures.
+
+## 2026-05-11 22:56 CEST — fix(python): parse Fio 2-digit-year dates + add `make sync-debug` dry-run tool
+
+- Fix: `scripts/fio_utils.py` `parse_czech_date` now accepts `DD.MM.YY` / `D.M.YY` in addition to the 4-digit-year variants. Fio's transparent page now mixes both forms in the same response; the 2-digit rows were being silently dropped, which caused `make sync-2026` to miss every recent transfer. Mirrors the Go-side fix from 2026-05-07 (CHANGELOG entry below).
+- Added `--dry-run` and `--print-fio-table` flags to `scripts/sync_fio_to_sheets.py`, plus a `make sync-debug [DAYS=N]` Makefile target. Mirrors `make go-sync-debug`: fetches from Fio and dedupes against the sheet, prints `STATUS=NEW/DUP` per transaction, and prints per-row `Dry run: would append …` lines + `would sort by date` instead of touching the sheet.
+- Added always-on stderr diagnostics in `scripts/fio_utils.py`: which fetcher was selected (authenticated API vs. transparent-page scraper with `FIO_API_TOKEN`-unset warning), and raw-vs-after-filter transaction counts on both paths — so this class of "scraper drops everything" bug surfaces immediately.
+## 2026-05-08 15:24 CEST — feat(go): M6.7 — single-binary embed verification
+
+- Confirmed `embed.FS` wiring is complete: templates parsed via `template.ParseFS(templateFS, ...)`, static assets served via `http.FileServerFS(fs.Sub(staticFS, "static"))`.
+- Added `go/internal/web/assets_test.go` with two tests: `TestEmbedCompleteness` (walks disk vs embed.FS to catch forgotten files) and `TestStaticAssetsServed` (hits `/static/css/app.css` and all JS files through the mux, asserts 200 + Content-Type + non-empty body + 404 for unknown paths).
+- Closes M6; single binary confirmed self-contained with no adjacent `templates/` or `static/` required at runtime.
+- Key files: `go/internal/web/assets_test.go` (new).
+
+## 2026-05-08 14:55 CEST — feat(go): M6.6.1 — Pay-button QR popup modal
+
+- Restored the Python `showPayQR` in-page modal UX that was lost in M6.6 (Pay buttons were navigating the tab to the raw `/qr` PNG).
+- Replaced `<a href="{{qrHref ...}}">Pay</a>` with `<button data-name|amount|month|raw-month>` on `/adults` and `/juniors`; click is handled by a new `static/js/payment-qr.js` IIFE module that opens `#qrModal` with title, account, amount, message, and the QR image.
+- Added `#qrModal` markup to both templates; CSS `display:none` / `.active{display:flex}` rules added (content rules were already present from M6.1). `Esc`, `[close]`, and outside-click all dismiss; coexists with the M6.5 member-detail modal.
+- Removed the now-dead `qrHref` / `qrHrefAll` template helpers from `render.go`.
+- Markup tests in `html_handler_test.go` assert modal IDs, script tag, `data-bank-account`, and that no bare `href="/qr"` links remain.
+- Key files: `go/internal/web/static/js/payment-qr.js`, `go/internal/web/templates/adults.tmpl`, `go/internal/web/templates/juniors.tmpl`, `go/internal/web/render.go`, `go/internal/web/static/css/app.css`.
+
+## 2026-05-08 13:57 CEST — feat(go): M6.6 — /qr, /sync-bank, /flush-cache, /version
+
+- Added `GET /qr`: generates Czech QR Platba PNG from SPD payload (account, amount, message query params); ports Python's `qr_code()` handler exactly including account validation, amount clamping, and `*` stripping.
+- Implemented `GET /sync-bank`: runs Fio sync → infer payments → cache flush, captures output into `sync.tmpl` page with success/error banner.
+- Implemented `GET /flush-cache` + `POST /flush-cache`: form + action that deletes cache files and shows deleted count.
+- Added `GET /version` as a JSON alias of `GET /api/version` (Python parity).
+- Added `FlushCache() (int, error)` to `membership.Sources` interface; implemented on `realSources` via `cache.FileCache.Flush()`.
+- Introduced `web.ActionHandlers{BankSync}` — closure-based dep injection for sync, constructed in `serverCmd` with fio + sheets clients.
+- New dependency: `github.com/skip2/go-qrcode`.
+- Key files: `go/internal/web/qr.go`, `go/internal/web/html_handler.go`, `go/internal/web/server.go`, `go/internal/services/membership/loader.go`, `go/internal/web/templates/sync.tmpl`, `go/internal/web/templates/flush_cache.tmpl`.
+
+## 2026-05-08 13:19 CEST — feat(go): M6.5 — member-detail modal JS module
+
+- Added `static/js/member-detail.js`: fetches `/api/adults` or `/api/juniors` once on page load, caches the response, renders a per-member detail modal on `[i]` row click.
+- Modal sections: status-per-month table, fee exceptions, other transactions, matched payment history, toggleable raw-payments debug view.
+- Keyboard nav: `Esc` closes, `↑`/`↓` walk visible (name-filtered) rows; click outside modal content closes it.
+- Added `[i]` info icon and `#memberModal` markup to `adults.tmpl` and `juniors.tmpl`; all CSS was already in place from M6.1.
+- Added `TestModalMarkup` assertions to `html_handler_test.go`.
+
+## 2026-05-08 12:48 CEST — feat(go): M6.4 — Go-native /payments page
+
+- Extracted `AssemblePayments(ctx)` from the inlined JSON handler body, following the M6.2/M6.3 `AssembleAdults`/`AssembleJuniors` pattern.
+- Added `PaymentsPageData` to `render.go`; wired `HTMLHandler.ServePayments` to call `AssemblePayments` and render the new template.
+- Replaced the "Coming in M6.4" placeholder in `payments.tmpl` with the full grouped-by-person ledger: alphabetical `<h2>` member blocks, each with a `txn-table` (Date / Amount / Purpose / Bank Message), newest-first rows, `"Unmatched / Unknown"` bucket.
+- Appended ledger CSS classes to `app.css` (`.ledger-container`, `.member-block`, `.txn-table`, `.txn-{date,amount,purpose,message}`, `tr:hover`).
+- Added `TestPaymentsPage` markup test. No filters, no JS — matches the Python page.
+
+## 2026-05-08 11:25 CEST — feat(go): M6.3 — Go-native /juniors page
+
+- Extracted `AssembleJuniors(ctx)` from the JSON handler so HTML and JSON share one view-model path (mirrors `AssembleAdults`).
+- Added `JuniorsPageData` to `render.go`; wired `HTMLHandler.ServeJuniors` to call `AssembleJuniors` and render the new template.
+- Replaced the 4-line "Coming in M6.3" placeholder in `juniors.tmpl` with the full template: member table, name/month-range filters, totals row, Credits + Debts sections, Pay / Pay All links to `/qr`. No Unmatched section (parity with Python).
+- J/A attendance breakdown and `"?"` sentinel rendered via `MonthCell.Text` produced by `buildJuniorMemberRow` — no extra template logic.
+- `make parity` reports 3/3 routes OK; all Go tests pass.
+
+## 2026-05-08 11:11 CEST — fix: period selector showed only Dec 2025+ on adults
+
+- Restored the `2025-09 → 2025-10` adult merge in `scripts/attendance.py` and `go/internal/services/membership/sources.go` (commented-out by `1257f0d`); the `2025-12 → 2026-01` mapping stays disabled per product decision (Dec and Jan are billed separately for adults).
+- Dropped the `defaultFrom = maxMonthIdx − 4` JS auto-default in `templates/adults.html` and `templates/juniors.html` (introduced by `7774301`); the From-selector now starts at the oldest available month so all non-future periods render on first load. Future-month removal is preserved.
+- `go/internal/services/membership/sources_test.go`: `TestLoadAdults` / `TestLoadAdults_Fee` now assert that Sep dates land in the merged `2025-10` bucket.
+- **Independent of these code changes**: the live adults attendance Google Sheet header had been pruned to start at `02.12.2025` (Sep/Oct/Nov 2025 columns deleted); restoring those columns from Sheets version history is required to actually see those periods on the dashboard.
+
+## 2026-05-08 10:15 CEST — fix(go): adults template — use lifted CSS classes for visual parity
+
+- Use existing `.balance-pos` / `.balance-neg` (drop invented `balance-cell` / `balance-negative`); Pay-All button now lives inside the balance cell with `position: relative` (matches Python; no separate trailing column).
+- Credits / Debts / Unmatched sections rewritten from `<ul>` / `<table>` to `<div class="list-container"><div class="list-item">…` / `<div class="unmatched-row">…` so the lifted CSS actually applies.
+- Section headings get the descriptive Python text: "Credits (Advance Payments / Surplus)", "Debts (Missing Payments)".
+- Source links moved from page bottom to a `<div class="description">` block under the h1, matching Python's "Source: Attendance Sheet | Payments Ledger".
+- Total row uses `cell-{{Status}}` plus the small "received / expected" caption span and Python's inline-styled bold/dark background.
+- Drop the redundant `class="cell"` wrapper; debts amount turns red via inline style; balance value drops the trailing "CZK".
+
+## 2026-05-08 01:09 CEST — feat(go): M6.2 — adults page (table, filters, Pay buttons)
+
+- `go/internal/web/api/handler.go`: extracted `ServeAdults` body into `AssembleAdults(ctx)` — shared by the JSON API route and the new HTML handler.
+- `go/internal/web/render.go`: added `AdultsPageData` view model (`PageData` + `api.AdultsResponse` + `Error`); `tmplFuncs` with `qrHref` / `qrHrefAll` (URL-encode QR Platba params, convert YYYY-MM → MM/YYYY).
+- `go/internal/web/html_handler.go`: `HTMLHandler` gains `*api.Handler`; `ServeAdults` loads real reconcile data and renders the full adults page.
+- `go/internal/web/templates/adults.tmpl`: full table (per-member rows, per-cell status classes, `data-month-idx`, Pay button hrefs to `/qr`), totals row, credits/debts/unmatched sections, filter controls, sheet links.
+- `go/internal/web/static/js/filters.js`: name filter (NFD-normalize) + month-range hide/show by `data-month-idx`; future months hidden by default.
+
+## 2026-05-08 00:44 CEST — feat(go): M6.1 — template skeleton + embed.FS
+
+- `go/internal/web/templates/`: `base.tmpl` (full HTML layout), `partials/nav.tmpl` (three-tier nav with active-link highlighting), `partials/footer.tmpl` (build meta), and stub pages for each route (adults/juniors/payments/sync/flush_cache).
+- `go/internal/web/static/css/app.css`: terminal-green-on-black theme extracted once from Python `templates/adults.html` — shared by all Go HTML pages via `<link>`.
+- `go/internal/web/assets.go`: `//go:embed templates static` for single-binary deployment.
+- `go/internal/web/render.go`: `Renderer` parses a fresh `*template.Template` per page at startup; `Render(w, name, data)` executes the "base" template block.
+- `go/internal/web/html_handler.go`: `HTMLHandler` with one method per route (`ServeAdults`, `ServeJuniors`, `ServePayments`, `ServeSync`, `ServeFlushCache`).
+- `go/internal/web/server.go`: drops `helloHandler`; `GET /{$}` now redirects to `/adults`; HTML + `/static/` routes registered alongside the existing `/api/*` routes.
+- `go/internal/web/html_handler_test.go`: smoke test — each route returns 200 `text/html` with exactly one `class="active"` on the matching nav link.
+
+## 2026-05-08 00:26 CEST — fix(py): parity coercions — amount/message types + junior '?' sticky
+
+- `scripts/match_payments.py`: added `get_float` helper — non-numeric `amount` values (e.g. `"---"` placeholder rows) now coerce to `0.0` matching Go's `parseFloat` behaviour; `message` field now goes through `get_str` so numeric cell values (bank references) are emitted as strings, matching Go's `fmt.Sprint`.
+- `scripts/views.py`: junior month cell `"?"` text is now sticky across exception overrides. Previously `reconcile` replaced `expected` with the exception amount before the view builder ran, silently turning `"?"` into `"-"` when the override was 0. Fixed by deriving `is_unknown` from `original_expected == "?"` instead of `expected == "?"`. Also aligned tooltip guard: only show Received/Expected for non-unknown months (or when paid > 0), matching Go's `!md.IsUnknown` condition.
+
+## 2026-05-07 23:51 CEST — feat(py): M5.4 fix #2 — add vs and sync_id to payments tx projection
+
+- `scripts/match_payments.py`: `fetch_sheet_data` now reads `VS` and `Sync ID` columns and includes `vs`/`sync_id` keys in every tx dict. Previously only 9 columns were projected, causing `make parity` to report extra `vs`/`sync_id` fields on every raw payment row emitted by the Go backend. Values flow through `group_payments_by_person` → `_unwrap_view_model_for_api` to `raw_payments` (adults/juniors) and `grouped_payments` (payments) automatically.
+- `tests/test_app.py`: updated `/api/*` mock fixtures to include `vs`/`sync_id` keys for realism.
+- **Cache note**: after deploying, hit `POST /flush-cache` once so the in-process cache is cleared and the next request picks up the new column lookups.
+
+## 2026-05-07 23:37 CEST — fix(go): accept single-digit day/month in attendance date headers
+
+- `go/internal/services/membership/sources.go`: `parseDates` now uses Go time formats `2.1.2006` and `1/2/2006` (single-digit reference forms, which accept both padded and unpadded inputs) instead of `02.01.2006` and `01/02/2006`. The Czech attendance sheet headers contain dates like `1.6.2026`, `23.3.2026`, `6.4.2026` — Go silently dropped those columns under the strict zero-padded format, while Python's `strptime("%d.%m.%Y")` accepted them. Effect was a missing `2026-06` month entirely on `/api/juniors` plus undercounted attendance for any month with single-digit columns; both surfaced as diffs in `make parity`.
+- `sources_test.go::TestParseDates_SingleDigitDayMonth` added as a regression guard covering both Czech and US format flavours with and without leading zeros.
+
+## 2026-05-07 23:17 CEST — fix(go): pass raw value to FormatDate so numeric serial-day dates format
+
+- `go/internal/services/membership/sources.go`: transaction-row parser now passes `row[idxDate]` directly to `matching.FormatDate` (via a new `getRaw` helper) instead of stringifying first via `getVal`. The Sheets API returns numeric serial-day values as `float64` for date-formatted cells; pre-stringifying them defeated `FormatDate`'s `case float64:` dispatch, causing all numeric dates to leak through as `"46147"` style strings instead of `"2026-05-05"`.
+- Surfaced by `make parity` (M5.4): every `transactions[].date` field on `/api/adults` and `/api/juniors` differed between Python and Go.
+- `sources_test.go::TestLoadTransactions` extended with a numeric-serial-day row covering the regression.
+
+## 2026-05-07 23:05 CEST — fix(go): default CacheDir to `tmp/go` to avoid Python collision
+
+- `go/internal/config/config.go`: `CacheDir` default changed from `tmp` to `tmp/go`. Override via `CACHE_DIR` env var still works.
+- Why: both backends used `tmp/<key>_cache.json` with the same keys (`attendance_regular`, `attendance_juniors`, `payments_transactions`, `exceptions_dict`) but different shapes — Python caches post-processed view-model tuples, Go caches raw rows. Whichever wrote last poisoned the cache; running both in parallel produced `ValueError: too many values to unpack (expected 2, got 68)` on Python's `/adults` after the Go server populated `attendance_regular_cache.json` with raw CSV rows.
+- After upgrading: stop the Go server, hit `/flush-cache` on the Python side once (rewrites `tmp/*.json` with correct shapes), then restart `make web-go` — it will use `tmp/go/` going forward. Required for the M5.4 `make parity` workflow which assumes both backends run side-by-side.
+
+## 2026-05-07 22:55 CEST — feat(go): M5.4 — parity diff binary + `make parity`
+
+- `go/cmd/parity/main.go`: new standalone binary that GETs `/api/adults`, `/api/juniors`, `/api/payments` from both Python (:5001) and Go (:8080) backends, scrubs an allowlist (`render_time.total`), and prints `cmp.Diff` for any remaining differences. Exits 0 on full match, 1 on diffs, 2 on fetch/parse errors — CI-friendly for M7.2. `/api/version` is excluded by design (returns binary identity — tag/commit/build_date — which differs between independently built backends); still accessible via `make parity ARGS="-route /api/version"`.
+- `go/cmd/parity/scrub_test.go`: 4 unit tests covering top-level delete, nested delete, missing path, and non-map parent.
+- `go/go.mod`: `github.com/google/go-cmp` promoted to direct dependency.
+- `Makefile`: `parity` target added (`.PHONY`, help, `cd go && go run ./cmd/parity`).
+- `docs/plans/2026-05-07-2254-m5-4-parity-binary.md`: plan archived.
+
+## 2026-05-07 22:37 CEST — feat(py): M5.3 — Python /api/* shadow endpoints
+
+- `app.py`: four new JSON routes (`/api/version`, `/api/adults`, `/api/juniors`, `/api/payments`) mirroring the Go `/api/*` handlers; `_unwrap_view_model_for_api()` helper expands pre-serialised JSON strings and renames `month_labels_json` → `month_labels`, `raw_payments_json` → `raw_payments` to match Go wire contract.
+- `tests/test_app.py`: four new smoke tests asserting top-level key sets and that unwrapped fields are objects (not strings).
+
+## 2026-05-07 20:13 CEST — feat(go): M5.2 — HTTP handlers for /api/adults, /api/juniors, /api/payments, /api/version
+
+- `web/api/handler.go`: `Handler` struct + `ServeAdults`, `ServeJuniors`, `ServePayments`, `ServeVersion` using `membership.Sources`.
+- `web/api/build_{adults,juniors,payments,common}.go`: ports of `scripts/views.py` view-model builders; `buildJuniorMemberRow` handles `"?"` sentinel, `:NJ,MA` breakdown, unknown-month skip.
+- Extended `reconcile.FeeData`/`MonthData` with `IsUnknown`, `JuniorAttendance`, `AdultAttendance`; `Transaction` with `ManualFix`, `VS`, `BankID`, `SyncID`.
+- `sources.go` exports `AdultMergedMonths`/`JuniorMergedMonths`; parses new FeeData and transaction columns.
+- `web/server.go` + `cmd/fuj/main.go` wired to register `/api/*` routes.
+- PR #17.
+
+## 2026-05-07 17:37 CEST — feat(go): M5.1 — /api/* wire types + JSON Schemas
+
+- New `go/internal/web/api/` package: `AdultsResponse`, `JuniorsResponse`, `PaymentsResponse`, `VersionResponse` with explicit `json:` tags matching Python view-model keys.
+- `Expected{Value int; Unknown bool}` custom `MarshalJSON` emits integer or `"?"` for junior single-attendance months.
+- `schemagen_test.go` golden-tests four JSON Schemas committed to `go/tests/fixtures/api-schema/`. `JSONSchema()` on `Expected` lives in the test file — production binary has no jsonschema dep.
+- PR #16.
+
+## 2026-05-07 15:26 CEST — refactor(app): extract view-model builders into scripts/views.py
+
+- Pulled ~350 lines of inline per-row computation out of `adults_view`, `juniors_view`, and `payments` into three pure functions in `scripts/views.py`: `build_adults_view_model`, `build_juniors_view_model`, `build_payments_view_model`.
+- Moved `get_month_labels`, `group_payments_by_person`, `adapt_junior_members` from `app.py` to `scripts/views.py`. Route handlers now ~25 lines each.
+- Hotfixed missing `import re` that caused 500 on `/qr` after the refactor.
+- No behaviour change; all 27 tests pass. Prep for `/api/*` shadow endpoints (M5).
+
+## 2026-05-07 14:13 CEST — feat(go): --print-fio-table + Fio debug logging + date parser fix
+
+- Added `--print-fio-table` flag to `fuj sync --dry-run`: prints an aligned table of every Fio transaction in the window with `STATUS=NEW/DUP`, using `text/tabwriter`. Key files: `go/internal/services/banksync/fio_table.go`, `sync.go`, `cmd/fuj/main.go`.
+- Added `LOG_LEVEL=DEBUG` debug logging on the Fio fetch path: client variant selected, full GET URL (token redacted on API path), HTTP status, body bytes, and per-parse drop-reason counters (`raw_rows`, `kept`, `dropped_bad_date`, `dropped_nonpositive_amount`). Key files: `go/internal/io/fio/{client,api,transparent}.go`.
+- Fixed `parseCzechDate` to accept `DD.MM.YY` (2-digit year) in addition to the 4-digit variant — Fio's transparent page now serves this format. Key file: `go/internal/io/fio/transparent.go`.
+- Added `make go-sync-debug [DAYS=N]` Makefile target (default 30 days).
+
+## 2026-05-07 10:32 CEST — feat(go): --dry-run for fuj sync
+
+- `SyncOpts.DryRun bool` added; when true, `SyncToSheets` prints planned writes (`would write header row`, `would append date=… amount=… sender=…`, `would sort by date`) and returns without calling `WriteHeader`, `AppendValues`, or `SortByDateColumn`.
+- `fuj sync --dry-run` flag wired in `cmd/fuj/main.go`; mirrors existing `fuj infer --dry-run` behaviour.
+- `TestSyncToSheets_DryRun` added to banksync test suite.
+
+## 2026-05-07 01:03 CEST — feat(go/M4): IO layer behind interfaces
+
+- `go/internal/io/attendance`: CSV-over-public-URL client + `Fake` for both adult and junior tabs.
+- `go/internal/io/drive`: thin Drive v3 wrapper for `modifiedTime` reads + `Fake`.
+- `go/internal/io/sheets`: Sheets v4 client (`GetValues`, `AppendValues`, `BatchUpdateValues`, `WriteHeader`, `SortByDateColumn`) + `Fake` with call-capture for assertions.
+- `go/internal/io/cache`: Drive-modifiedTime-gated `FileCache` with two TTL knobs, atomic writes, and generic `Get[T]`; Python-compatible JSON format; `Flush()` support.
+- `go/internal/io/fio`: `Client` interface backed by Fio REST API (`apiClient`) and HTML-scraper (`transparentClient`); `Fake` for tests. Fixtures in `testdata/`.
+- `go/internal/services/membership/sources.go`: `NewSources` wires attendance CSV + Sheets + cache into `LoadAdults`, `LoadJuniors`, `LoadTransactions`, `LoadExceptions`. Includes Czech month/merged-month parsing logic.
+- `go/internal/services/banksync`: `SyncToSheets` (dedup via SHA-256 Sync ID, optional sort) and `InferPayments` (name-match + `[?]` review prefix, dry-run) — fully tested with fakes.
+- `go/cmd/fuj/main.go`: `sync` and `infer` subcommands wired to real clients; `fees` and `reconcile` now use real `NewSources`.
+- All packages lint-clean (golangci-lint v1.64.8, gofumpt extra-rules).
+
+## 2026-05-06 23:25 CEST — feat(go/M3): fixture capture + parity test framework
+
+- `scripts/capture_fixtures.py`: dispatcher CLI that calls each ported function with seeded inputs and emits captured output as JSON fixtures.
+- `scripts/scrub_fixtures.py`: deterministic PII scrubber (SHA-256 pseudonyms, digit-preserving account/VS hashes, name-sweep in free text).
+- `scripts/_fixture_seeds.py`: handcrafted seed registry for all 10 pure functions + 10 reconcile branch-coverage cases.
+- 98 fixture files committed under `go/tests/fixtures/pure/<func>/` and `go/tests/fixtures/reconcile/`; all PII-free.
+- `go/tests/parity/parityio.go`: shared loader with generic `LoadDir`/`RunAll` helpers and typed `In`/`Out` structs for all 10 functions.
+- 11 parity test packages under `//go:build parity`: 10 pure-function tests + bespoke reconcile test with per-cell float tolerance.
+- Makefile: `go-parity`, `go-test-all`, `capture-fixtures` targets.
+- `go/tests/fixtures/README.md`: refresh workflow, PII audit guide, adding-a-fixture steps.
+
+## 2026-05-06 17:49 CEST — feat(go/M2.11-12): wire fuj fees + fuj reconcile subcommands
+
+- New `go/internal/services/membership` package: `AttendanceLoader`, `TransactionLoader`, `ExceptionLoader` interfaces, a stub (`NewStubSources`) that returns `ErrIOPending`, and `FeesReport` / `ReconcileReport` orchestration functions backed by real `domain/fees` + `domain/reconcile` logic.
+- Text formatters `printFeesTable` / `printReconcileReport` port the output of `calculate_fees.py` and `match_payments.py print_report` verbatim.
+- `cmd/fuj/main.go`: `fuj fees` and `fuj reconcile` subcommands now dispatch properly; `fuj sync` / `fuj infer` retain the [M4] placeholder.
+- Both subcommands exit 1 with a clean `"io layer not yet wired up; lands in milestone M4"` message until real Sheets loaders are injected in M4.
+- 13 unit tests covering stubs, all formatter branches (OK/partial/UNPAID/dash cells, credits, debts, unmatched, review annotation), and orchestration wiring via fake loaders.
+
+## 2026-05-06 16:38 CEST — fix: include juniors in payment-inference roster
+
+- `scripts/infer_payments.py`: union adults + junior rosters so junior-only members are visible to the matcher.
+- Root cause: `get_members_with_fees()` reads only the adults sheet; junior-only kids like Jáchym Kubík were absent from `member_names`, causing the exact-match short-circuit to never fire and a different adult sharing the first name to win via fuzzy review.
+- Two regression tests added to `tests/test_match_members.py`.
+
+## 2026-05-06 16:05 CEST — feat(go/M2.10): port domain/reconcile.Reconcile
+
+- New `go/internal/domain/reconcile` package porting the three-phase payment allocation from `scripts/match_payments.py reconcile()`.
+- 12 unit tests covering all Python test cases plus Go-only extras (diacritics tolerance, `[?]` stripping, `other:` purpose, out-of-window credit, inference fallback, unmatched, no-transaction guard).
+
+## 2026-05-06 13:18 CEST — feat(go/M2.7-2.9): port domain/matching package
+
+- New `go/internal/domain/matching` package porting three helpers from `scripts/match_payments.py`.
+- `BuildNameVariants` — extracts normalized ASCII search variants from a member name, including nickname (from parens) and separate first/last; filters variants shorter than 3 chars; `variants[0]` is always the full normalized base name.
+- `MatchMembers` — finds members in free text with `"auto"` or `"review"` confidence; exact-name short-circuit prevents nickname substrings (e.g. `tov`) from matching inside surnames (e.g. `ottova`).
+- `FormatDate` — normalizes Google Sheets date values: handles nil, empty, int/float64 serial-days since 1899-12-30 (supports fractional serials), pre-formatted `YYYY-MM-DD` strings, and garbage input — never errors.
+- `InferTransactionDetails` — composes name + month matching over sender/message/user_id; falls back to sender-only member match and date-derived month when text gives no signal.
+- 21 table-driven tests; all expected values verified against live Python on 2026-05-06.
+
+## 2026-05-06 12:43 CEST — feat(go/M2.6): port domain/synch.GenerateSyncID
+
+- New `go/internal/domain/synch` package with `GenerateSyncID(Transaction) string` ported from `scripts/sync_fio_to_sheets.py` `generate_sync_id`.
+- Byte-stable SHA-256 hash over `date|amount|currency|sender|vs|message|bank_id` (lowercased, UTF-8); `Currency: ""` defaults to `"CZK"` matching the Python missing-key fallback.
+- Key subtlety: Python's `str(float)` emits `"500.0"` for whole-valued floats and switches to scientific notation at `|f| >= 1e16` or `|f| < 1e-4` — replicated in `formatAmount` using `'f'`/`'e'` format selection.
+- 6 table-driven hash tests + 9 `formatAmount` tests; all expected values verified against live Python on 2026-05-06.
+
 ## 2026-05-06 09:38 CEST — feat(go/M2.5): port domain/money.ParseCZK
 
 - New `go/internal/domain/money` package with `ParseCZK(string) (float64, error)` ported from `scripts/infer_payments.py` `parse_czk_amount`.

Makefile

@@ -1,4 +1,4 @@
-.PHONY: help fees match web web-py web-debug web-go go-build go-test go-run go-lint image run sync sync-2026 test test-v docs
+.PHONY: help fees match web web-py web-debug web-go go-build go-test go-test-all go-parity go-run go-sync-debug go-lint capture-fixtures parity image run sync sync-2026 test test-v docs
 
 export PYTHONPATH := scripts:$(PYTHONPATH)
 VENV := .venv
@@ -23,13 +23,19 @@ help:
 	@echo "  make web-go      - Build and start Go dashboard on :8080"
 	@echo "  make web-debug   - Start Python dashboard in debug mode"
 	@echo "  make go-build    - Build Go binary to bin/fuj"
-	@echo "  make go-test     - Run Go tests"
+	@echo "  make go-test     - Run Go unit tests"
+	@echo "  make go-parity   - Run Go parity tests (requires -tags=parity fixture corpus)"
+	@echo "  make go-test-all - Run both unit and parity tests"
 	@echo "  make go-lint     - Run golangci-lint on Go code"
+	@echo "  make go-sync-debug [DAYS=N] - Dry-run Go sync with Fio debug logs and txn table (default DAYS=30)"
+	@echo "  make capture-fixtures - Regenerate parity fixture corpus from live Python"
+	@echo "  make parity      - Diff /api/* between web-py (:5001) and web-go (:8080); both must be running"
 	@echo "  make image       - Build Python OCI container image"
 	@echo "  make run         - Run the built Python Docker image locally"
 	@echo "  make sync        - Sync Fio transactions to Google Sheets"
 	@echo "  make sync-2025   - Sync Fio transactions for Q4 2025 (Oct-Dec)"
 	@echo "  make sync-2026   - Sync Fio transactions for the whole year of 2026"
+	@echo "  make sync-debug [DAYS=N] - Dry-run Python sync with Fio diagnostics and txn table (default DAYS=30)"
 	@echo "  make infer       - Infer payment details (Person, Purpose, Amount) in the sheet"
 	@echo "  make reconcile   - Show balance report using Google Sheets data"
 	@echo "  make venv        - Sync virtual environment with pyproject.toml"
@@ -64,15 +70,43 @@ go-build:
 go-test:
 	cd $(GO_SRC) && go test -race ./...
 
+go-parity:
+	cd $(GO_SRC) && go test -tags=parity ./tests/parity/...
+
+go-test-all: go-test go-parity
+
+capture-fixtures: $(PYTHON)
+	@echo "Capturing and scrubbing fixtures for all registered functions..."
+	@for func in normalize parse_month_references calculate_fee calculate_junior_fee \
+	              parse_czk_amount generate_sync_id build_name_variants match_members \
+	              infer_transaction_details format_date reconcile; do \
+	    dir="go/tests/fixtures/$$([[ $$func == reconcile ]] && echo reconcile || echo pure/$$func)"; \
+	    mkdir -p "$$dir"; \
+	    PYTHONPATH=scripts:. $(PYTHON) scripts/capture_fixtures.py --func $$func --all \
+	    | while IFS= read -r line; do \
+	        case_id=$$(echo "$$line" | $(PYTHON) -c "import sys,json; print(json.load(sys.stdin)['case'])"); \
+	        echo "$$line" | $(PYTHON) scripts/scrub_fixtures.py > "$$dir/$${case_id}.json"; \
+	    done; \
+	    echo "  $$func done"; \
+	done
+	@echo "capture-fixtures complete."
+
 go-run: go-build
 	./$(GO_BIN) $(ARGS)
 
+DAYS ?= 30
+go-sync-debug: go-build
+	LOG_LEVEL=DEBUG ./$(GO_BIN) sync -dry-run -print-fio-table -days $(DAYS)
+
 go-lint:
 	cd $(GO_SRC) && golangci-lint run ./...
 
 web-go: go-build
 	./$(GO_BIN) server
 
+parity:
+	cd $(GO_SRC) && go run ./cmd/parity $(ARGS)
+
 image:
 	docker build -t fuj-management:latest \
 		--build-arg GIT_TAG=$$(git describe --tags --always 2>/dev/null || echo "untagged") \
@@ -92,6 +126,9 @@ sync-2025: $(PYTHON)
 sync-2026: $(PYTHON)
 	$(PYTHON) scripts/sync_fio_to_sheets.py --credentials .secret/fuj-management-bot-credentials.json --from 2026-01-01 --to 2026-12-31 --sort-by-date
 
+sync-debug: $(PYTHON)  ## Dry-run Python sync with Fio diagnostics and txn table (default DAYS=30)
+	$(PYTHON) scripts/sync_fio_to_sheets.py --credentials .secret/fuj-management-bot-credentials.json --days $(DAYS) --dry-run --print-fio-table
+
 infer: $(PYTHON)
 	$(PYTHON) scripts/infer_payments.py --credentials $(CREDENTIALS)
 

app.py

@@ -7,7 +7,7 @@ import os
 import io
 import qrcode
 import logging
-from flask import Flask, render_template, g, send_file, request
+from flask import Flask, render_template, g, send_file, request, jsonify
 
 # Configure logging, allowing override via LOG_LEVEL environment variable
 log_level = os.environ.get("LOG_LEVEL", "INFO").upper()
@@ -21,8 +21,14 @@ from config import (
     ATTENDANCE_SHEET_ID, PAYMENTS_SHEET_ID, JUNIOR_SHEET_GID,
     BANK_ACCOUNT, CREDENTIALS_PATH,
 )
-from attendance import get_members_with_fees, get_junior_members_with_fees, ADULT_MERGED_MONTHS, JUNIOR_MERGED_MONTHS
-from match_payments import reconcile, fetch_sheet_data, fetch_exceptions, normalize, canonical_member_key
+from attendance import get_members_with_fees, get_junior_members_with_fees
+from match_payments import reconcile, fetch_sheet_data, fetch_exceptions
+from views import (
+    build_adults_view_model,
+    build_juniors_view_model,
+    build_payments_view_model,
+    adapt_junior_members,
+)
 from cache_utils import get_sheet_modified_time, read_cache, write_cache, _LAST_CHECKED, flush_cache
 from sync_fio_to_sheets import sync_to_sheets
 from infer_payments import infer_payments
@@ -38,44 +44,6 @@ def get_cached_data(cache_key, sheet_id, fetch_func, *args, serialize=None, dese
         write_cache(cache_key, mod_time, serialize(data) if serialize else data)
     return data
 
-def get_month_labels(sorted_months, merged_months):
-    labels = {}
-    for m in sorted_months:
-        dt = datetime.strptime(m, "%Y-%m")
-        # Find which months were merged into m (e.g. 2026-01 is merged into 2026-02)
-        merged_in = sorted([k for k, v in merged_months.items() if v == m])
-        if merged_in:
-            all_dts = [datetime.strptime(x, "%Y-%m") for x in sorted(merged_in + [m])]
-            years = {d.year for d in all_dts}
-            if len(years) > 1:
-                parts = [d.strftime("%b %Y") for d in all_dts]
-                labels[m] = "+".join(parts)
-            else:
-                parts = [d.strftime("%b") for d in all_dts]
-                labels[m] = f"{'+'.join(parts)} {dt.strftime('%Y')}"
-        else:
-            labels[m] = dt.strftime("%b %Y")
-    return labels
-
-def group_payments_by_person(transactions, member_names=None):
-    canonical_by_key = (
-        {canonical_member_key(n): n for n in member_names} if member_names else {}
-    )
-    grouped = {}
-    for tx in transactions:
-        person = str(tx.get("person", "")).strip()
-        if not person:
-            continue
-        for p in person.split(","):
-            p = re.sub(r"\[\?\]\s*", "", p).strip()
-            if not p:
-                continue
-            key = canonical_by_key.get(canonical_member_key(p), p)
-            grouped.setdefault(key, []).append(tx)
-    for rows in grouped.values():
-        rows.sort(key=lambda t: str(t.get("date", "")), reverse=True)
-    return grouped
-
 def warmup_cache():
     """Pre-fetch all cached data so first request is fast."""
     logger = logging.getLogger(__name__)
@@ -100,6 +68,16 @@ BUILD_META = _json.loads(_meta_path.read_text()) if _meta_path.exists() else {
     "tag": "dev", "commit": "local", "build_date": ""
 }
 
+
+def _unwrap_view_model_for_api(vm: dict) -> dict:
+    """Expand pre-stringified JSON fields and rename to match Go API contract."""
+    out = dict(vm)
+    out["member_data"] = _json.loads(out.pop("member_data"))
+    out["month_labels"] = _json.loads(out.pop("month_labels_json"))
+    out["raw_payments"] = _json.loads(out.pop("raw_payments_json"))
+    return out
+
+
 warmup_cache()
 
 @app.before_request
@@ -176,386 +154,151 @@ def sync_bank():
 def version():
     return BUILD_META
 
+@app.route("/api/version")
+def api_version():
+    return jsonify(BUILD_META)
+
+@app.route("/api/adults")
+def api_adults():
+    attendance_url = f"https://docs.google.com/spreadsheets/d/{ATTENDANCE_SHEET_ID}/edit"
+    payments_url = f"https://docs.google.com/spreadsheets/d/{PAYMENTS_SHEET_ID}/edit"
+    members_data = get_cached_data("attendance_regular", ATTENDANCE_SHEET_ID, get_members_with_fees)
+    if not members_data:
+        return jsonify({"error": "no data"}), 503
+    members, sorted_months = members_data
+    transactions = get_cached_data("payments_transactions", PAYMENTS_SHEET_ID, fetch_sheet_data, PAYMENTS_SHEET_ID, CREDENTIALS_PATH)
+    exceptions = get_cached_data(
+        "exceptions_dict", PAYMENTS_SHEET_ID, fetch_exceptions,
+        PAYMENTS_SHEET_ID, CREDENTIALS_PATH,
+        serialize=lambda d: [[list(k), v] for k, v in d.items()],
+        deserialize=lambda c: {tuple(k): v for k, v in c},
+    )
+    result = reconcile(members, sorted_months, transactions, exceptions)
+    vm = build_adults_view_model(
+        members, sorted_months, result, transactions,
+        datetime.now().strftime("%Y-%m"),
+        attendance_url=attendance_url, payments_url=payments_url, bank_account=BANK_ACCOUNT,
+    )
+    return jsonify(_unwrap_view_model_for_api(vm))
+
+@app.route("/api/juniors")
+def api_juniors():
+    attendance_url = f"https://docs.google.com/spreadsheets/d/{ATTENDANCE_SHEET_ID}/edit#gid={JUNIOR_SHEET_GID}"
+    payments_url = f"https://docs.google.com/spreadsheets/d/{PAYMENTS_SHEET_ID}/edit"
+    junior_members_data = get_cached_data("attendance_juniors", ATTENDANCE_SHEET_ID, get_junior_members_with_fees)
+    if not junior_members_data:
+        return jsonify({"error": "no data"}), 503
+    junior_members, sorted_months = junior_members_data
+    transactions = get_cached_data("payments_transactions", PAYMENTS_SHEET_ID, fetch_sheet_data, PAYMENTS_SHEET_ID, CREDENTIALS_PATH)
+    exceptions = get_cached_data(
+        "exceptions_dict", PAYMENTS_SHEET_ID, fetch_exceptions,
+        PAYMENTS_SHEET_ID, CREDENTIALS_PATH,
+        serialize=lambda d: [[list(k), v] for k, v in d.items()],
+        deserialize=lambda c: {tuple(k): v for k, v in c},
+    )
+    adapted_members = adapt_junior_members(junior_members)
+    result = reconcile(adapted_members, sorted_months, transactions, exceptions)
+    vm = build_juniors_view_model(
+        junior_members, adapted_members, sorted_months, result, transactions,
+        datetime.now().strftime("%Y-%m"),
+        attendance_url=attendance_url, payments_url=payments_url, bank_account=BANK_ACCOUNT,
+    )
+    return jsonify(_unwrap_view_model_for_api(vm))
+
+@app.route("/api/payments")
+def api_payments():
+    attendance_url = f"https://docs.google.com/spreadsheets/d/{ATTENDANCE_SHEET_ID}/edit"
+    payments_url = f"https://docs.google.com/spreadsheets/d/{PAYMENTS_SHEET_ID}/edit"
+    transactions = get_cached_data("payments_transactions", PAYMENTS_SHEET_ID, fetch_sheet_data, PAYMENTS_SHEET_ID, CREDENTIALS_PATH)
+    adults_data = get_cached_data("attendance_regular", ATTENDANCE_SHEET_ID, get_members_with_fees)
+    juniors_data = get_cached_data("attendance_juniors", ATTENDANCE_SHEET_ID, get_junior_members_with_fees)
+    member_names = []
+    if adults_data:
+        member_names.extend(name for name, _, _ in adults_data[0])
+    if juniors_data:
+        member_names.extend(name for name, _, _ in juniors_data[0])
+    vm = build_payments_view_model(
+        transactions, member_names,
+        attendance_url=attendance_url, payments_url=payments_url,
+    )
+    return jsonify(vm)
+
 @app.route("/adults")
 def adults_view():
     attendance_url = f"https://docs.google.com/spreadsheets/d/{ATTENDANCE_SHEET_ID}/edit"
     payments_url = f"https://docs.google.com/spreadsheets/d/{PAYMENTS_SHEET_ID}/edit"
     credentials_path = CREDENTIALS_PATH
-    
+
     members_data = get_cached_data("attendance_regular", ATTENDANCE_SHEET_ID, get_members_with_fees)
     record_step("fetch_members")
     if not members_data:
         return "No data."
     members, sorted_months = members_data
-        
+
     transactions = get_cached_data("payments_transactions", PAYMENTS_SHEET_ID, fetch_sheet_data, PAYMENTS_SHEET_ID, credentials_path)
     record_step("fetch_payments")
     exceptions = get_cached_data(
-            "exceptions_dict", PAYMENTS_SHEET_ID, fetch_exceptions,
-            PAYMENTS_SHEET_ID, credentials_path,
-            serialize=lambda d: [[list(k), v] for k, v in d.items()],
-            deserialize=lambda c: {tuple(k): v for k, v in c},
-        )
+        "exceptions_dict", PAYMENTS_SHEET_ID, fetch_exceptions,
+        PAYMENTS_SHEET_ID, credentials_path,
+        serialize=lambda d: [[list(k), v] for k, v in d.items()],
+        deserialize=lambda c: {tuple(k): v for k, v in c},
+    )
     record_step("fetch_exceptions")
     result = reconcile(members, sorted_months, transactions, exceptions)
     record_step("reconcile")
-    
-    month_labels = get_month_labels(sorted_months, ADULT_MERGED_MONTHS)
-    adult_names = sorted([name for name, tier, _ in members if tier == "A"])
-    current_month = datetime.now().strftime("%Y-%m")
 
-    monthly_totals = {m: {"expected": 0, "paid": 0} for m in sorted_months}
-    formatted_results = []
-    for name in adult_names:
-        data = result["members"][name]
-        row = {"name": name, "months": [], "balance": data["total_balance"], "unpaid_periods": "", "raw_unpaid_periods": ""}
-        unpaid_months = []
-        raw_unpaid_months = []
-        for m in sorted_months:
-            mdata = data["months"].get(m, {"expected": 0, "original_expected": 0, "attendance_count": 0, "paid": 0, "exception": None})
-            expected = mdata.get("expected", 0)
-            original_expected = mdata.get("original_expected", 0)
-            count = mdata.get("attendance_count", 0)
-            paid = int(mdata.get("paid", 0))
-            exception_info = mdata.get("exception", None)
-
-            monthly_totals[m]["expected"] += expected
-            monthly_totals[m]["paid"] += paid
-
-            override_amount = exception_info["amount"] if exception_info else None
-
-            if override_amount is not None and override_amount != original_expected:
-                is_overridden = True
-                fee_display = f"{override_amount} ({original_expected}) CZK ({count})" if count > 0 else f"{override_amount} ({original_expected}) CZK"
-            else:
-                is_overridden = False
-                fee_display = f"{expected} CZK ({count})" if count > 0 else f"{expected} CZK"
-
-            status = "empty"
-            cell_text = "-"
-            amount_to_pay = 0
-
-            if expected > 0:
-                amount_to_pay = max(0, expected - paid)
-                if paid >= expected:
-                    status = "ok"
-                    cell_text = f"{paid}/{fee_display}"
-                elif paid > 0:
-                    status = "partial"
-                    cell_text = f"{paid}/{fee_display}"
-                    if m < current_month:
-                        unpaid_months.append(month_labels[m])
-                        raw_unpaid_months.append(datetime.strptime(m, "%Y-%m").strftime("%m/%Y"))
-                else:
-                    status = "unpaid"
-                    cell_text = f"0/{fee_display}"
-                    if m < current_month:
-                        unpaid_months.append(month_labels[m])
-                        raw_unpaid_months.append(datetime.strptime(m, "%Y-%m").strftime("%m/%Y"))
-            elif paid > 0:
-                status = "surplus"
-                cell_text = f"PAID {paid}"
-            else:
-                cell_text = "-"
-                amount_to_pay = 0
-
-            if expected > 0 or paid > 0:
-                tooltip = f"Received: {paid}, Expected: {expected}"
-            else:
-                tooltip = ""
-
-            row["months"].append({
-                "text": cell_text,
-                "overridden": is_overridden,
-                "status": status,
-                "amount": amount_to_pay,
-                "month": month_labels[m],
-                "raw_month": m,
-                "tooltip": tooltip
-            })
-
-        # Balance = sum of (paid - expected) for past months only; current/future months ignored.
-        settled_balance = 0
-        for m, mdata in data["months"].items():
-            if m >= current_month:
-                continue
-            exp = mdata.get("expected", 0)
-            if isinstance(exp, int):
-                settled_balance += int(mdata.get("paid", 0)) - exp
-
-        payable_amount = max(0, -settled_balance)
-        row["unpaid_periods"] = ", ".join(unpaid_months)
-        row["raw_unpaid_periods"] = "+".join(raw_unpaid_months)
-        row["balance"] = settled_balance
-        row["payable_amount"] = payable_amount
-        formatted_results.append(row)
-
-    formatted_totals = []
-    for m in sorted_months:
-        t = monthly_totals[m]
-        status = "empty"
-        if t["expected"] > 0 or t["paid"] > 0:
-            if t["paid"] == t["expected"]:
-                status = "ok"
-            elif t["paid"] < t["expected"]:
-                status = "unpaid"
-            else:
-                status = "surplus"
-
-        formatted_totals.append({
-            "text": f"{t['paid']} / {t['expected']} CZK",
-            "status": status
-        })
-
-    def settled_balance(name):
-        data = result["members"][name]
-        total = 0
-        for m, mdata in data["months"].items():
-            if m >= current_month:
-                continue
-            exp = mdata.get("expected", 0)
-            if isinstance(exp, int):
-                total += int(mdata.get("paid", 0)) - exp
-        return total
-
-    credits = sorted([{"name": n, "amount": settled_balance(n)} for n in adult_names if settled_balance(n) > 0], key=lambda x: x["name"])
-    debts = sorted([{"name": n, "amount": abs(settled_balance(n))} for n in adult_names if settled_balance(n) < 0], key=lambda x: x["name"])
-    unmatched = result["unmatched"]
-    import json
-    
-    raw_payments_by_person = group_payments_by_person(transactions, [name for name, _, _ in members])
-    record_step("process_data")
-
-    return render_template(
-        "adults.html",
-        months=[month_labels[m] for m in sorted_months],
-        raw_months=sorted_months,
-        results=formatted_results,
-        totals=formatted_totals,
-        member_data=json.dumps(result["members"]),
-        month_labels_json=json.dumps(month_labels),
-        raw_payments_json=json.dumps(raw_payments_by_person),
-        credits=credits,
-        debts=debts,
-        unmatched=unmatched,
+    vm = build_adults_view_model(
+        members, sorted_months, result, transactions,
+        datetime.now().strftime("%Y-%m"),
         attendance_url=attendance_url,
         payments_url=payments_url,
         bank_account=BANK_ACCOUNT,
-        current_month=current_month
     )
+    record_step("process_data")
+    return render_template("adults.html", **vm)
 
 @app.route("/juniors")
 def juniors_view():
     attendance_url = f"https://docs.google.com/spreadsheets/d/{ATTENDANCE_SHEET_ID}/edit#gid={JUNIOR_SHEET_GID}"
     payments_url = f"https://docs.google.com/spreadsheets/d/{PAYMENTS_SHEET_ID}/edit"
-    
     credentials_path = CREDENTIALS_PATH
-    
+
     junior_members_data = get_cached_data("attendance_juniors", ATTENDANCE_SHEET_ID, get_junior_members_with_fees)
     record_step("fetch_junior_members")
     if not junior_members_data:
         return "No data."
     junior_members, sorted_months = junior_members_data
-        
+
     transactions = get_cached_data("payments_transactions", PAYMENTS_SHEET_ID, fetch_sheet_data, PAYMENTS_SHEET_ID, credentials_path)
     record_step("fetch_payments")
     exceptions = get_cached_data(
-            "exceptions_dict", PAYMENTS_SHEET_ID, fetch_exceptions,
-            PAYMENTS_SHEET_ID, credentials_path,
-            serialize=lambda d: [[list(k), v] for k, v in d.items()],
-            deserialize=lambda c: {tuple(k): v for k, v in c},
-        )
+        "exceptions_dict", PAYMENTS_SHEET_ID, fetch_exceptions,
+        PAYMENTS_SHEET_ID, credentials_path,
+        serialize=lambda d: [[list(k), v] for k, v in d.items()],
+        deserialize=lambda c: {tuple(k): v for k, v in c},
+    )
     record_step("fetch_exceptions")
 
-    # Adapt junior tuple format (name, tier, {month: (fee, total_count, adult_count, junior_count)}) 
-    # to what match_payments expects: (name, tier, {month: (expected_fee, attendance_count)})
-    adapted_members = []
-    for name, tier, fees_dict in junior_members:
-        adapted_fees = {}
-        for m, fee_data in fees_dict.items():
-            if len(fee_data) == 4:
-                fee, total_count, _, _ = fee_data
-                adapted_fees[m] = (fee, total_count)
-            else:
-                fee, count = fee_data
-                adapted_fees[m] = (fee, count)
-        adapted_members.append((name, tier, adapted_fees))
-
+    adapted_members = adapt_junior_members(junior_members)
     result = reconcile(adapted_members, sorted_months, transactions, exceptions)
     record_step("reconcile")
-    
-    # Format month labels
-    month_labels = get_month_labels(sorted_months, JUNIOR_MERGED_MONTHS)
-    junior_names = sorted([name for name, tier, _ in adapted_members])
-    junior_members_dict = {name: fees_dict for name, _, fees_dict in junior_members}
-    current_month = datetime.now().strftime("%Y-%m")
 
-    monthly_totals = {m: {"expected": 0, "paid": 0} for m in sorted_months}
-    formatted_results = []
-    for name in junior_names:
-        data = result["members"][name]
-        row = {"name": name, "months": [], "balance": data["total_balance"], "unpaid_periods": "", "raw_unpaid_periods": ""}
-        unpaid_months = []
-        raw_unpaid_months = []
-        for m in sorted_months:
-            mdata = data["months"].get(m, {"expected": 0, "original_expected": 0, "attendance_count": 0, "paid": 0, "exception": None})
-            expected = mdata.get("expected", 0)
-            original_expected = mdata.get("original_expected", 0)
-            count = mdata.get("attendance_count", 0)
-            paid = int(mdata.get("paid", 0))
-            exception_info = mdata.get("exception", None)
-
-            if expected != "?" and isinstance(expected, int):
-                monthly_totals[m]["expected"] += expected
-            monthly_totals[m]["paid"] += paid
-
-            orig_fee_data = junior_members_dict.get(name, {}).get(m)
-            adult_count = 0
-            junior_count = 0
-            if orig_fee_data and len(orig_fee_data) == 4:
-                _, _, adult_count, junior_count = orig_fee_data
-
-            breakdown = ""
-            if adult_count > 0 and junior_count > 0:
-                breakdown = f":{junior_count}J,{adult_count}A"
-            elif junior_count > 0:
-                breakdown = f":{junior_count}J"
-            elif adult_count > 0:
-                breakdown = f":{adult_count}A"
-
-            count_str = f" ({count}{breakdown})" if count > 0 else ""
-
-            override_amount = exception_info["amount"] if exception_info else None
-
-            if override_amount is not None and override_amount != original_expected:
-                is_overridden = True
-                fee_display = f"{override_amount} ({original_expected}) CZK{count_str}"
-            else:
-                is_overridden = False
-                fee_display = f"{expected} CZK{count_str}"
-
-            status = "empty"
-            cell_text = "-"
-            amount_to_pay = 0
-
-            if expected == "?" or (isinstance(expected, int) and expected > 0):
-                if expected == "?":
-                    status = "empty"
-                    cell_text = f"?{count_str}"
-                elif paid >= expected:
-                    status = "ok"
-                    cell_text = f"{paid}/{fee_display}"
-                elif paid > 0:
-                    status = "partial"
-                    cell_text = f"{paid}/{fee_display}"
-                    amount_to_pay = expected - paid
-                    if m < current_month:
-                        unpaid_months.append(month_labels[m])
-                        raw_unpaid_months.append(datetime.strptime(m, "%Y-%m").strftime("%m/%Y"))
-                else:
-                    status = "unpaid"
-                    cell_text = f"0/{fee_display}"
-                    amount_to_pay = expected
-                    if m < current_month:
-                        unpaid_months.append(month_labels[m])
-                        raw_unpaid_months.append(datetime.strptime(m, "%Y-%m").strftime("%m/%Y"))
-            elif paid > 0:
-                status = "surplus"
-                cell_text = f"PAID {paid}"
-
-            if (isinstance(expected, int) and expected > 0) or paid > 0:
-                tooltip = f"Received: {paid}, Expected: {expected}"
-            else:
-                tooltip = ""
-
-            row["months"].append({
-                "text": cell_text,
-                "overridden": is_overridden,
-                "status": status,
-                "amount": amount_to_pay,
-                "month": month_labels[m],
-                "raw_month": m,
-                "tooltip": tooltip
-            })
-
-        # Balance = sum of (paid - expected) for past months only; current/future months ignored.
-        settled_balance = 0
-        for m, mdata in data["months"].items():
-            if m >= current_month:
-                continue
-            exp = mdata.get("expected", 0)
-            if isinstance(exp, int):
-                settled_balance += int(mdata.get("paid", 0)) - exp
-
-        payable_amount = max(0, -settled_balance)
-        row["unpaid_periods"] = ", ".join(unpaid_months)
-        row["raw_unpaid_periods"] = "+".join(raw_unpaid_months)
-        row["balance"] = settled_balance
-        row["payable_amount"] = payable_amount
-        formatted_results.append(row)
-
-    formatted_totals = []
-    for m in sorted_months:
-        t = monthly_totals[m]
-        status = "empty"
-        if t["expected"] > 0 or t["paid"] > 0:
-            if t["paid"] == t["expected"]:
-                status = "ok"
-            elif t["paid"] < t["expected"]:
-                status = "unpaid"
-            else:
-                status = "surplus"
-
-        formatted_totals.append({
-            "text": f"{t['paid']} / {t['expected']} CZK",
-            "status": status
-        })
-
-    # Format credits and debts
-    def junior_settled_balance(name):
-        data = result["members"][name]
-        total = 0
-        for m, mdata in data["months"].items():
-            if m >= current_month:
-                continue
-            exp = mdata.get("expected", 0)
-            if isinstance(exp, int):
-                total += int(mdata.get("paid", 0)) - exp
-        return total
-
-    junior_all_names = [name for name, _, _ in adapted_members]
-    credits = sorted([{"name": n, "amount": junior_settled_balance(n)} for n in junior_all_names if junior_settled_balance(n) > 0], key=lambda x: x["name"])
-    debts = sorted([{"name": n, "amount": abs(junior_settled_balance(n))} for n in junior_all_names if junior_settled_balance(n) < 0], key=lambda x: x["name"])
-    unmatched = result["unmatched"]
-    raw_payments_by_person = group_payments_by_person(transactions, [name for name, _, _ in adapted_members])
-    import json
-
-    record_step("process_data")
-
-    return render_template(
-        "juniors.html",
-        months=[month_labels[m] for m in sorted_months],
-        raw_months=sorted_months,
-        results=formatted_results,
-        totals=formatted_totals,
-        member_data=json.dumps(result["members"]),
-        month_labels_json=json.dumps(month_labels),
-        raw_payments_json=json.dumps(raw_payments_by_person),
-        credits=credits,
-        debts=debts,
-        unmatched=unmatched,
+    vm = build_juniors_view_model(
+        junior_members, adapted_members, sorted_months, result, transactions,
+        datetime.now().strftime("%Y-%m"),
         attendance_url=attendance_url,
         payments_url=payments_url,
         bank_account=BANK_ACCOUNT,
-        current_month=current_month
     )
+    record_step("process_data")
+    return render_template("juniors.html", **vm)
 
 @app.route("/payments")
 def payments():
     attendance_url = f"https://docs.google.com/spreadsheets/d/{ATTENDANCE_SHEET_ID}/edit"
     payments_url = f"https://docs.google.com/spreadsheets/d/{PAYMENTS_SHEET_ID}/edit"
     credentials_path = CREDENTIALS_PATH
-    
+
     transactions = get_cached_data("payments_transactions", PAYMENTS_SHEET_ID, fetch_sheet_data, PAYMENTS_SHEET_ID, credentials_path)
     record_step("fetch_payments")
 
@@ -567,23 +310,13 @@ def payments():
     if juniors_data:
         member_names.extend(name for name, _, _ in juniors_data[0])
 
-    grouped = group_payments_by_person(transactions, member_names)
-    # payments page also groups unmatched rows under a fallback key
-    for tx in transactions:
-        if not str(tx.get("person", "")).strip():
-            grouped.setdefault("Unmatched / Unknown", []).append(tx)
-    for rows in grouped.values():
-        rows.sort(key=lambda t: str(t.get("date", "")), reverse=True)
-    sorted_people = sorted(grouped.keys())
-
-    record_step("process_data")
-    return render_template(
-        "payments.html",
-        grouped_payments=grouped,
-        sorted_people=sorted_people,
+    vm = build_payments_view_model(
+        transactions, member_names,
         attendance_url=attendance_url,
-        payments_url=payments_url
+        payments_url=payments_url,
     )
+    record_step("process_data")
+    return render_template("payments.html", **vm)
 
 @app.route("/qr")
 def qr_code():

docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md

@@ -2,9 +2,9 @@
 
 Companion to [2026-05-03-2349-go-backend-rewrite.md](2026-05-03-2349-go-backend-rewrite.md).
 
-**Current milestone:** M2 — Pure-domain helpers
+**Current milestone:** M6 — Go-native HTML frontend
 **Started:** 2026-05-04
-**Last updated:** 2026-05-06
+**Last updated:** 2026-05-08 (M6.6 + M6.6.1 merged)
 
 ## How to use
 
@@ -49,13 +49,13 @@ Each task: port the function, write Go unit tests for fresh cases, hook into the
 - [x] **M2.3** `domain/fees.CalculateFee` — port [attendance.py](scripts/attendance.py) `calculate_fee` (constants table) — `0fc3b6d`
 - [x] **M2.4** `domain/fees.CalculateJuniorFee` — port `calculate_junior_fee` with `Expected{Value int; Unknown bool}` for the `"?"` sentinel — `0fc3b6d`
 - [x] **M2.5** `domain/money.ParseCZK` — port [infer_payments.py](scripts/infer_payments.py) `parse_czk_amount` (Czech locale: comma decimal, dot/space thousand separators) — `d24d205`
-- [ ] **M2.6** `domain/synch.GenerateSyncID` — port [sync_fio_to_sheets.py](scripts/sync_fio_to_sheets.py) `generate_sync_id` (SHA-256, byte-stable hash; verify float string format against real sheet rows)
-- [ ] **M2.7** `domain/matching.BuildNameVariants` + `MatchMembers` — port `_build_name_variants` and `match_members` from [match_payments.py](scripts/match_payments.py) (auto vs review confidence, common-surname filter)
-- [ ] **M2.8** `domain/matching.InferTransactionDetails` — port `infer_transaction_details` (composes name + month parsing)
-- [ ] **M2.9** `domain/matching.FormatDate` — port `format_date` (handles Google Sheets serial-day numbers since 1899-12-30)
-- [ ] **M2.10** `domain/reconcile.Reconcile` — port `reconcile` (three-phase allocation: greedy / proportional with float-remainder absorption / even-split fallback). The single most load-bearing function; budget extra time.
-- [ ] **M2.11** `fuj fees` subcommand wired up via `domain/fees` + (M4-stub) attendance loader — fail gracefully on missing IO until M4 lands
-- [ ] **M2.12** `fuj reconcile` subcommand similarly stubbed
+- [x] **M2.6** `domain/synch.GenerateSyncID` — port [sync_fio_to_sheets.py](scripts/sync_fio_to_sheets.py) `generate_sync_id` (SHA-256, byte-stable hash; verify float string format against real sheet rows)
+- [x] **M2.7** `domain/matching.BuildNameVariants` + `MatchMembers` — port `_build_name_variants` and `match_members` from [match_payments.py](scripts/match_payments.py) (auto vs review confidence, common-surname filter) — `e596f00`
+- [x] **M2.8** `domain/matching.InferTransactionDetails` — port `infer_transaction_details` (composes name + month parsing) — `e596f00`
+- [x] **M2.9** `domain/matching.FormatDate` — port `format_date` (handles Google Sheets serial-day numbers since 1899-12-30) — `e596f00`
+- [x] **M2.10** `domain/reconcile.Reconcile` — port `reconcile` (three-phase allocation: greedy / proportional with float-remainder absorption / even-split fallback). The single most load-bearing function; budget extra time. — `c53bf5a`
+- [x] **M2.11** `fuj fees` subcommand wired up via `domain/fees` + (M4-stub) attendance loader — fail gracefully on missing IO until M4 lands — `56aa230`
+- [x] **M2.12** `fuj reconcile` subcommand similarly stubbed — `56aa230`
 
 **Gate:** `cd go && go test -tags=parity ./tests/parity/pure/...` green for every fixture in `tests/fixtures/pure/`.
 
@@ -65,14 +65,14 @@ Each task: port the function, write Go unit tests for fresh cases, hook into the
 
 Goal: deterministic, PII-free fixture corpus that drives parity tests. Runs in parallel with M2 (M3.1/M3.2 unblocks M2.1).
 
-- [ ] **M3.1** `scripts/capture_fixtures.py` — pure-function output dumper. Reads inputs from stdin / argv, prints `{"input":..., "output":...}` JSON
-- [ ] **M3.2** `scripts/scrub_fixtures.py` — replaces names with `Member_<8hex>` (deterministic per name); scrambles sender/account/VS/bank_id with stable bijection; preserves dates, amounts, exception keys
-- [ ] **M3.3** Capture pure-fn fixtures for M2.1–M2.9 (run helper + scrubber, commit to `tests/fixtures/pure/<func>/<case>.json`)
-- [ ] **M3.4** Capture ~10 reconcile fixtures spanning every code path: greedy, proportional (float remainder), even-split, out-of-window credit, exception override, `other:` purpose, junior `"?"`, multi-person comma-split, multi-month range, unmatched. Commit to `tests/fixtures/reconcile/`
-- [ ] **M3.5** Hook fixtures into Tier-1 test runner with `-tags=parity` build constraint
-- [ ] **M3.6** Document fixture-refresh workflow in `tests/fixtures/README.md` (what to do when sheet schema changes)
+- [x] **M3.1** `scripts/capture_fixtures.py` — pure-function output dumper. Reads inputs from stdin / argv, prints `{"input":..., "output":...}` JSON — `57518a8`
+- [x] **M3.2** `scripts/scrub_fixtures.py` — replaces names with `Member_<8hex>` (deterministic per name); scrambles sender/account/VS/bank_id with stable bijection; preserves dates, amounts, exception keys — `57518a8`
+- [x] **M3.3** Capture pure-fn fixtures for M2.1–M2.9 (run helper + scrubber, commit to `tests/fixtures/pure/<func>/<case>.json`) — `57518a8`
+- [x] **M3.4** Capture ~10 reconcile fixtures spanning every code path: greedy, proportional (float remainder), even-split, out-of-window credit, exception override, `other:` purpose, junior `"?"`, multi-person comma-split, multi-month range, unmatched. Commit to `tests/fixtures/reconcile/` — `57518a8`
+- [x] **M3.5** Hook fixtures into Tier-1 test runner with `-tags=parity` build constraint — `57518a8`
+- [x] **M3.6** Document fixture-refresh workflow in `tests/fixtures/README.md` (what to do when sheet schema changes) — `57518a8`
 
-**Gate:** `tests/fixtures/` populated; M2 parity tests green; raw `tmp/*.json` confirmed gitignored.
+**Gate:** ✅ `tests/fixtures/` populated (98 files); `make go-parity` green; `make go-lint` (parity tag) clean; raw `tmp/*.json` confirmed gitignored. Merged as `57518a8`.
 
 ---
 
@@ -80,16 +80,16 @@ Goal: deterministic, PII-free fixture corpus that drives parity tests. Runs in p
 
 Goal: every external IO (Sheets, Drive, Fio, file cache) accessed through a narrow Go interface with both a real and a fake implementation.
 
-- [ ] **M4.1** Design IO interfaces (`SheetsClient`, `DriveClient`, `FioClient`, `FileCache`) + in-memory fakes seeded from M3 fixtures
-- [ ] **M4.2** `internal/io/sheets` — Google client (read + append + batchUpdate); integration test against a separate test sheet (NOT prod)
-- [ ] **M4.3** `internal/io/drive` — Drive `modifiedTime` client + integration test
-- [ ] **M4.4** `internal/io/fio` — API JSON impl (token-based); parses by hardcoded `column0..column22` indices matching [fio_utils.py](scripts/fio_utils.py)
-- [ ] **M4.5** `internal/io/fio` — transparent-page HTML scraper using `golang.org/x/net/html` token visitor; targets the **second** `<table class="table">`
-- [ ] **M4.6** `internal/io/cache` — FileCache with `modifiedTime` gating + two TTL knobs + atomic writes (`os.Rename`)
-- [ ] **M4.7** `services/banksync.SyncToSheets` + `fuj sync` subcommand
-- [ ] **M4.8** `services/banksync.InferPayments` + `fuj infer [--dry-run]` subcommand
+- [x] **M4.1** Design IO interfaces (`SheetsClient`, `DriveClient`, `FioClient`, `FileCache`) + in-memory fakes seeded from M3 fixtures
+- [x] **M4.2** `internal/io/sheets` — Google client (read + append + batchUpdate); fake with call-capture
+- [x] **M4.3** `internal/io/drive` — Drive `modifiedTime` client + fake
+- [x] **M4.4** `internal/io/fio` — API JSON impl (token-based); parses by hardcoded `column0..column22` indices matching [fio_utils.py](scripts/fio_utils.py)
+- [x] **M4.5** `internal/io/fio` — transparent-page HTML scraper using `golang.org/x/net/html` token visitor; targets the **second** `<table class="table">`
+- [x] **M4.6** `internal/io/cache` — FileCache with `modifiedTime` gating + two TTL knobs + atomic writes (`os.Rename`)
+- [x] **M4.7** `services/banksync.SyncToSheets` + `fuj sync` subcommand
+- [x] **M4.8** `services/banksync.InferPayments` + `fuj infer [--dry-run]` subcommand; `NewSources` wires all IO into fees+reconcile
 
-**Gate:** `go test -tags=integration ./internal/io/...` round-trips against test sheet; default-tag tests run on fakes.
+**Gate:** ✅ Fakes-only unit tests; `make go-test` + `make go-lint` both green. Live smoke test deferred to first real sync run.
 
 ---
 
@@ -97,10 +97,10 @@ Goal: every external IO (Sheets, Drive, Fio, file cache) accessed through a narr
 
 Goal: byte-equal JSON between Python and Go for every route. This is the parity contract.
 
-- [ ] **M5.1** Hand-author Go structs for `/api/adults`, `/api/juniors`, `/api/payments`, `/api/version` with explicit `json:` tags matching Python keys; emit JSON Schemas via `github.com/invopop/jsonschema` to `tests/fixtures/api-schema/`
-- [ ] **M5.2** Implement Go handlers for `/api/*` routes composing `services/*` results into the JSON structs
-- [ ] **M5.3** Add Python `/api/X` shadow endpoints in [app.py](app.py): `jsonify(view_model_dict)` — no transformation
-- [ ] **M5.4** Build `cmd/parity/main.go`: hits both backends' `/api/X`, normalizes allowlist (`render_time.total`, `build_meta`), prints `cmp.Diff`. Add `make parity` target
+- [x] **M5.1** Hand-author Go structs for `/api/adults`, `/api/juniors`, `/api/payments`, `/api/version` with explicit `json:` tags matching Python keys; emit JSON Schemas via `github.com/invopop/jsonschema` to `tests/fixtures/api-schema/` — `f253e3f`
+- [x] **M5.2** Implement Go handlers for `/api/*` routes composing `services/*` results into the JSON structs — `7d48e8f`
+- [x] **M5.3** Add Python `/api/X` shadow endpoints in [app.py](app.py): `jsonify(view_model_dict)` — no transformation — `40e4a9e`
+- [x] **M5.4** Build `cmd/parity/main.go`: hits both backends' `/api/X`, normalizes allowlist (`render_time.total`, `build_meta`), prints `cmp.Diff`. Add `make parity` target
 
 **Gate:** For each route, `make parity` reports zero non-allowlisted diffs across the M3 fixture corpus.
 
@@ -110,13 +110,14 @@ Goal: byte-equal JSON between Python and Go for every route. This is the parity
 
 Goal: feature-equivalent UX on the Go side, designed cleanly. Not a Jinja port.
 
-- [ ] **M6.1** Template skeleton: base layout, nav (Adults/Juniors/Payments/Sync/Flush), terminal-green-on-black theme; `embed.FS` for `templates/` + `static/`
-- [ ] **M6.2** `/adults` page: table, name filter input, month range filter, totals row, credits/debts/unmatched sections, Pay buttons that link to `/qr`
-- [ ] **M6.3** `/juniors` page: same structure + per-month J/A attendance breakdown + `"?"` sentinel rendering
-- [ ] **M6.4** `/payments` page: grouped-by-person ledger view
-- [ ] **M6.5** Modal JS module (`static/js/member-detail.js`): fetches `/api/adults` (or juniors), renders status/exceptions/transactions on row click; keyboard nav (Esc, ↑/↓)
-- [ ] **M6.6** `/qr`, `/sync-bank`, `/flush-cache`, `/version` pages
-- [ ] **M6.7** Wire `embed.FS` into handlers; verify single-binary deployment includes all assets
+- [x] **M6.1** Template skeleton: base layout, nav (Adults/Juniors/Payments/Sync/Flush), terminal-green-on-black theme; `embed.FS` for `templates/` + `static/` — `78e5059`
+- [x] **M6.2** `/adults` page: table, name filter input, month range filter, totals row, credits/debts/unmatched sections, Pay buttons that link to `/qr` — `c85748b`
+- [x] **M6.3** `/juniors` page: same structure + per-month J/A attendance breakdown + `"?"` sentinel rendering — `9564103`
+- [x] **M6.4** `/payments` page: grouped-by-person ledger view — `689f1c0`
+- [x] **M6.5** Modal JS module (`static/js/member-detail.js`): fetches `/api/adults` (or juniors), renders status/exceptions/transactions on row click; keyboard nav (Esc, ↑/↓) — `e53e238`
+- [x] **M6.6** `/qr`, `/sync-bank`, `/flush-cache`, `/version` pages — `f6ba85b`
+- [x] **M6.6.1** Pay-button QR popup modal (`payment-qr.js`); restores Python `showPayQR` UX lost in M6.6 — `4276d7b`
+- [ ] **M6.7** Wire `embed.FS` into handlers; verify single-binary deployment includes all assets — (pending merge)
 
 **Gate:** Browser smoke on :8080: all pages render, name+month filters work, modal opens with correct data, QR loads, sync/flush work end-to-end.
 
@@ -154,5 +155,7 @@ Goal: Go is the one true backend.
 
 (Add entries as you go. Format: `YYYY-MM-DD — short note`.)
 
+- 2026-05-07 — `/api/version` excluded from parity diff by design. Each binary's tag/commit/build_date is identity, not a data contract — diffing it would always flag a diff between independently built backends. Route remains reachable via `make parity ARGS="-route /api/version"` for manual inspection.
 - 2026-05-04 — Plan approved. Versioning policy: latest stable for Go and all libs at the time M1 starts. Frontends explicitly allowed to diverge between Python and Go; only the JSON API contract is parity-locked. No reverse proxy — both backends run on different ports via `make web-py` / `make web-go`.
+- 2026-05-07 — M4 complete. Chose fakes-only unit tests (no live integration tests) and CSV-via-public-URL for attendance (no Sheets API auth required for read-only). golangci-lint gofumpt extra-rules differ slightly from standalone gofumpt; used `golangci-lint run --fix --enable-only gofumpt` to auto-resolve formatting.
 - 2026-05-04 — M1 complete. Dockerfile base changed from `distroless/static:nonroot` → `alpine:3` for debuggability (can tighten later). CLI dispatcher uses stdlib `flag`; module path `fuj-management/go`. golangci-lint v1 embedded gofumpt merges all imports into one group (no stdlib/local split) — accepted as the project style.

docs/plans/2026-05-06-1236-go-m2-6-synch-generate-sync-id.md

@@ -0,0 +1,265 @@
+
+## Context
+
+Continuing the Go backend rewrite tracked in
+[2026-05-03-2349-go-backend-rewrite-progress.md](../../srv/personal/fuj-management/docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md).
+M2.1–M2.5 are landed. Next leaf-level pure function is `generate_sync_id`
+from [scripts/sync_fio_to_sheets.py:62-77](../../srv/personal/fuj-management/scripts/sync_fio_to_sheets.py#L62-L77).
+
+It computes a SHA-256 hash over a fixed seven-field projection of a Fio
+transaction (`date|amount|currency|sender|vs|message|bank_id`) and is
+the deduplication key written into column K (`Sync ID`) of the payments
+sheet. The Go port must produce a **byte-identical** digest for the same
+transaction; otherwise the Go-side sync (M4.7) would re-append rows
+already written by the Python sync, double-counting payments.
+
+The non-trivial part is the `amount` field's string serialisation:
+upstream `fio_utils.py` always supplies `amount` as a Python `float`
+(API path: `float(val(1) or 0)`; HTML path: `parse_czech_amount(...)`
+which returns `float`). Python's `str(float)` produces `"500.0"` for
+whole-valued floats; Go's `strconv.FormatFloat(f, 'g', -1, 64)` produces
+`"500"`. This is the gotcha called out in the M2.6 line of the progress
+tracker.
+
+## Python behaviour (the spec)
+
+```py
+def generate_sync_id(tx: dict) -> str:
+    components = [
+        str(tx.get("date", "")),
+        str(tx.get("amount", "")),
+        str(tx.get("currency", "CZK")),
+        str(tx.get("sender", "")),
+        str(tx.get("vs", "")),
+        str(tx.get("message", "")),
+        str(tx.get("bank_id", "")),
+    ]
+    raw_str = "|".join(components).lower()
+    return hashlib.sha256(raw_str.encode("utf-8")).hexdigest()
+```
+
+Behavioural notes for the Go port:
+
+1. **Field order is load-bearing.** `date|amount|currency|sender|vs|message|bank_id` exactly.
+2. **Separator is `"|"`.**
+3. **Whole string is `.lower()`-ed before hashing** (so e.g. "ABC" sender vs "abc" hash identically). Unicode lower; in practice Fio data is ASCII + Czech diacritics.
+4. **`currency` defaults to `"CZK"`** when missing from the dict (HTML scraper path never sets it). Other fields default to `""`.
+5. **`amount` is a `float`.** Always. Real Fio data is `500.0`, `1234.56`, etc. — no NaN/Inf, but parity test must pin the format.
+6. **Output is `hashlib.sha256(...).hexdigest()`** — 64-char lowercase hex.
+7. **Encoding is UTF-8.**
+
+### `str(float)` cases observed in real Fio amounts
+
+| float64 | Python `str(f)` | Go `strconv.FormatFloat(f,'g',-1,64)` | Need |
+|---|---|---|---|
+| `500.0` | `"500.0"` | `"500"` | append `.0` |
+| `1234.56` | `"1234.56"` | `"1234.56"` | matches |
+| `0.0` | `"0.0"` | `"0"` | append `.0` |
+| `-500.0` | `"-500.0"` | `"-500"` | append `.0` |
+| `0.1` | `"0.1"` | `"0.1"` | matches |
+| `99999.99` | `"99999.99"` | `"99999.99"` | matches |
+
+For the Fio amount domain (signed CZK, ≤ ~7 digits, ≤2 decimal places),
+the rule "`'g'` with prec -1, then append `.0` if result has no `.` and
+no `e`/`E`" is exact. We do not need to handle Python's
+scientific-notation crossover (`>= 1e16`) for real data, but the
+implementation should still cope with it correctly via the same rule.
+
+## Approach
+
+Create new package `internal/domain/synch` mirroring the layout of
+`internal/domain/money` (single-file module + test file alongside).
+
+### Package + signature
+
+```go
+// Package synch ports the bank-sync deduplication helper from
+// scripts/sync_fio_to_sheets.py.
+package synch
+
+// Transaction is the projection of a Fio transaction that participates
+// in the Sync ID hash. Other fields (ks, ss, sender_account, …) are
+// intentionally excluded — they are not part of the Python hash.
+//
+// Currency: leave "" to inherit the Python default of "CZK" (matches
+// the HTML scraper path which omits the key entirely).
+type Transaction struct {
+    Date     string
+    Amount   float64
+    Currency string
+    Sender   string
+    VS       string
+    Message  string
+    BankID   string
+}
+
+// GenerateSyncID returns the lowercase SHA-256 hex digest of
+// "date|amount|currency|sender|vs|message|bank_id" (lower-cased), used
+// as the dedup key in column K of the payments sheet.
+//
+// Byte-stable with scripts/sync_fio_to_sheets.py generate_sync_id.
+func GenerateSyncID(tx Transaction) string
+```
+
+### `Currency` default
+
+In Go every struct field is always present, so we lose Python's
+"missing key vs empty string" distinction. Real-world data either sets
+`currency = "CZK"` (API path) or omits the key (HTML path → `"CZK"`
+default). Empty string never occurs in practice. The Go port collapses
+the two by treating `Currency == ""` as "use `CZK`":
+
+```go
+currency := tx.Currency
+if currency == "" {
+    currency = "CZK"
+}
+```
+
+This is byte-equal to Python for every input we will ever see in
+production, and avoids forcing callers to pass a `*string`.
+
+### Float formatter
+
+Internal helper, unexported:
+
+```go
+// formatAmount mimics Python's str(float) for the float values that
+// appear in Fio transactions. For mundane decimal amounts the rule
+// is: format with 'g' precision -1, then append ".0" if the result
+// has no decimal point and no exponent.
+func formatAmount(f float64) string {
+    s := strconv.FormatFloat(f, 'g', -1, 64)
+    if !strings.ContainsAny(s, ".eE") {
+        s += ".0"
+    }
+    return s
+}
+```
+
+Tested explicitly (see Tests below) so the edge cases (`0`, whole
+numbers, negatives, large/small with exponent) stay locked.
+
+### Hash composition
+
+```go
+func GenerateSyncID(tx Transaction) string {
+    currency := tx.Currency
+    if currency == "" {
+        currency = "CZK"
+    }
+    raw := strings.ToLower(strings.Join([]string{
+        tx.Date,
+        formatAmount(tx.Amount),
+        currency,
+        tx.Sender,
+        tx.VS,
+        tx.Message,
+        tx.BankID,
+    }, "|"))
+    sum := sha256.Sum256([]byte(raw))
+    return hex.EncodeToString(sum[:])
+}
+```
+
+(`crypto/sha256` + `encoding/hex` — both stdlib, no `go.mod` change.)
+
+## Tests
+
+`synch_test.go` mirrors `money_test.go`'s table-driven style with the
+verification snippet at the top of the function. Two test functions:
+
+### 1. `TestGenerateSyncID`
+
+Each row's expected digest is computed from the Python source:
+
+```sh
+PYTHONPATH=scripts:. python -c '
+from sync_fio_to_sheets import generate_sync_id
+cases = [
+    {"date":"2026-01-15","amount":500.0,"currency":"CZK","sender":"Jan Novak","vs":"123","message":"clenske 1/2026","bank_id":"abc123"},
+    {"date":"2026-01-15","amount":500.0,"sender":"Jan Novak","vs":"123","message":"clenske 1/2026","bank_id":"abc123"},  # currency missing → CZK
+    {"date":"2026-02-10","amount":1234.56,"currency":"CZK","sender":"ABC SRO","vs":"","message":"FAKTURA 42","bank_id":"xyz"},  # mixed case → lowercased
+    {"date":"2026-03-01","amount":-500.0,"currency":"CZK","sender":"refund","vs":"","message":"","bank_id":""},  # negative
+    {"date":"2026-04-01","amount":0.0,"currency":"CZK","sender":"","vs":"","message":"","bank_id":""},  # zero amount
+    {},  # empty dict — every field falls back to default
+]
+for c in cases:
+    print(repr(c), "->", generate_sync_id(c))
+'
+```
+
+Cases (one row per dict above), each asserting the exact 64-char hex
+digest the snippet prints. Cover:
+
+- Happy path with all fields set.
+- `Currency: ""` → `"CZK"` default (parity with missing key).
+- Mixed-case sender/message → lowercased before hashing.
+- Negative amount.
+- Zero amount.
+- Zero-value `Transaction{}` — every field at Go zero, currency defaults
+  to `"CZK"`, hash matches Python `generate_sync_id({})`.
+
+### 2. `TestFormatAmount`
+
+Pin the float formatter against Python's `str(float)`:
+
+```sh
+PYTHONPATH=scripts:. python -c '
+for v in [0.0, 500.0, -500.0, 0.1, 1234.56, 99999.99, 1500000.0, 1e16, 1e-5]:
+    print(repr(v), "->", repr(str(v)))
+'
+```
+
+Table of `(float64, expected string)` pairs. Whole numbers must end in
+`.0`; existing decimal representations pass through unchanged;
+exponent-form floats (`1e16`, `1e-5`) keep their format.
+
+## Files to create
+
+- `go/internal/domain/synch/synch.go` — package, `Transaction`,
+  `GenerateSyncID`, internal `formatAmount`.
+- `go/internal/domain/synch/synch_test.go` — `TestGenerateSyncID` +
+  `TestFormatAmount`.
+
+No existing Go files need editing.
+
+## Verification
+
+```sh
+cd go && go test ./internal/domain/synch/...
+make go-lint
+make go-build   # sanity: nothing else broke
+```
+
+Plus run the two Python snippets in the Tests section and diff their
+output against the test tables to confirm parity.
+
+## Out of scope (explicit non-goals)
+
+- **Hooking into the Tier-1 parity runner.** That comes with M3.5
+  (`-tags=parity` build constraint and `tests/fixtures/pure/`). M2.6
+  ships with hand-written, Python-verified test tables — same approach
+  used by M2.1–M2.5.
+- **A richer `Transaction` struct** covering ks/ss/note/sender_account.
+  Those fields aren't part of the hash. M4.4 (Fio IO adapter) will
+  decide whether to reuse `synch.Transaction` or define its own struct
+  and convert at the boundary.
+- **Polymorphic input** (e.g. accepting a `map[string]any`). Python's
+  duck-typing is a non-goal in Go.
+- **Any Python callsite migration.** `sync_fio_to_sheets.py` keeps using
+  its own `generate_sync_id` until M4.7 ports the sync service.
+
+## Progress tracker + changelog
+
+After the commit lands:
+
+- Tick `M2.6` in
+  [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](../../srv/personal/fuj-management/docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md)
+  with the commit SHA, mirroring the M2.5 entry style.
+- Add a `CHANGELOG.md` entry at top:
+  `## YYYY-MM-DD HH:MM TZ — feat(go/M2.6): port domain/synch.GenerateSyncID`.
+
+Branch: `feat/m2-6-synch-generate-sync-id` (per CLAUDE.md
+branch-per-feature workflow). Push, open MR via `tea pr create`, leave
+merge to the user.

docs/plans/2026-05-06-1305-go-m2-7-2-9-matching.md

@@ -0,0 +1,126 @@
+# M2.7 + M2.8 + M2.9 — Port `matching` package to Go
+
+> On approval: copy this plan to `docs/plans/2026-05-06-1305-go-m2-7-2-9-matching.md` per [CLAUDE.md](../../srv/personal/fuj-management/CLAUDE.md) plan-location convention.
+
+## Context
+
+The Go rewrite (tracked in [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](../../srv/personal/fuj-management/docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md)) is in milestone M2 — porting pure-domain helpers leaf-first from Python to Go. M2.1 through M2.6 are complete (`czech.Normalize`, `czech.ParseMonthReferences`, `fees.CalculateFee`, `fees.CalculateJuniorFee`, `money.ParseCZK`, `synch.GenerateSyncID`).
+
+M2.7, M2.8, and M2.9 cover three helpers from [scripts/match_payments.py](../../srv/personal/fuj-management/scripts/match_payments.py) that form a tight chain: `InferTransactionDetails` calls `MatchMembers` which calls `BuildNameVariants` and the same Sheets-serial date logic that `FormatDate` uses. The user requested they be done together because the dependency graph makes per-milestone commits awkward — `MatchMembers` would either reference an unexported helper not yet committed or commit dead code.
+
+This unblocks M2.10 (`reconcile`, the load-bearing function) and M5 parity tests, since reconciliation consumes `InferTransactionDetails` output.
+
+## Approach
+
+**One commit, one branch, one MR.** Branch: `feat/m2-7-2-9-matching-package`. The three milestone checkboxes get ticked together on merge.
+
+### Package layout
+
+New package `go/internal/domain/matching/` mirroring the existing `go/internal/domain/{czech,fees,money,synch}` convention (one file per public symbol, tests alongside as `*_test.go`):
+
+| File | Contents |
+|---|---|
+| `doc.go` | `// Package matching ports name/member matching from scripts/match_payments.py.` |
+| `name_variants.go` | `BuildNameVariants` + unexported `wordIn` helper (mirrors Python's `_word_in` co-location at [match_payments.py:60-62](../../srv/personal/fuj-management/scripts/match_payments.py#L60)) |
+| `match_members.go` | `Confidence` typed string + constants, `Match` struct, `MatchMembers` |
+| `infer.go` | `Transaction`, `InferredDetails`, `InferTransactionDetails` |
+| `format_date.go` | `FormatDate` |
+| `name_variants_test.go`, `match_members_test.go`, `infer_test.go`, `format_date_test.go` | table-driven tests, each with a top-of-file comment quoting the live Python one-liner used to verify expected values (mirrors [synch_test.go:7-20](../../srv/personal/fuj-management/go/internal/domain/synch/synch_test.go#L7)) |
+
+### Public API
+
+```go
+type Confidence string
+const (
+    ConfidenceAuto   Confidence = "auto"
+    ConfidenceReview Confidence = "review"
+)
+type Match struct {
+    Name       string
+    Confidence Confidence
+}
+
+func BuildNameVariants(name string) []string
+func MatchMembers(text string, memberNames []string) []Match
+
+type Transaction struct {
+    Sender  string
+    Message string
+    UserID  string
+    Date    any // string | int | float64 — see "Parity concerns"
+}
+type InferredDetails struct {
+    Members    []Match
+    Months     []string
+    SearchText string // matches Python's "search_text" key, not the misleading "matched_text" docstring
+}
+func InferTransactionDetails(tx Transaction, memberNames []string, defaultYear int) InferredDetails
+
+func FormatDate(val any) string
+```
+
+### Algorithms (port verbatim — these are the load-bearing details)
+
+**`BuildNameVariants`** ([match_payments.py:33-57](../../srv/personal/fuj-management/scripts/match_payments.py#L33)): extract `(nickname)` regex, strip parens for `base`, normalize via `czech.Normalize`, append last + first when ≥2 parts, **filter <3 chars**. `variants[0]` must always be the full normalized base — `MatchMembers` relies on this.
+
+**`MatchMembers`** ([match_payments.py:65-137](../../srv/personal/fuj-management/scripts/match_payments.py#L65)):
+1. **Exact short-circuit** ([:77-84](../../srv/personal/fuj-management/scripts/match_payments.py#L77)): if any member's `variants[0]` whole-word matches in `Normalize(text)`, return ONLY those `(name, auto)`. Prevents nickname `tov` matching inside `ottova`.
+2. Otherwise per-member first-match-wins: full-name substring → `\b first \b` AND `\b last \b` (any order) → `\b nickname \b` — each yields `auto` and continues.
+3. **Review tier** ([:113-129](../../srv/personal/fuj-management/scripts/match_payments.py#L113)): ≥2-part names → last name `len ≥ 4` AND not in `{"novak","novakova","prach"}` → review; else first name `len ≥ 3` → review. 1-part names → `len ≥ 4` → review.
+4. **Final filter** ([:131-137](../../srv/personal/fuj-management/scripts/match_payments.py#L131)): if ANY auto exists, drop ALL review. Two-pass — don't try to fuse with the loop.
+
+**`InferTransactionDetails`** ([match_payments.py:144-184](../../srv/personal/fuj-management/scripts/match_payments.py#L144)): `search_text = sender + " " + message + " " + user_id`; month parse uses `message + " " + user_id` (excludes sender); fallback 1 retries members on sender alone; fallback 2 derives months from `tx.Date` (Sheets serial or `YYYY-MM-DD`).
+
+**`FormatDate`** ([match_payments.py:187-206](../../srv/personal/fuj-management/scripts/match_payments.py#L187)): nil/empty → `""`; int/float → Sheets serial since 1899-12-30 formatted `YYYY-MM-DD`; pre-formatted `YYYY-MM-DD` (length 10, dashes at idx 4/7) → as-is; else `strings.TrimSpace(fmt.Sprint(v))`. **No raise on bad input** — parity contract.
+
+## Parity concerns
+
+- **RE2 `\b`**: Equivalent to Python `\b` on ASCII-folded input (`Normalize` strips diacritics + lowercases). Use `regexp.QuoteMeta` for `re.escape`.
+- **Sheets epoch**: 1899-12-30 (NOT 1900-01-01). `time.Date(1899, 12, 30, 0, 0, 0, 0, time.UTC)`.
+- **Fractional serials**: Python `timedelta(days=44197.5)` adds 12 hours, then `.strftime("%Y-%m-%d")` discards time. To match exactly use `base.Add(time.Duration(val * 24 * float64(time.Hour)))` then `Format("2006-01-02")`. **Do NOT** use `base.AddDate(0, 0, int(val))` — that silently drops fractional days from real Sheets exports of timestamped cells.
+- **`Transaction.Date any`**: Python `tx["date"]` accepts int/float/string transparently. Sheets API returns serial dates as `float64` from JSON; FIO scraper returns `string`. `any` is the faithful port; type-switch inside `FormatDate` and the date fallback in `InferTransactionDetails`.
+- **`SearchText` vs `MatchedText`**: Python docstring says `matched_text`, code returns `"search_text"`. Port the code, not the docstring.
+- **Default year plumbing**: Go's `czech.ParseMonthReferences(text, defaultYear)` requires explicit year. Python defaults to 2026. Plumb `defaultYear` as the third arg to `InferTransactionDetails`.
+- **Empty slices not nil**: Python `match_members` returns `[]` when nothing matches; ensure Go returns `[]Match{}` not `nil` so consumers don't have to nil-check (matches `synch` package style).
+
+## Tests
+
+Port all 6 cases from [tests/test_match_members.py](../../srv/personal/fuj-management/tests/test_match_members.py) verbatim into `match_members_test.go` as one table-driven `TestMatchMembers`. Each row: `name`, `text`, `wantContains []string`, `wantExcludes []string`, `wantAllAuto bool`.
+
+Add table cases for:
+- `BuildNameVariants` — docstring example `František Vrbík (Štrúdl)` → 4 variants; nickname filtered (len<3); single-part name; whitespace inside parens
+- `FormatDate` — `nil` → `""`, `""` → `""`, `int(44197)` → `"2020-12-31"`, `float64(44197.5)` → `"2020-12-31"`, `"2026-04-15"` → `"2026-04-15"`, `"garbage"` → `"garbage"`, `"  2026-04-15  "` → `"2026-04-15"`
+- `InferTransactionDetails` — members from search_text, members from sender fallback, months from date-string fallback, months from serial-date fallback, both-paths-fail returns empty slices
+
+Verify expectations against live Python and quote the one-liner in a top-of-file comment, e.g.:
+
+```
+PYTHONPATH=scripts:. python -c '
+from match_payments import format_date
+for v in [None, "", 44197, 44197.5, "2026-04-15", "garbage", "  2026-04-15  "]: print(repr(format_date(v)))
+'
+```
+
+## Critical files
+
+- **Read for parity** — [scripts/match_payments.py:33-206](../../srv/personal/fuj-management/scripts/match_payments.py#L33), [tests/test_match_members.py](../../srv/personal/fuj-management/tests/test_match_members.py)
+- **Reuse** — `czech.Normalize` ([go/internal/domain/czech/normalize.go](../../srv/personal/fuj-management/go/internal/domain/czech/normalize.go#L15)), `czech.ParseMonthReferences` ([parse_month_references.go:61](../../srv/personal/fuj-management/go/internal/domain/czech/parse_month_references.go#L61))
+- **Mirror conventions** — [go/internal/domain/synch/synch.go](../../srv/personal/fuj-management/go/internal/domain/synch/synch.go), [go/internal/domain/synch/synch_test.go](../../srv/personal/fuj-management/go/internal/domain/synch/synch_test.go)
+- **New** — `go/internal/domain/matching/{doc,name_variants,match_members,infer,format_date}.go` + `*_test.go`
+
+## Out of scope (M2.10 / M4 territory — DO NOT touch)
+
+- `canonical_member_key` ([match_payments.py:20](../../srv/personal/fuj-management/scripts/match_payments.py#L20))
+- `reconcile`, `fetch_sheet_data`, `fetch_exceptions` — M2.10 / M4
+- Sheets/Drive/FIO I/O glue
+- Fixture capture (`tests/fixtures/pure/`) — M3.3 separately
+
+## Verification
+
+1. `cd go && make go-build` — clean build.
+2. `cd go && make go-test ./internal/domain/matching/...` — all table tests green.
+3. `cd go && make go-lint` — clean (govet, staticcheck, errcheck, gofumpt, unused).
+4. Spot-check: pick 2–3 random non-trivial cases (e.g. `MatchMembers` with mixed auto/review, `FormatDate(44197.5)`) and run the live Python one-liner from each test's comment block to confirm bytes match.
+5. Append CHANGELOG entry per [CLAUDE.md](../../srv/personal/fuj-management/CLAUDE.md) (timestamp via `date "+%Y-%m-%d %H:%M %Z"`).
+6. Tick M2.7, M2.8, M2.9 in [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](../../srv/personal/fuj-management/docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md) with the merge SHA.
+7. Push branch, open MR via `tea pr create --title "feat(go): port matching helpers (M2.7-2.9)" --base main --head feat/m2-7-2-9-matching-package`, print URL, leave merge to user.

docs/plans/2026-05-06-1626-infer-payments-junior-roster.md

@@ -0,0 +1,129 @@
+# Include junior members in payment inference roster
+
+## Context
+
+A bank payment from sender `JIŘÍ KUBÍK` with the message
+`Jáchym Kubík: 01/2026+03/2026+04/2026` is being inferred as
+`[?] Jáchym Hrušák (G)` instead of the obvious `Jáchym Kubík`, even though
+the message contains his exact full name.
+
+**Root cause** (confirmed with the user): `Jáchym Kubík` is in the **junior**
+attendance sheet only — he does not appear on the main/adults sheet. But
+[scripts/infer_payments.py:101-102](scripts/infer_payments.py#L101-L102)
+builds `member_names` by calling `get_members_with_fees()`
+([scripts/attendance.py:170](scripts/attendance.py#L170)), which reads only
+`EXPORT_URL` (the adults sheet). Junior-only members are therefore invisible
+to the matcher.
+
+With Kubík absent from `member_names`, the matcher in
+[scripts/match_payments.py:65](scripts/match_payments.py#L65) processes the
+combined text `jiri kubik jachym kubik: 01/2026+03/2026+04/2026` against an
+adults-only roster:
+
+- The exact-full-name short-circuit (`match_payments.py:75-84`) finds nothing —
+  no adult's full name is in the text.
+- Hrušák `(G)` is the only adult with first name `Jáchym`. He fails the
+  auto-rules (his surname isn't in the text) but hits the partial-first-name
+  review rule (`match_payments.py:123-125`) → returned as `("Jáchym Hrušák (G)",
+  "review")`, rendered as `[?] Jáchym Hrušák (G)`.
+
+The user's original framing — "exact match in message should win over
+everything" — is already implemented for any candidate that **is** in the
+roster (the May-04 short-circuit). The bug is upstream: the right candidate
+was never even considered.
+
+**Goal:** make `infer_payments` consider junior members as candidates, so
+junior-only names like `Jáchym Kubík` get matched correctly.
+
+## Approach
+
+Single-file change in [scripts/infer_payments.py](scripts/infer_payments.py).
+
+Replace the adults-only roster lookup with a union of the adult and junior
+rosters. `attendance.py` already exposes both:
+[`get_members_with_fees()`](scripts/attendance.py#L170) for adults (and tier-J
+juniors who train with adults) and
+[`get_junior_members_with_fees()`](scripts/attendance.py#L208) for everyone in
+the junior sheet.
+
+### Edit at [scripts/infer_payments.py:15](scripts/infer_payments.py#L15)
+
+```python
+from attendance import get_members_with_fees, get_junior_members_with_fees
+```
+
+### Edit at [scripts/infer_payments.py:99-102](scripts/infer_payments.py#L99-L102)
+
+```python
+print("Fetching member list for matching...")
+adult_members, _ = get_members_with_fees()
+junior_members, _ = get_junior_members_with_fees()
+
+# Union rosters, preserving first-seen order, deduping by canonical key
+seen: set[str] = set()
+member_names: list[str] = []
+for m in adult_members + junior_members:
+    name = m[0]
+    key = canonical_member_key(name)
+    if key in seen:
+        continue
+    seen.add(key)
+    member_names.append(name)
+```
+
+`canonical_member_key` already lives in
+[scripts/match_payments.py:20](scripts/match_payments.py#L20) — import it
+alongside `infer_transaction_details`. It normalizes diacritics/case/whitespace,
+so `"Maria Maco"` and `"Mária Maco"` collapse to the same key.
+
+### Why downstream reconciliation still works
+
+`reconcile()` is invoked twice per page — once with the adults roster
+([app.py:200](app.py#L200)) and once with the juniors roster
+([app.py:384](app.py#L384)). Each call resolves the `Person` cell against its
+own roster; a junior name resolves cleanly in the juniors call and lands in
+"unmatched" in the adults call. That's already the existing behavior for any
+junior payment manually entered into the `Person` column, so no further
+changes are needed.
+
+### Files to modify
+
+- [scripts/infer_payments.py](scripts/infer_payments.py) — only the
+  import + roster construction. ~10-line change.
+
+### Files to read for confidence (no edits)
+
+- [scripts/attendance.py:208-289](scripts/attendance.py#L208-L289) —
+  `get_junior_members_with_fees` returns `(name, tier, …)` tuples just like
+  the adults version, so `m[0]` works for both.
+- [scripts/match_payments.py:65-137](scripts/match_payments.py#L65-L137) —
+  `match_members` already handles the precedence the user wants (exact full-name
+  short-circuit), so once Kubík is in `member_names`, the case will be auto-matched
+  with no `[?]`.
+
+## Verification
+
+1. **Manual sanity** — re-run inference on the offending row:
+   - Clear `Person`/`Purpose` for the Kubík row in the payments sheet.
+   - `make infer`.
+   - Expect `Person = Jáchym Kubík`, `Purpose = 2026-01, 2026-03, 2026-04`,
+     no `[?]`.
+
+2. **Unit test** — extend
+   [tests/test_match_members.py](tests/test_match_members.py) (or add a small
+   `tests/test_infer_payments.py`) to assert that, given a roster that
+   includes `Jáchym Hrušák (G)` and `Jáchym Kubík`, the message
+   `Jáchym Kubík: 01/2026+03/2026+04/2026` resolves to
+   `[("Jáchym Kubík", "auto")]` only. This is really a regression test for
+   the May-04 short-circuit — the new behavior under test is just that
+   `infer_payments` now feeds in juniors.
+
+3. **Run the suite**: `make test`.
+
+4. **Dashboard smoke** — `make web`, open `/payments`, confirm the row now
+   shows the correct member; open `/juniors`, confirm the payment is
+   credited to Kubík for the three months listed.
+
+5. **Changelog** — once the user confirms the fix, append an entry to
+   [CHANGELOG.md](CHANGELOG.md) per [CLAUDE.md](CLAUDE.md):
+   `## YYYY-MM-DD HH:MM TZ — fix: include juniors in payment-inference roster`.

docs/plans/2026-05-06-1738-go-m2-11-12-fees-reconcile-cli.md

@@ -0,0 +1,215 @@
+# M2.11 + M2.12 — `fuj fees` and `fuj reconcile` subcommands (stubbed IO)
+
+> On approval: copy this plan to `docs/plans/2026-05-06-1738-go-m2-11-12-fees-reconcile-cli.md` per [CLAUDE.md](../../CLAUDE.md) plan-location convention.
+
+## Context
+
+The Go rewrite (tracked in [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](2026-05-03-2349-go-backend-rewrite-progress.md)) finished M2.1–M2.10 — every pure-domain helper (`czech`, `fees`, `money`, `synch`, `matching`, `reconcile`) is ported. M2.11 and M2.12 close out the M2 milestone by wiring two CLI subcommands to those helpers.
+
+Both subcommands today are reported as "not implemented" by the dispatcher in [go/cmd/fuj/main.go:32-34](../../go/cmd/fuj/main.go#L32). After this change:
+
+- `fuj fees` will compose `domain/fees` with a (stubbed) attendance loader and a fees-table formatter.
+- `fuj reconcile` will compose `domain/reconcile` with stubbed transaction + exception + attendance loaders and a balance-report formatter.
+- Both will exit with a clean, actionable error message until M4 wires real Google Sheets IO behind the loader interfaces.
+
+The user asked to do M2.11 and M2.12 together because they share the same loader scaffolding and formatter package — splitting them would either commit half the package or duplicate work.
+
+## Approach
+
+**One commit, one branch, one MR.** Branch: `feat/m2-11-12-fees-reconcile-cli`. Both M2.11 and M2.12 checkboxes get ticked on merge.
+
+The CLI subcommand is the user-facing layer. It owns nothing. All work lives in a new `services/membership` package: a) loader interfaces, b) the stub implementations that fail with a clear error, c) the orchestration functions, and d) the text formatters. M4 will later add real loader implementations behind the same interfaces — no other code needs to change.
+
+### Package layout
+
+| Path | Contents |
+|---|---|
+| `go/internal/services/membership/doc.go` | Package doc: orchestrates `domain/fees` + `domain/reconcile` against pluggable IO loaders. |
+| `go/internal/services/membership/loader.go` | `AttendanceLoader`, `TransactionLoader`, `ExceptionLoader` interfaces. Aggregate `Sources` interface. `ErrIOPending` sentinel. `NewStubSources()` factory returning a struct that satisfies all three with `ErrIOPending`. |
+| `go/internal/services/membership/fees.go` | `FeesReport(ctx, AttendanceLoader, io.Writer) error` — loads adults, formats, writes. |
+| `go/internal/services/membership/reconcile.go` | `ReconcileReport(ctx, Sources, defaultYear int, io.Writer) error` — loads adults + txns + exceptions, calls `reconcile.Reconcile`, formats, writes. |
+| `go/internal/services/membership/format_fees.go` | `printFeesTable(w, members, sortedMonths)` — fixed-width table mirroring [calculate_fees.py:9-49](../../scripts/calculate_fees.py#L9). |
+| `go/internal/services/membership/format_reconcile.go` | `printReconcileReport(w, result, sortedMonths)` — header / summary table / credits / debts / unmatched / matched-tx detail mirroring [match_payments.py:521-640](../../scripts/match_payments.py#L521). |
+| `go/internal/services/membership/*_test.go` | Table tests for both formatters using fixture data (no IO); separate test confirms `NewStubSources()` returns `ErrIOPending` from each method. |
+| `go/cmd/fuj/main.go` | Add `feesCmd(args)` and `reconcileCmd(args)`. Drop `"fees"` and `"reconcile"` from the not-implemented case (leave `"sync"`, `"infer"`). |
+
+### Public API
+
+```go
+// loader.go
+type AttendanceLoader interface {
+    LoadAdults(ctx context.Context) (members []reconcile.Member, sortedMonths []string, err error)
+}
+type TransactionLoader interface {
+    LoadTransactions(ctx context.Context) ([]reconcile.Transaction, error)
+}
+type ExceptionLoader interface {
+    LoadExceptions(ctx context.Context) (map[reconcile.ExceptionKey]reconcile.Exception, error)
+}
+
+// Sources is the aggregate that fuj reconcile needs.
+type Sources interface {
+    AttendanceLoader
+    TransactionLoader
+    ExceptionLoader
+}
+
+// ErrIOPending is returned by every stub loader method.
+var ErrIOPending = errors.New(
+    "io layer not yet wired up; lands in milestone M4 (sheets/drive/fio)")
+
+func NewStubSources() Sources
+
+// fees.go
+func FeesReport(ctx context.Context, l AttendanceLoader, out io.Writer) error
+
+// reconcile.go
+func ReconcileReport(ctx context.Context, s Sources, defaultYear int, out io.Writer) error
+```
+
+### Loader return types
+
+The interfaces return `domain/reconcile` types directly (`reconcile.Member`, `reconcile.Transaction`, `reconcile.ExceptionKey`, `reconcile.Exception`). These are already shaped for the reconcile algorithm and cover the fees report's needs (`Member.Fees[month].Expected` is precomputed by whatever loader populates it — the Python `get_members_with_fees()` does the same). No translation layer needed; no parallel struct hierarchy.
+
+### Stub implementation pattern
+
+```go
+type stubSources struct{}
+
+func (stubSources) LoadAdults(context.Context) ([]reconcile.Member, []string, error) {
+    return nil, nil, ErrIOPending
+}
+func (stubSources) LoadTransactions(context.Context) ([]reconcile.Transaction, error) {
+    return nil, ErrIOPending
+}
+func (stubSources) LoadExceptions(context.Context) (
+    map[reconcile.ExceptionKey]reconcile.Exception, error) {
+    return nil, ErrIOPending
+}
+
+func NewStubSources() Sources { return stubSources{} }
+```
+
+### Subcommand wiring
+
+```go
+// cmd/fuj/main.go
+case "fees":
+    feesCmd(args)
+case "reconcile":
+    reconcileCmd(args)
+case "sync", "infer":           // keep these in the M4 placeholder
+    fmt.Fprintf(os.Stderr, "fuj %s: not implemented yet (lands in M4)\n", cmd)
+    os.Exit(2)
+
+func feesCmd(args []string) {
+    fs := flag.NewFlagSet("fees", flag.ExitOnError)
+    fs.Usage = func() { fmt.Fprintln(os.Stderr, "usage: fuj fees") }
+    if err := fs.Parse(args); err != nil { ... }
+
+    sources := membership.NewStubSources()
+    ctx := context.Background()
+    if err := membership.FeesReport(ctx, sources, os.Stdout); err != nil {
+        fmt.Fprintf(os.Stderr, "fuj fees: %v\n", err)
+        os.Exit(1)
+    }
+}
+
+func reconcileCmd(args []string) {
+    fs := flag.NewFlagSet("reconcile", flag.ExitOnError)
+    fs.Usage = func() { fmt.Fprintln(os.Stderr, "usage: fuj reconcile") }
+    if err := fs.Parse(args); err != nil { ... }
+
+    sources := membership.NewStubSources()
+    ctx := context.Background()
+    if err := membership.ReconcileReport(ctx, sources, time.Now().Year(), os.Stdout); err != nil {
+        fmt.Fprintf(os.Stderr, "fuj reconcile: %v\n", err)
+        os.Exit(1)
+    }
+}
+```
+
+Both subcommands accept zero positional args today (matching Python `calculate_fees.py` which has none, and skipping the Python `match_payments.py` flags `--sheet-id` / `--credentials` / `--bank` until M4 needs them — no point pre-empting flag design while there's nothing to plumb them into). Update `usage()` in `main.go` to remove the `[M2]` annotations from `fees` / `reconcile`.
+
+### Formatter ports — what to mirror byte-for-byte
+
+The formatters are pure post-processing. Ship them now so M4 only adds real loader plumbing.
+
+**`printFeesTable`** ports [calculate_fees.py:9-49](../../scripts/calculate_fees.py#L9):
+- Filter to `tier == "A"` only.
+- Month label format: `"Jan 2026"` (`time.Parse("2006-01", m).Format("Jan 2006")`).
+- Column widths: `name_width = max(len(name))`, `col_width = 15`.
+- Cell format: `"%d CZK (%d)"` when `count > 0`, else `"-"`. Right-aligned in col_width.
+- Totals row: monthly sums, label `"TOTAL"`, cells `"%d CZK"`.
+- Print "No data." when members is empty.
+
+**`printReconcileReport`** ports [match_payments.py:521-640](../../scripts/match_payments.py#L521):
+- Header banner (`"=" * 80`, "PAYMENT RECONCILIATION REPORT", banner).
+- Per-adult summary table — cell logic: `expected==0 && paid==0 → "-"`, `paid>=expected && expected>0 → "OK"`, `paid>0 → "{paid}/{expected}"`, else `"UNPAID {expected}"`. Balance column: `"+N"` / `"-N"` / `"0"`.
+- TOTAL footer line carrying the `Expected/Paid/Balance` summary.
+- Optional sections: `TOTAL CREDITS` (positive total balances), `TOTAL DEBTS` (negative — print `abs`), `UNMATCHED TRANSACTIONS`, `MATCHED TRANSACTION DETAILS`.
+- Use sorted member-name iteration (`sort.Strings`) — Python uses `sorted(adults.keys())`.
+- Float printing: amounts use `%.0f` (Python `:.0f`), `paid` is cast via `int(...)` before formatting in some places — preserve these (cast to `int` then `%d`).
+
+Tests use a small handcrafted `reconcile.Result` with one paid member, one debtor, one credit, one unmatched tx and assert exact byte equality of the formatted output (golden string in the test source — not file-based).
+
+### Tests
+
+**`format_fees_test.go`**: handcrafted `[]reconcile.Member` covering: tier-filter (J/X excluded), zero-attendance cell, single-attendance cell, multi-attendance cell, empty result → `"No data."`. Golden output strings inline.
+
+**`format_reconcile_test.go`**: handcrafted `reconcile.Result` exercising every branch in the cell logic + each optional section. Golden strings inline. (Don't blindly copy the Python `print(...)` string-formatting bugs — the live Python f-string `f"\n{'TOTAL CREDITS (advance payments or surplus):'}"` is intentional whitespace; reproduce as plain `"\nTOTAL CREDITS (advance payments or surplus):"` and verify identical bytes by running the live Python on the same fixture.)
+
+**`stub_test.go`**: assert each `NewStubSources()` method returns `ErrIOPending` (use `errors.Is`).
+
+**`fees_test.go` / `reconcile_test.go`**: pass a fake loader that returns canned `[]reconcile.Member` / `[]reconcile.Transaction` / exceptions; assert `FeesReport` / `ReconcileReport` write the expected formatter output. This proves the orchestration glues correctly without involving stubs.
+
+Verify formatter golden strings against live Python with one-liner comments at top of each test file, e.g.:
+
+```
+PYTHONPATH=scripts:. python -c '
+from match_payments import print_report
+result = {"members": {...}, "unmatched": [...]}
+print_report(result, ["2026-04"])
+'
+```
+
+## Parity concerns
+
+- **`czech.Normalize` keeps "%" semantics** — exception keys in `reconcile.Reconcile` use `czech.Normalize(name)` and `czech.Normalize(period)`. The `ExceptionLoader` stub doesn't return any, so this isn't exercised in M2.11/M2.12 — but real loaders in M4 must also normalize at load time (matching Python `fetch_exceptions`).
+- **Sorted month iteration** — formatter must respect the `sortedMonths` argument order, not iterate maps directly (Go map iteration is randomized).
+- **Sorted member iteration** — adults sorted by name (`sort.Strings`); Python uses `sorted(adults.keys())` which is byte-order. Czech-diacritic names sort by codepoint either way.
+- **Empty unmatched list** — Python prints nothing; Go must skip the section header when `len(result.Unmatched) == 0`.
+- **`int(paid)` truncation** — Python `int(mdata["paid"])` truncates toward zero. Go `int(float64)` matches. Use `int(paid)` not `math.Round`.
+- **Stub error stable string** — `ErrIOPending.Error()` text is part of the user-facing CLI contract for the duration of M2.11..M3; tests assert `errors.Is`, not the string. Don't change the wording without bumping the changelog.
+- **Default year = `time.Now().Year()`** — `reconcile.Reconcile` needs `defaultYear` for the inference fallback. `time.Now().Year()` matches the Python implicit default for current-year operation. Tests use a fixed year (2026).
+
+## Critical files
+
+- **Read for parity** — [scripts/calculate_fees.py](../../scripts/calculate_fees.py) (full), [scripts/match_payments.py:521-640](../../scripts/match_payments.py#L521), [scripts/match_payments.py:647-684](../../scripts/match_payments.py#L647) (CLI entry shape).
+- **Reuse** — `domain/reconcile.{Member, Transaction, ExceptionKey, Exception, Result, Reconcile}` ([reconcile.go](../../go/internal/domain/reconcile/reconcile.go)), `domain/fees.{CalculateFee, AdultFeeMonthlyRate}` ([fees.go](../../go/internal/domain/fees/fees.go)).
+- **Mirror conventions** — package layout from [go/internal/domain/matching/](../../go/internal/domain/matching/) (one symbol per file, `*_test.go` siblings, top-of-test live-Python verification comments).
+- **New** — `go/internal/services/membership/{doc,loader,fees,reconcile,format_fees,format_reconcile}.go` + `*_test.go`.
+- **Modify** — [go/cmd/fuj/main.go](../../go/cmd/fuj/main.go) (add `feesCmd`/`reconcileCmd`, drop `"fees"`/`"reconcile"` from the M2 not-implemented case, drop `[M2]` annotations from `usage()`).
+
+## Out of scope (explicitly DO NOT touch)
+
+- Real Google Sheets / Drive / Fio loader implementations — M4.1–M4.6.
+- Web routes / handlers — M5.
+- `fuj sync` and `fuj infer` subcommands — M4.7/M4.8.
+- Junior fees report — current Python `make fees` only prints adults; preserve. (`get_junior_members_with_fees` is consumed by the web frontend, not the CLI.)
+- Bank-direct mode (`--bank` flag in [match_payments.py:659](../../scripts/match_payments.py#L659)) — M4 territory.
+- Fixture capture (`tests/fixtures/`) — M3 milestone.
+
+## Verification
+
+1. `cd go && go build ./...` — clean build.
+2. `cd go && go test -race ./internal/services/membership/...` — formatter golden strings match, stub returns `ErrIOPending`, orchestration glues fake loader → formatter correctly.
+3. `cd go && make go-lint` — clean (govet, staticcheck, errcheck, gofumpt, unused).
+4. **End-to-end CLI smoke**:
+   - `make go-build && ./bin/fuj fees` → exits non-zero, stderr contains `"io layer not yet wired up; lands in milestone M4"`.
+   - `./bin/fuj reconcile` → same shape.
+   - `./bin/fuj help` → no longer says `[M2]` next to `fees`/`reconcile`; still says `[M4]` next to `sync`/`infer`.
+5. **Formatter parity spot-check** — pick one fixture (1 adult with 2 months of fees, 1 unmatched tx); run the Python equivalent with the same input; confirm Go output is byte-identical (modulo trailing-whitespace lines — `diff -w` if needed, but aim for clean `diff` first).
+6. Append CHANGELOG entry per [CLAUDE.md](../../CLAUDE.md) (timestamp via `date "+%Y-%m-%d %H:%M %Z"`).
+7. Tick M2.11 and M2.12 in [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](2026-05-03-2349-go-backend-rewrite-progress.md) with the merge SHA. Update the M2 milestone summary line if M2 is now fully closed.
+8. Push branch, open MR via `tea pr create --title "feat(go): wire fuj fees + fuj reconcile (M2.11-12)" --base main --head feat/m2-11-12-fees-reconcile-cli`, print URL, leave merge to user.

docs/plans/2026-05-06-2111-go-m3-fixture-capture.md

@@ -0,0 +1,261 @@
+# M3 — Fixture capture + characterization framework
+
+> On approval: copy this plan to `docs/plans/2026-05-06-2111-go-m3-fixture-capture.md` per [CLAUDE.md](../../srv/personal/fuj-management/CLAUDE.md) plan-location convention.
+
+## Context
+
+The Go rewrite (tracked in [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](../../srv/personal/fuj-management/docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md)) finished M2.1–M2.12 — every pure-domain helper is ported and the `fuj fees` / `fuj reconcile` CLIs are wired. M3 closes the loop: it builds the **parity safety net** that proves Go output matches Python output for every ported function. Without it, M2 is "trust me", and the rewrite has no defensible cutover criterion.
+
+M3 has three deliverables:
+
+1. **A capture pipeline** (`scripts/capture_fixtures.py` + `scripts/scrub_fixtures.py`) that produces deterministic, PII-free JSON fixtures from the live Python implementations.
+2. **A fixture corpus** at [go/tests/fixtures/](../../srv/personal/fuj-management/go/tests/fixtures/) covering the 10 pure functions of M2 (M2.1–M2.9) plus 10 reconcile cases spanning every code path of `reconcile()` (M2.10).
+3. **A parity test runner** in [go/tests/parity/](../../srv/personal/fuj-management/go/tests/parity/) under `//go:build parity` that replays each fixture and asserts byte/value equality against the Go port.
+
+User-confirmed scope decisions:
+- **Single MR** for all six sub-tasks (M3.1–M3.6) — they're tightly coupled; no half-state is committable.
+- **Type envelope only where it matters** — four fields (`generate_sync_id.tx.amount`, `parse_czk_amount.val`, `format_date.val`, `infer_transaction_details.tx.date`) use `{"type":..., "value":...}` to disambiguate int/float/none. Everything else uses raw JSON.
+- **Real seeds for `parse_month_references` and `match_members` only** — read curated message strings from `tmp/payments_transactions_cache.json`, scrub, ship. Other functions stay on handcrafted seeds.
+- **Plan committed at `docs/plans/2026-05-06-2111-go-m3-fixture-capture.md`** — same convention as every M-series predecessor.
+
+## Branch + landing
+
+- Branch: `feat/m3-fixture-capture`. Single MR via `tea pr create`. Tick M3.1–M3.6 on merge with the SHA.
+- No edits to existing Python or Go production code. M3 is purely additive: new scripts, new fixtures, new test files, new Makefile targets, README, CHANGELOG entry, plan archive, progress tracker tick.
+
+## File layout
+
+**Python (capture pipeline):**
+- [scripts/capture_fixtures.py](../../srv/personal/fuj-management/scripts/capture_fixtures.py) — dispatcher CLI; one entry per function via `--func`.
+- [scripts/scrub_fixtures.py](../../srv/personal/fuj-management/scripts/scrub_fixtures.py) — stdin→stdout deterministic bijection scrubber.
+- [scripts/_fixture_seeds.py](../../srv/personal/fuj-management/scripts/_fixture_seeds.py) — internal: handcrafted seeds keyed by `(func, case_id)`, plus the curated real-message extractor.
+
+**Fixture corpus** (committed, PII-free):
+- [go/tests/fixtures/README.md](../../srv/personal/fuj-management/go/tests/fixtures/README.md) — refresh workflow + scrubbing audit guide.
+- `go/tests/fixtures/pure/<func>/<case>.json` — one directory per function (10 functions: `normalize`, `parse_month_references`, `calculate_fee`, `calculate_junior_fee`, `parse_czk_amount`, `generate_sync_id`, `build_name_variants`, `match_members`, `infer_transaction_details`, `format_date`).
+- `go/tests/fixtures/reconcile/<NN>_<case>.json` — 10 numbered reconcile cases.
+
+**Go parity tests** (all under `//go:build parity`):
+- [go/tests/parity/parityio.go](../../srv/personal/fuj-management/go/tests/parity/parityio.go) — shared loader with generic `Case[I,O]` walker, type envelopes mirrored from §3, float tolerance helper.
+- [go/tests/parity/pure/<func>/<func>_parity_test.go](../../srv/personal/fuj-management/go/tests/parity/pure/) — one file per function, ~30 lines each.
+- [go/tests/parity/reconcile/reconcile_parity_test.go](../../srv/personal/fuj-management/go/tests/parity/reconcile/) — bespoke comparator using `math.Abs(got-want) <= 0.01` for `paid` floats, exact equality on int balances.
+
+**Modified:**
+- [Makefile](../../srv/personal/fuj-management/Makefile) — append `go-parity`, `go-test-all`, `capture-fixtures` targets.
+- [CHANGELOG.md](../../srv/personal/fuj-management/CHANGELOG.md) — single entry at top.
+- [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](../../srv/personal/fuj-management/docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md) — tick M3.1–M3.6 with SHA.
+
+## Capture invocation interface
+
+Two-stage pipeline (capture | scrub) so each stage is independently debuggable:
+
+```bash
+python scripts/capture_fixtures.py --func <name> --case <id> --input-seed <id> \
+  | python scripts/scrub_fixtures.py \
+  > go/tests/fixtures/pure/<func>/<id>.json
+```
+
+Capture flags:
+- `--func` — target function (`normalize`, `reconcile`, etc.).
+- `--case` — human-authored case ID, becomes the file stem. Never auto-generated (auto-IDs cause git churn).
+- `--input-seed <id>` — pull from `_fixture_seeds.py` registry (the default mode for handcrafted cases).
+- `--input-stdin` — read a single JSON `{"args":[...], "kwargs":{...}}` doc from stdin (used by the real-message extractor for `parse_month_references` / `match_members`).
+- `--all` — iterate every seed for one function, emit newline-delimited JSON to stdout. Used by the `make capture-fixtures` recipe.
+
+Capture **never writes files**. Output goes to stdout; the caller redirects. The scrubber is always stdin→stdout. Both are pure transforms.
+
+The `make capture-fixtures` target codifies the full refresh workflow. Humans read the target before they read the README.
+
+## Fixture JSON shape (normative)
+
+One JSON object per case:
+
+```json
+{
+  "case": "range_wrap_nov_to_jan",
+  "func": "scripts.czech_utils.parse_month_references",
+  "captured_at": "2026-05-06",
+  "input": { ... },
+  "output": { ... }
+}
+```
+
+`captured_at` is date-only — same-day re-runs produce byte-identical files. No git SHA, no hostname, no time component.
+
+### Per-function input/output schemas
+
+The schema is the **stable contract** between Python capture and Go consumption. Where Python returns heterogeneous types, the capture step pre-translates to the typed shape Go expects.
+
+| Function | Input | Output |
+|---|---|---|
+| `normalize` | `{"text":"…"}` | `{"text":"…"}` |
+| `parse_month_references` | `{"text":"…","default_year":2026}` | `{"months":["2026-01",…]}` |
+| `calculate_fee` | `{"attendance_count":3,"month_key":"2026-02"}` | `{"fee":750}` |
+| `calculate_junior_fee` | `{"attendance_count":1,"month_key":"2026-02"}` | `{"value":0,"unknown":true}` (mirrors `fees.Expected{Value, Unknown}`) |
+| `parse_czk_amount` | `{"val":<envelope>}` | `{"amount":1500.0}` |
+| `generate_sync_id` | `{"tx":{"date":"…","amount":<envelope>,"currency":"CZK","sender":"…","vs":"…","message":"…","bank_id":"…"}}` | `{"sync_id":"<sha256-hex>"}` |
+| `_build_name_variants` | `{"name":"…"}` | `{"variants":["…"]}` |
+| `match_members` | `{"text":"…","member_names":["…"]}` | `{"matches":[{"name":"…","confidence":"auto"}]}` |
+| `infer_transaction_details` | `{"tx":{"sender":"…","message":"…","user_id":"…","date":<envelope>},"member_names":[…],"default_year":2026}` | `{"members":[…],"months":[…],"search_text":"…"}` |
+| `format_date` | `{"val":<envelope>}` | `{"date":"…"}` |
+
+**Type envelope** (used in 4 fields above):
+
+```json
+{"type":"int","value":750}    // distinguishes 750 from 750.0
+{"type":"float","value":750.0}
+{"type":"string","value":"…"}
+{"type":"none"}
+```
+
+The envelope is the answer to the `generate_sync_id` parity risk: Python's `str(750.0) == "750.0"` vs `str(750) == "750"` produces different SHA-256 inputs. JSON natively conflates these; the envelope round-trips them. Go's loader switches on `type` and constructs the matching native value before calling the port.
+
+**`reconcile`** uses raw JSON for everything (its inputs are typed maps/slices already), with one nuance: the `Member.fees[month]` value can be an `int` or a `(fee, count)` tuple per [match_payments.py:339-340](../../srv/personal/fuj-management/scripts/match_payments.py#L339). Capture normalises both to `{"fee":int,"count":int}` so Go side has one shape.
+
+## Scrubber strategy
+
+`scrub_fixtures.py`: stdin → stdout, no state, no salt, no random. Deterministic plain SHA-256. Re-runs are idempotent. Trade-off acknowledged: an attacker with the script can mathematically reverse the mapping. That's fine — the scrubber's job is to keep PII out of git diffs and Claude transcripts, not to defend against an adversary with the source tree.
+
+### Scramble whitelist (only these field keys are scrambled)
+
+`name`, `member_names[]`, `person`, `sender`, `sender_account`, `account`, `vs`, `bank_id`, `user_id`, `note`. Plus a per-document name-substring sweep over `message` strings — applied **before** the field-key walk, because real names show up embedded in message text.
+
+Everything else (dates, amounts, currency, `month_key`, `attendance_count`, `purpose`, `confidence`, `expected`, `paid`, `total_balance`, `fee`, all `YYYY-MM` keys, `match`/`matches` structure) is preserved verbatim. **Whitelist-of-scramble** (not blacklist-of-preserve): when a new field appears, it stays raw until someone explicitly adds it to the list. Fails safe.
+
+### Scrambling functions
+
+- **Names**: `Member_<8hex>` where `<8hex> = sha256(name).hexdigest()[:8]`. Same name → same pseudonym across the whole document and across all fixtures. Stable diffs.
+- **Account numbers** (`[0-9]+/[0-9]{4}`): scramble prefix and bank-suffix separately, preserving length and format.
+- **VS / bank_id / user_id**: digit-string-preserving hash to a same-length numeric token. Non-numeric input → `id_<8hex>`.
+- **Note**: replaced verbatim with `"<scrubbed>"`. Notes are never load-bearing for any test.
+- **Message** (free text): name-sweep applied; rest preserved. Corpus author spot-checks before commit. README §5 documents the audit grep.
+
+## Reconcile fixtures (10 handcrafted cases)
+
+All seeds live in `_fixture_seeds.py` as triples `(members, sorted_months, transactions, exceptions, default_year)`. Capture runs the live Python `reconcile()` and emits canonical JSON; scrubber is a no-op for handcrafted synthetic names but runs anyway for uniformity.
+
+| File | Branch exercised |
+|---|---|
+| `01_greedy_exact.json` | Greedy: amount == sum(expected); zero credit. |
+| `02_greedy_overpayment_credit.json` | Greedy with overflow → credit. |
+| `03_proportional_remainder.json` | Underpayment across 3 months with non-integer split (last month absorbs float remainder per [match_payments.py:421+](../../srv/personal/fuj-management/scripts/match_payments.py#L421)). |
+| `04_even_split_prepayment.json` | All `expected == 0` → even-split fallback. |
+| `05_out_of_window_credit.json` | Month outside `sorted_months` → that share goes to credits, in-window proportional for the rest. |
+| `06_exception_override.json` | Exception entry overrides expected. |
+| `07_other_purpose_split.json` | `purpose="other:tournament"` with two members. |
+| `08_junior_question_mark.json` | Junior with attendance count 1 → `Expected{Unknown:true}`; reconcile reads it as 0 expected. |
+| `09_multiperson_multimonth.json` | `person="Alice, Bob", purpose="2026-01, 2026-02"` → 2x2 fan-out: even-split-by-people then proportional-by-month. |
+| `10_unmatched.json` | Empty `person`, garbage message → goes to `unmatched`. |
+
+The seed registry is the **single source of truth** for these inputs. If Python behaviour drifts intentionally, fixtures regenerate cleanly via `make capture-fixtures`.
+
+## Real-data seeds (for `parse_month_references` and `match_members` only)
+
+`_fixture_seeds.py` reads `tmp/payments_transactions_cache.json` (already gitignored) and selects:
+
+- **`parse_month_references`**: ~15 distinct messages exercising the 45 Czech month declensions, range wraps (`"prosinec-leden"`), year inference, and the `m >= 10 → previous year` heuristic. Selection done once interactively, the chosen indices hardcoded into `_fixture_seeds.py` so re-runs are deterministic. Messages flow through capture (which calls `parse_month_references(msg, default_year=2026)`) then scrubber (name-sweep against the live member roster).
+- **`match_members`**: ~10 distinct `(message, member_names)` pairs exercising auto vs review confidence, common-surname filter, exact-short-circuit. Same pipeline.
+
+**Out of scope for real seeds**: `normalize`, `_build_name_variants`, `reconcile`. These either don't benefit from real data (synthetic exhaustively covers `normalize`, `_build_name_variants`) or have surgical-input requirements that real data can't reliably hit (`reconcile`'s 10 branches).
+
+## Go parity-test layout
+
+One file per function, one Go package per function, mirroring the fixture tree. Each file is short (~30 lines):
+
+```go
+//go:build parity
+
+package normalize_parity_test
+
+import (
+    "fuj-management/go/internal/domain/czech"
+    "fuj-management/go/tests/parity"
+    "testing"
+)
+
+func TestNormalizeParity(t *testing.T) {
+    t.Parallel()
+    parity.RunAll(t, "../../../fixtures/pure/normalize",
+        func(in parity.NormalizeIn) parity.NormalizeOut {
+            return parity.NormalizeOut{Text: czech.Normalize(in.Text)}
+        })
+}
+```
+
+The shared [go/tests/parity/parityio.go](../../srv/personal/fuj-management/go/tests/parity/parityio.go) (also `//go:build parity`) provides:
+
+- `Case[I, O any]` generic loader: walks a fixture directory, decodes each `.json`, returns `(name, input, want)` triples.
+- `RunAll[I, O any](t, dir, fn func(I) O)`: invokes `fn`, compares against `want` with `reflect.DeepEqual` (sorted-slice normalisation for the few sets-cast-to-lists Python returns); for floats uses `math.Abs(got-want) <= 0.01`.
+- One typed `<Func>In` / `<Func>Out` struct pair per function (10 pairs), mirroring §3's JSON shape exactly. Envelope decoder helpers (`AmountEnvelope`, `ValueEnvelope`) live here.
+
+**Reconcile is bespoke** — `reconcile/reconcile_parity_test.go` doesn't use `RunAll` because it needs cell-by-cell tolerant float compare across nested maps. It walks the fixture dir directly.
+
+**Why one-file-per-function** (instead of an umbrella runner): each function lives in a different domain package, so tests must `import` a different package; an umbrella would obscure which package is being checked. Split also enables `go test -tags=parity ./tests/parity/pure/normalize/` to iterate on a single port.
+
+**Why a separate test tree** (instead of co-located parity tests): the M2 unit tests are co-located by convention (e.g. [go/internal/domain/czech/normalize_test.go](../../srv/personal/fuj-management/go/internal/domain/czech/normalize_test.go)). The progress tracker explicitly says fixtures live at `go/tests/fixtures/` and the gate is `go test -tags=parity ./tests/parity/pure/...`. Co-location would scatter fixtures across packages — messy. Separate tree wins.
+
+## Build tag + Makefile
+
+Every parity test file starts with `//go:build parity`. Default `make go-test` excludes them; `make go-parity` runs them:
+
+```makefile
+go-parity:
+	cd $(GO_SRC) && go test -tags=parity ./tests/parity/...
+
+go-test-all: go-test go-parity
+
+capture-fixtures:
+	@bash scripts/capture_all_fixtures.sh    # invokes capture | scrub for every seed
+```
+
+Parity is **not** folded into default `go-test`: keeps the M2 unit-test loop fast, and a missing-fixture failure shouldn't block routine work. CI runs both targets independently so a parity break is a distinct red signal from a unit-test break.
+
+## README content (`go/tests/fixtures/README.md`)
+
+Six sections, ~120 lines:
+
+1. **What's in this tree** — directory map; one line per fixture function explaining what it validates.
+2. **Fixture format** — link to schemas in §3; worked example for `parse_month_references` and one for `reconcile`.
+3. **Refresh workflow** — `make capture-fixtures` regenerates everything; single-file recipe for incremental updates. Always diff before committing.
+4. **When to refresh** — bullet list (schema change, new Czech declension, new fee tier, new reconcile branch). **Do not refresh to "fix" a parity failure** without first proving the Python behaviour is the intended one.
+5. **Verifying scrubbing** — `git diff` should show only `Member_<hex>`-shaped names, `<scrubbed>` notes, structurally-preserved account/VS digits. Audit grep: `git ls-files go/tests/fixtures | xargs grep -l '<your real name>'` should return zero before commit.
+6. **Adding a new fixture** — three steps (add to `_fixture_seeds.py`, run capture, add `In/Out` Go struct fields if needed).
+
+## Parity concerns
+
+- **Float arithmetic in reconcile proportional phase**: ordering-sensitive, may diverge between Python and Go due to FMA. Tolerance `0.01` already in [go/internal/domain/reconcile/reconcile_test.go](../../srv/personal/fuj-management/go/internal/domain/reconcile/reconcile_test.go); parity uses the same tolerance.
+- **Sync-ID float-vs-int stringification**: handled by the envelope (§3). Capture two paired cases per amount value (`amount_750_int.json`, `amount_750_float.json`) so any Go-side conflation surfaces immediately.
+- **NFKD edge cases**: capture set must include rare characters from real names. The handcrafted `normalize` seeds enumerate every distinct character observed in the live member roster (extracted once from `tmp/attendance_regular_cache.json`, hardcoded into `_fixture_seeds.py` as a single-character-per-case sweep).
+- **Czech month declensions**: the real-message seeds for `parse_month_references` cover the wild; handcrafted seeds cover the corner cases (`prosinec-leden` wrap, `m >= 10` heuristic).
+- **Insertion-order determinism in `reconcile`**: Python 3.7+ dict iteration is insertion-ordered; the seed registry preserves order. Go side iterates `sortedMonths` slice explicitly; the parity test verifies this.
+- **`infer_transaction_details` default_year**: Python signature defaults to 2026; capture passes `default_year` as an explicit input. Go side reads it from the fixture.
+
+## Out of scope (explicitly DO NOT touch)
+
+- Real Google Sheets / Drive / Fio loader implementations — M4.1–M4.6.
+- Web routes / handlers — M5.
+- `fuj sync` and `fuj infer` subcommands — M4.7/M4.8.
+- Tier-2 JSON-API parity (`cmd/parity/main.go`) — M5.4.
+- Any change to existing Python code (capture is read-only against the production scripts).
+- Any change to existing Go production code under `go/internal/`.
+
+## Verification
+
+1. `make go-build` — clean build (parity tests excluded by default tag).
+2. `make go-test` — all M2 unit tests still green; no parity test runs.
+3. `make go-parity` — every fixture in `go/tests/fixtures/pure/` and `go/tests/fixtures/reconcile/` deserialises and passes its parity assertion.
+4. `make go-lint` — clean (parity test files lint-clean under `-tags=parity` since `golangci-lint` honours build tags via `.golangci.yml`).
+5. **Capture round-trip**: pick one fixture (e.g. `parse_month_references/range_wrap_nov_to_jan.json`), regenerate via `python scripts/capture_fixtures.py --func parse_month_references --case range_wrap_nov_to_jan --input-seed range_wrap_nov_to_jan | python scripts/scrub_fixtures.py`, confirm byte-identical to the committed file.
+6. **Scrubbing audit**: run the README §5 grep against any name from the live roster — zero hits.
+7. **Reconcile branch coverage**: read each of the 10 reconcile fixture files, confirm the `output` field shows the expected branch (e.g. `02_greedy_overpayment_credit.json` has a non-zero `credits` entry; `04_even_split_prepayment.json` has equal `paid` across all months).
+8. Append CHANGELOG entry per [CLAUDE.md](../../srv/personal/fuj-management/CLAUDE.md) (timestamp via `date "+%Y-%m-%d %H:%M %Z"`).
+9. Tick M3.1–M3.6 in [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](../../srv/personal/fuj-management/docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md) with the merge SHA. Update the M3 milestone summary line if M3 is now fully closed.
+10. Push branch, open MR via `tea pr create --title "feat(go): fixture capture + characterization framework (M3)" --base main --head feat/m3-fixture-capture`, print URL, leave merge to user.
+
+## Critical files
+
+- **Read for parity** — [scripts/czech_utils.py:22](../../srv/personal/fuj-management/scripts/czech_utils.py#L22), [scripts/czech_utils.py:28](../../srv/personal/fuj-management/scripts/czech_utils.py#L28), [scripts/attendance.py:91](../../srv/personal/fuj-management/scripts/attendance.py#L91), [scripts/attendance.py:100](../../srv/personal/fuj-management/scripts/attendance.py#L100), [scripts/infer_payments.py:17](../../srv/personal/fuj-management/scripts/infer_payments.py#L17), [scripts/sync_fio_to_sheets.py:62](../../srv/personal/fuj-management/scripts/sync_fio_to_sheets.py#L62), [scripts/match_payments.py:33](../../srv/personal/fuj-management/scripts/match_payments.py#L33), [scripts/match_payments.py:65](../../srv/personal/fuj-management/scripts/match_payments.py#L65), [scripts/match_payments.py:144](../../srv/personal/fuj-management/scripts/match_payments.py#L144), [scripts/match_payments.py:187](../../srv/personal/fuj-management/scripts/match_payments.py#L187), [scripts/match_payments.py:304](../../srv/personal/fuj-management/scripts/match_payments.py#L304).
+- **Reuse** — `domain/czech.{Normalize, ParseMonthReferences}`, `domain/fees.{CalculateFee, CalculateJuniorFee, Expected}`, `domain/money.ParseCZK`, `domain/synch.GenerateSyncID`, `domain/matching.{BuildNameVariants, MatchMembers, InferTransactionDetails, FormatDate}`, `domain/reconcile.{Member, Transaction, ExceptionKey, Exception, Result, Reconcile}`.
+- **Mirror conventions** — package layout from [go/internal/domain/matching/](../../srv/personal/fuj-management/go/internal/domain/matching/) (one symbol per file, top-of-test provenance comments, `t.Parallel()`, `// [Go]` markers for Go-only cases).
+- **New** — `scripts/{capture_fixtures,scrub_fixtures,_fixture_seeds}.py`; `go/tests/fixtures/README.md` + the corpus; `go/tests/parity/parityio.go` + 10 parity test files + 1 reconcile parity test file.
+- **Modify** — `Makefile` (3 new targets), `CHANGELOG.md` (1 entry), `docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md` (tick M3.1–M3.6).

docs/plans/2026-05-06-2341-go-m4-io-layer.md

@@ -0,0 +1,313 @@
+# Plan: Go rewrite — M4 IO layer behind interfaces
+
+Companion to [2026-05-03-2349-go-backend-rewrite.md](2026-05-03-2349-go-backend-rewrite.md)
+and [2026-05-03-2349-go-backend-rewrite-progress.md](2026-05-03-2349-go-backend-rewrite-progress.md).
+
+## Context
+
+M1–M3 are merged: skeleton + tooling, every pure-domain function ported and
+parity-tested against PII-scrubbed fixtures, and the `fuj fees` / `fuj
+reconcile` subcommands wired but stubbed (`membership.NewStubSources()`
+returns `ErrIOPending` for every loader). M4's job is to replace that stub
+with real IO: read attendance CSVs, read the payments sheet + exceptions
+tab, fetch Drive `modifiedTime` for cache gating, fetch Fio bank
+transactions, and append/update rows on the payments sheet — all behind
+narrow Go interfaces that have in-memory fakes for tests.
+
+Once M4 lands, `fuj fees`, `fuj reconcile`, `fuj sync`, and `fuj infer` all
+work end-to-end against the real Google Sheets and the real Fio account, and
+M5 can start porting the JSON API on top of that IO.
+
+User-confirmed scope choices for this milestone:
+- **No live integration tests.** Fakes-only at unit level; live
+  verification deferred to manual smoke during M7.
+- **Three PRs** (sheets/drive/cache → fio/sync → infer), one per major
+  area, each independently reviewable.
+- **Attendance stays on CSV-via-public-URL** — matches Python, no extra
+  service-account grant needed.
+
+## Approach
+
+### Layering
+
+```
+internal/io/         ← raw, narrow clients (one per external system)
+  sheets/            ← typed wrapper around google.golang.org/api/sheets/v4
+  drive/             ← Drive v3, only ModifiedTime
+  attendance/        ← CSV-via-public-URL fetcher (no auth, no Sheets API)
+  fio/               ← FioClient interface + apiClient + transparentClient
+  cache/             ← FileCache: modifiedTime gate + two-TTL fallback + atomic write
+
+internal/services/membership/   ← already exists; M4 adds adapters that satisfy
+                                  AttendanceLoader / TransactionLoader / ExceptionLoader
+                                  by composing io/sheets + io/drive + io/cache + io/attendance.
+
+internal/services/banksync/     ← new: SyncToSheets (M4.7) + InferPayments (M4.8)
+                                  composing fio + sheets + attendance loaders.
+```
+
+The existing interfaces in [go/internal/services/membership/loader.go](../../go/internal/services/membership/loader.go)
+(`AttendanceLoader`, `TransactionLoader`, `ExceptionLoader`, `Sources`) are
+the seam — M4 adds a `NewSources(cfg config.Config) (Sources, error)`
+constructor next to `NewStubSources()`, and `cmd/fuj/main.go` swaps the
+stub for it.
+
+### Auth — service-account only
+
+Drop the OAuth+`token.pickle` path entirely (the production already uses a
+service account; the fallback only existed because the original Python
+script ran from a developer laptop). Sheets and Drive both authenticate via
+`option.WithCredentialsFile(cfg.CredentialsPath)` plus
+`option.WithScopes(...)`. Single shared `*http.Client` per backend with a
+10s timeout (matches `DRIVE_TIMEOUT`).
+
+### Cache shape
+
+Match Python's wire format so the `tmp/*_cache.json` directory is shared
+safely while both backends run side-by-side:
+
+```json
+{ "modifiedTime": "<RFC3339>", "data": <list|object>, "cachedAt": "<RFC3339>" }
+```
+
+Improvements over Python:
+- Atomic write: marshal → `os.WriteFile(path+".tmp", ..., 0o600)` →
+  `os.Rename`. Python's plain truncate-write stays as-is until M8.
+- The two TTLs (`CacheTTL` and `CacheAPICheckTTL`) live in `config.Config`
+  already; only the `CacheDir` field is new.
+
+The four cache keys mirror Python's `CACHE_SHEET_MAP`:
+`attendance_regular`, `attendance_juniors`, `exceptions_dict`,
+`payments_transactions` → maps to either `AttendanceSheetID` or
+`PaymentsSheetID`.
+
+When Drive fails, fall back to a synthetic key
+`fmt.Sprintf("ttl-5m-%d", time.Now().Unix()/300)` so cache still keys
+deterministically per 5-min bucket (same as Python).
+
+### Fio: two impls behind one interface
+
+```go
+type Client interface {
+    FetchTransactions(ctx context.Context, from, to time.Time) ([]Transaction, error)
+}
+```
+
+`apiClient` (when `cfg.FioAPIToken != ""`) hits
+`https://fioapi.fio.cz/v1/rest/periods/{token}/{from}/{to}/transactions.json`,
+unmarshals via a typed struct, and maps `column0..column22` to fields per
+[scripts/fio_utils.py](../../scripts/fio_utils.py:90). Negative-amount rows
+dropped (matches Python).
+
+`transparentClient` (fallback) GETs
+`https://ib.fio.cz/ib/transparent?a={accountNum}&f={DD.MM.YYYY}&t={DD.MM.YYYY}`
+and walks the response with `golang.org/x/net/html` token visitor, counting
+`<table class="table">` tags and grabbing rows from the **second** one
+(skipping `<thead>`). `bank_id`, `currency`, `user_id`, `sender_account`
+are empty (matches Python — known limitation).
+
+`accountNum` is derived from `cfg.BankAccount` by stripping the IBAN prefix
+(`CZ85 2010 0000 0028 0035 9168` → `2800359168`); add a small helper in
+`config` for this since both the API URL and the transparent URL need it.
+
+### Fakes
+
+In-memory fakes live next to each real impl: `sheets/fake.go`,
+`drive/fake.go`, `fio/fake.go`, `attendance/fake.go`,
+`cache/fake.go` (a passthrough). All exported as `Fake` so tests do
+`sheets.NewFake(rows)` and inject. The membership-adapter tests use these
+fakes plus a couple of new raw-bytes fixtures under
+`go/internal/io/<pkg>/testdata/`:
+
+- `sheets/testdata/payments_minimal.json` — 2D-string array shaped like
+  `values.get` would return.
+- `sheets/testdata/exceptions_minimal.json` — same, for the exceptions tab.
+- `attendance/testdata/adults_minimal.csv` — small adult attendance CSV.
+- `attendance/testdata/juniors_minimal.csv` — small junior CSV.
+- `fio/testdata/api_response.json` — captured Fio API JSON shape.
+- `fio/testdata/transparent.html` — captured transparent-page HTML.
+
+Existing M3 domain fixtures under `go/tests/fixtures/` stay where they are
+and continue to drive parity tests; they aren't reused for IO-layer tests
+because they're at the wrong layer (post-parse domain types).
+
+## Tasks (mapped to tracker)
+
+Same 8 sub-milestones as the tracker, grouped into 3 PRs.
+
+### PR 1 — sheets / drive / cache + membership wiring (M4.1, M4.2, M4.3, M4.6)
+
+1. **Add deps** in [go/go.mod](../../go/go.mod):
+   `google.golang.org/api/{sheets/v4,drive/v3,option}`,
+   `golang.org/x/oauth2/google` (transitively pulled), `golang.org/x/net/html`.
+2. **`internal/io/sheets/`**:
+   - `client.go` — `Client` struct holding `*sheets.Service`; methods
+     `GetValues(ctx, spreadsheetID, a1Range string) ([][]any, error)`,
+     `AppendValues(ctx, spreadsheetID, a1Range string, rows [][]any) error`,
+     `BatchUpdateValues(ctx, spreadsheetID, updates []ValueRange) error`,
+     `SortByColumn(ctx, spreadsheetID, sheetGID int64, columnIndex int) error`.
+   - `fake.go` — exported `Fake` with seedable `Values map[string][][]any`.
+3. **`internal/io/drive/`**:
+   - `client.go` — `Client.ModifiedTime(ctx, fileID string) (string, error)`
+     using `drive.New(...).Files.Get(fileID).Fields("modifiedTime").SupportsAllDrives(true)`.
+   - `fake.go` with seedable `Times map[string]string`.
+4. **`internal/io/attendance/`** (new — public-URL CSV):
+   - `client.go` — `Client.FetchAdults(ctx) ([][]string, error)` and
+     `FetchJuniors(ctx) ([][]string, error)` using `http.Get` on
+     `https://docs.google.com/spreadsheets/d/{ID}/export?format=csv&gid={GID}`,
+     decoded via `encoding/csv`.
+   - Add `AttendanceAdultSheetGID = "0"` constant in `internal/config`.
+5. **`internal/io/cache/`**:
+   - `filecache.go` — `FileCache` with `Get(ctx, key string, fetch func(ctx) (any, error)) (any, error)`
+     wired through `Drive.ModifiedTime` and the two TTL knobs. Atomic write
+     via tmp-file + rename.
+   - Cache key → sheet ID map mirrors Python's `CACHE_SHEET_MAP`.
+6. **`internal/services/membership/sources.go`** (new file in existing
+   package):
+   - `realSources struct { sheets *sheets.Client; drive *drive.Client; attendance *attendance.Client; cache *cache.FileCache }`.
+   - Constructor `NewSources(ctx, cfg) (Sources, error)` builds all clients.
+   - `LoadAdults` reads cached attendance CSV, runs through
+     `domain/fees.CalculateFee` + merged-month logic (port of
+     [scripts/attendance.py](../../scripts/attendance.py:170)
+     `get_members_with_fees`), returns `[]reconcile.Member`.
+   - `LoadTransactions` reads payments sheet rows via cache, parses to
+     `[]reconcile.Transaction` (port of
+     [match_payments.py:208](../../scripts/match_payments.py:208)
+     `fetch_sheet_data`).
+   - `LoadExceptions` reads `'exceptions'!A2:D` via cache, builds
+     `map[ExceptionKey]Exception` (port of `match_payments.py:266`).
+7. **Add `LoadJuniors`** to the `AttendanceLoader` interface (Python infer
+   pulls both adult + junior member lists; needed for M4.8).
+8. **Wire into [cmd/fuj/main.go](../../go/cmd/fuj/main.go)**: replace
+   `membership.NewStubSources()` in `feesCmd` and `reconcileCmd` with
+   `membership.NewSources(ctx, cfg)`.
+9. **Tests** (default tag, no live IO):
+   - `sheets/client_test.go`, `drive/client_test.go`,
+     `cache/filecache_test.go` — exercise fakes + parsing logic with
+     testdata fixtures.
+   - `membership/sources_test.go` — adapter tests with sheets/drive/cache
+     fakes verify CSV→Member, rows→Transaction, exceptions tab → map.
+10. **Config additions**: `CacheDir` (default `tmp` relative to `$PWD`,
+    overridable via `CACHE_DIR` env), `DriveTimeout` (default 10s).
+11. **Manual verification**: `make go-build && go run ./cmd/fuj fees` and
+    `... reconcile` print real reports against the live sheet (with valid
+    `.secret/...credentials.json`).
+12. CHANGELOG entry; tick M4.1, M4.2, M4.3, M4.6 in the progress tracker.
+
+### PR 2 — fio + bank sync (M4.4, M4.5, M4.7)
+
+1. **`internal/io/fio/`**:
+   - `client.go` — `Client` interface, `Transaction` struct.
+   - `api.go` — `apiClient` impl + URL builder + JSON struct definitions
+     for `accountStatement.transactionList.transaction[].column{N}.value`.
+   - `transparent.go` — `transparentClient` impl using
+     `golang.org/x/net/html` token visitor; helper functions
+     `parseCzechAmount` (NBSP/space strip + comma→dot) and
+     `parseCzechDate` (DD.MM.YYYY / DD/MM/YYYY).
+   - `fake.go`.
+   - `New(cfg) Client` chooses impl based on `cfg.FioAPIToken`.
+   - `accountNum(iban)` helper in `internal/config` strips IBAN prefix.
+2. **`internal/services/banksync/sync.go`** (new package):
+   - `SyncToSheets(ctx, cfg, fio Client, sheets *sheets.Client, opts SyncOpts) (added int, err error)`.
+   - Reads existing rows via `sheets.GetValues(... "A1:K")`, validates
+     header against `COLUMN_LABELS`, writes header if missing, builds
+     `existingIDs` from column K (`Sync ID`).
+   - Computes date window: explicit `from`/`to` or `now - days*24h` (default 30d).
+   - For each fetched tx, computes `domain/synch.GenerateSyncID`, skips if
+     present, otherwise builds row in COLUMN_LABELS order with empty
+     manual/person/purpose/inferred slots.
+   - `sheets.AppendValues(... "A2", rows)`.
+   - Optional sort: `sheets.SortByColumn(... gid, 0)` — sheet GID resolved
+     once via `spreadsheets.Get`.
+3. **Wire `fuj sync` subcommand** in `cmd/fuj/main.go`:
+   - Flags: `--days N` (default 30), `--from YYYY-MM-DD`, `--to YYYY-MM-DD`,
+     `--sort` (default true matching `make sync-2026`).
+   - Replace the M4-stub error path.
+4. **Tests** (default tag): `banksync/sync_test.go` with fakes — verify
+   header insertion, dedup against existing sync IDs, multi-row append,
+   sort call.
+5. **Manual verification**: dry-run sync against the real Fio account in a
+   throwaway test sheet; or visually verify `--from --to` window in stdout
+   with a no-write flag (only if cheap to add — otherwise skip per the
+   "no live integration tests" decision).
+6. CHANGELOG entry; tick M4.4, M4.5, M4.7.
+
+### PR 3 — infer (M4.8)
+
+1. **`internal/services/banksync/infer.go`**:
+   - `InferPayments(ctx, cfg, sheets *sheets.Client, attendanceLoader, juniorLoader, opts InferOpts) (updated int, err error)`.
+   - Reads payments sheet `A1:Z` with case-insensitive header lookup.
+   - Required columns: `Person, Purpose, Inferred Amount`. Optional input:
+     `Date, Amount, Sender, Message, VS, manual fix`.
+   - Skip rule (matches [scripts/infer_payments.py:127](../../scripts/infer_payments.py:127)):
+     non-empty `manual fix` OR `Person` OR `Purpose` → leave row alone.
+   - Member list = union of `LoadAdults` + `LoadJuniors` deduped via
+     `domain/matching.CanonicalKey` (already exists from M2).
+   - For each empty row: build tx dict, call
+     `domain/matching.InferTransactionDetails`, prefix `[?] ` if
+     confidence == "review", emit a `ValueRange` update with R1C1 range
+     `R{i}C{personCol+1}:R{i}C{amountCol+1}`.
+   - Single `sheets.BatchUpdateValues` call for all updates.
+2. **Wire `fuj infer` subcommand**: flags `--dry-run` (prints planned
+   updates, no API write).
+3. **Tests** (default tag): `banksync/infer_test.go` — fixture rows,
+   verify skip rule, verify `[?]` prefix on review matches, verify
+   batchUpdate payload shape, verify `--dry-run` is no-op.
+4. CHANGELOG entry; tick M4.8 → milestone gate ✅.
+
+## Critical files
+
+To modify:
+- [go/internal/services/membership/loader.go](../../go/internal/services/membership/loader.go) — add `LoadJuniors` to `AttendanceLoader`, add `NewSources`.
+- [go/cmd/fuj/main.go](../../go/cmd/fuj/main.go) — swap stub for real sources, add `sync`/`infer` subcommands.
+- [go/internal/config/config.go](../../go/internal/config/config.go) — add `CacheDir`, `DriveTimeout`, `AttendanceAdultSheetGID` constant, IBAN→account-num helper.
+- [go/go.mod](../../go/go.mod) / `go.sum` — google APIs + `x/net/html`.
+- [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](2026-05-03-2349-go-backend-rewrite-progress.md) — tick M4.x boxes after each PR.
+- [CHANGELOG.md](../../CHANGELOG.md) — entry per PR.
+
+To create:
+- `go/internal/io/{sheets,drive,attendance,fio,cache}/{client,fake,*_test}.go`
+- `go/internal/io/{sheets,attendance,fio}/testdata/*`
+- `go/internal/services/membership/sources.go` (+ `sources_test.go`)
+- `go/internal/services/banksync/{sync,infer}.go` (+ tests)
+
+## Reused existing helpers
+
+- `domain/fees.CalculateFee` / `CalculateJuniorFee` — fee math (M2.3, M2.4).
+- `domain/matching.{BuildNameVariants,MatchMembers,InferTransactionDetails,FormatDate,CanonicalKey}` — match logic (M2.7–M2.9).
+- `domain/synch.GenerateSyncID` — dedup hash (M2.6).
+- `domain/reconcile.{Member,Transaction,Exception,ExceptionKey}` — domain types.
+- `domain/czech.{Normalize,ParseMonthReferences}` — used inside the
+  attendance/exceptions parsers.
+- `domain/money.ParseCZK` — for parsing transparent-scrape amounts.
+
+## Verification
+
+End-to-end checks once all three PRs land:
+
+1. `make go-build && make go-lint && make go-test` — clean.
+2. `make go-parity` — M3 fixtures still pass (no domain regressions).
+3. `./bin/fuj fees` — prints adult fee report matching Python `make fees`
+   (visual diff acceptable for now; byte-equality enforced in M5).
+4. `./bin/fuj reconcile` — prints balance report comparable to
+   [scripts/match_payments.py](../../scripts/match_payments.py) `print_balance_report`.
+5. `./bin/fuj sync --days 7` — appends new Fio rows to the payments sheet
+   (run with a real but recent date window; verify by counting added rows
+   and confirming no duplicates on a second run).
+6. `./bin/fuj infer --dry-run` — prints planned Person/Purpose/Inferred
+   Amount updates without modifying the sheet. Then `./bin/fuj infer`
+   applies them; second run is a no-op (skip rule).
+7. **Cache check**: delete `tmp/*_cache.json`, run `fuj fees`, verify file
+   appears with `modifiedTime` matching Drive. Re-run within 5 min;
+   verify no Drive call (debug log).
+8. **Cross-process cache safety**: while `make web-py` is running, run
+   `fuj reconcile`; verify Python's cache file isn't corrupted and Go
+   reads the same data.
+
+Gate (per tracker):
+> `go test -tags=integration ./internal/io/...` round-trips against test sheet; default-tag tests run on fakes.
+
+Per the user's scope decision, **the integration-test gate is downgraded
+to "default-tag tests on fakes" only**. Live verification is deferred to
+manual smoke during M7's parallel-run watch period. The progress tracker's
+M4 gate line will be amended in PR 1.

docs/plans/2026-05-07-1033-fuj-sync-dry-run.md

@@ -0,0 +1,36 @@
+# Plan: add `--dry-run` to `fuj sync`
+
+## Context
+
+`fuj infer` already supports `--dry-run` (it builds the planned `BatchUpdateValues`
+operations, prints them, and skips the actual write — see
+`go/internal/services/banksync/infer.go:136-156` and the
+`Dry run: would update N row(s).` line in `go/cmd/fuj/main.go:209-213`).
+
+`fuj sync` had no equivalent. It always committed three potential writes to the
+payments sheet: `WriteHeader` (if the header row is missing/wrong), `AppendValues`
+(for each new Fio transaction), and `SortByDateColumn` (if `--sort`, default true).
+For inspecting what a sync *would* do — useful when debugging dedupe, sanity-checking
+a date window, or wiring up the command for the first time on a new account — the
+only options were pointing at a throwaway spreadsheet or reading the diff after the fact.
+
+This change mirrors `infer`'s read-only mode for `sync`: same flag name, same output
+style, same "build the data structures, print instead of writing" shape.
+
+## Files modified
+
+1. `go/internal/services/banksync/sync.go` — `DryRun bool` field added to `SyncOpts`; three write points gated on `opts.DryRun`
+2. `go/cmd/fuj/main.go` — `--dry-run` flag added to `syncCmd`; final println split on `*dryRun`
+3. `go/internal/services/banksync/sync_test.go` — `TestSyncToSheets_DryRun` added
+4. `CHANGELOG.md` — entry added
+
+## Behaviour
+
+When `--dry-run` is set:
+
+- If the sheet header is missing/wrong → prints `Dry run: would write header row`; skips `WriteHeader`
+- For each non-deduped Fio transaction → prints `Dry run: would append date=… amount=… sender=… vs=… message=…`; skips `AppendValues`
+- If `--sort` is true → prints `Dry run: would sort by date`; skips `SortByDateColumn`
+- Returns `len(newRows)` so the caller can print `Dry run: would sync N new transaction(s).`
+
+The existing ID-dedup logic runs in full even during dry-run (reads the sheet, builds `existingIDs`), so the output reflects exactly what the next real sync would do.

docs/plans/2026-05-07-1321-fuj-sync-print-fio-table.md

@@ -0,0 +1,29 @@
+# Add `--print-fio-table` debug flag to `fuj sync`
+
+## Context
+
+The Go port of `fuj sync --dry-run` currently prints only the **new**
+transactions — i.e. rows that will be appended to the payments sheet after
+deduping against existing Sync IDs (see [sync.go:125-129](../../go/internal/services/banksync/sync.go#L125-L129)).
+When debugging Fio sync issues ("why isn't transaction X showing up?",
+"is the dedup working?"), there's no way to see what Fio actually
+returned versus what got filtered as a duplicate.
+
+This change adds a `--print-fio-table` flag that, **only when combined
+with `--dry-run`**, prints an aligned table of every Fio transaction in
+the window with each row marked `NEW` (would be appended) or `DUP`
+(already in sheet, skipped). The flag is silently ignored without
+`--dry-run`, so it can't accidentally fire during a real sync.
+
+## Decisions
+
+- Flag name: `--print-fio-table` (specific, not generic `--verbose`).
+- Columns: `DATE | AMOUNT | SENDER | VS | MESSAGE | BANKID | STATUS`,
+  with MESSAGE truncated and STATUS = `NEW` / `DUP`.
+- Scope: only effective when `--dry-run` is also set.
+
+## Files modified
+
+- [go/cmd/fuj/main.go](../../go/cmd/fuj/main.go) — new flag + SyncOpts field
+- [go/internal/services/banksync/sync.go](../../go/internal/services/banksync/sync.go) — SyncOpts struct + refactored step 4
+- [go/internal/services/banksync/debug.go](../../go/internal/services/banksync/debug.go) — printFioTable helper (new)

docs/plans/2026-05-07-1431-m5-json-api-parity.md

@@ -0,0 +1,185 @@
+# Python view-model cleanup (M5 prep — Python side only)
+
+Scoped-down precursor to M5 of the Go rewrite. See:
+- [2026-05-03-2349-go-backend-rewrite.md](2026-05-03-2349-go-backend-rewrite.md)
+- [2026-05-03-2349-go-backend-rewrite-progress.md](2026-05-03-2349-go-backend-rewrite-progress.md)
+
+## Context
+
+The Python app is still production. Before adding `/api/X` shadow
+routes, JSON DTOs, parity tooling, and Go handlers, get the Python
+side into a clean shape. Today the `/adults` and `/juniors` routes
+each carry 150–200 lines of inline view-model construction inside
+the Flask handler:
+
+- [adults_view](app.py#L179) — 167 LOC, computes per-row
+  status/cell_text/balance/credits/debts inline.
+- [juniors_view](app.py#L347) — 205 LOC, same plus `"?"` sentinel
+  branching and `:NJ,MA` breakdown.
+- [payments](app.py#L553) — 35 LOC, lighter but still mixes IO and
+  grouping.
+
+Pulling that into pure builder functions:
+- shrinks `app.py` and makes each route handler do only what a route
+  handler should (IO + cache + step timing + render);
+- gives us **already-tested** pure functions that future M5 work can
+  call from a `/api/X` shadow endpoint with one line of `jsonify(...)`;
+- has zero behavioural change (existing tests in
+  [test_app.py](tests/test_app.py) act as the regression guard).
+
+This is a Python-only change. No Go work, no JSON contract, no shadow
+routes — those come after.
+
+## Approach
+
+Three pure builder functions in a new `scripts/views.py` module. Each
+takes already-loaded, deserialized inputs (no Flask globals, no IO,
+no cache calls) and returns the exact dict that today's route passes
+to `render_template`.
+
+```python
+def build_adults_view_model(
+    members, sorted_months, transactions, exceptions, current_month,
+    *, attendance_url, payments_url, bank_account,
+) -> dict: ...
+
+def build_juniors_view_model(
+    junior_members, sorted_months, transactions, exceptions, current_month,
+    *, attendance_url, payments_url, bank_account,
+) -> dict: ...
+
+def build_payments_view_model(
+    transactions, member_names,
+    *, attendance_url, payments_url,
+) -> dict: ...
+```
+
+The route handlers shrink to: load data (with `get_cached_data` and
+`record_step` calls staying in `app.py`), call the builder, render.
+
+```python
+@app.route("/adults")
+def adults_view():
+    members, sorted_months = ... # cached loads + record_step calls
+    transactions = ...
+    exceptions = ...
+    result_meta = ...
+    record_step("process_data")
+    vm = build_adults_view_model(
+        members, sorted_months, transactions, exceptions,
+        datetime.now().strftime("%Y-%m"),
+        attendance_url=..., payments_url=..., bank_account=BANK_ACCOUNT,
+    )
+    return render_template("adults.html", **vm)
+```
+
+## Decisions
+
+1. **Pure builders, no Flask state.** No `record_step`, no `g.*`, no
+   `get_cached_data` inside builders. They take plain args, return
+   plain dicts. This is what makes them trivially unit-testable and,
+   later, trivially reusable from `/api/X`.
+2. **Preserve byte-equal behaviour.** The dicts returned must match
+   today's `render_template(...)` kwargs key-for-key, value-for-value
+   — including the existing `json.dumps(member_data)` /
+   `json.dumps(month_labels_json)` / `json.dumps(raw_payments_json)`
+   wrappers. Those wrappers exist for inline JS in templates; the
+   refactor doesn't touch them. (When `/api/X` lands later, that route
+   will produce a sibling dict with the wrappers stripped, but that's
+   future work.)
+3. **`reconcile()` stays inside the route, not the builder.** It
+   crosses the IO/cache boundary in spirit (its inputs come from
+   cache); but it's also pure-domain and called by both adults and
+   juniors. Keep the call site in the route so `record_step("reconcile")`
+   timing isn't lost. Builder takes `result` as an argument.
+4. **Shared helpers stay in `app.py`** for now —
+   [get_month_labels](app.py#L41) and
+   [group_payments_by_person](app.py#L60) are already module-level
+   pure functions, used by routes and now by builders. Either leave
+   them in `app.py` and import into `scripts/views.py`, or move them
+   into `scripts/views.py`. **Choose: move into `scripts/views.py`**
+   — they're view-model concerns, not Flask concerns, and `app.py`
+   should keep shrinking.
+5. **No new test file needed.** Existing
+   [tests/test_app.py](tests/test_app.py) tests
+   `test_adults_route`, `test_juniors_route`, `test_payments_route`
+   exercise the rendered HTML end-to-end. If they pass after the
+   refactor, behaviour is preserved. Adding builder-level unit tests
+   is a *nice-to-have* but not required for this iteration.
+
+## Tasks
+
+### 1. Create `scripts/views.py` with the three builders + shared helpers
+
+- Move `get_month_labels` and `group_payments_by_person` from
+  [app.py:41–77](app.py#L41-L77) into `scripts/views.py`. Update the
+  import in `app.py`.
+- Implement `build_adults_view_model` by extracting
+  [app.py:200–344](app.py#L200-L344) (everything between `result =
+  reconcile(...)` and `return render_template(...)`). Take `result`
+  as a parameter; emit the same dict that's currently passed as
+  `**kwargs` to `render_template`.
+- Implement `build_juniors_view_model` by extracting
+  [app.py:370–550](app.py#L370-L550). Same shape — including the
+  `adapted_members` adapter loop, the junior `?`-sentinel branches,
+  and the `:NJ,MA` breakdown.
+- Implement `build_payments_view_model` by extracting
+  [app.py:570–586](app.py#L570-L586) (the `group_payments_by_person`
+  call + `Unmatched / Unknown` bucket + sort).
+
+### 2. Slim down the route handlers in `app.py`
+
+Each handler keeps:
+- `attendance_url`/`payments_url` URL building
+- `get_cached_data` calls (with `record_step` between)
+- `reconcile(...)` call (adults/juniors) with `record_step("reconcile")`
+- `record_step("process_data")` after the builder call
+- `return render_template("X.html", **view_model)`
+
+Each handler **drops** all the per-row computation, totals
+formatting, credits/debts sorting, `raw_payments_by_person` building,
+and `import json` lines.
+
+Target post-refactor LOC for each route handler: ~25–30 lines
+(currently 167 / 205 / 35).
+
+### 3. Run the existing test suite + manual smoke
+
+```
+make test                # all tests green
+make web-py              # browse /adults /juniors /payments visually
+```
+
+## Critical files
+
+- [app.py](app.py) — routes shrink dramatically; `get_month_labels`
+  and `group_payments_by_person` get moved out.
+- New: `scripts/views.py` — three builders + the two helpers.
+- [tests/test_app.py](tests/test_app.py) — unchanged; serves as the
+  regression guard.
+
+## Verification
+
+1. `make test` — all four `TestWebApp` tests pass unchanged.
+2. `make web-py` and visit `/adults`, `/juniors`, `/payments` — each
+   renders identically to before (same table contents, same totals,
+   same credits/debts, same `?` rendering on juniors).
+3. `git diff app.py` shows substantial deletions (route bodies
+   shrink) and only thin glue calling the new builders.
+4. Optional sanity check: temporarily add `print(repr(view_model))`
+   in the route before `render_template` on `main` and on the branch,
+   diff for one fixture run — should be byte-identical dicts.
+
+## Out of scope (future iterations, not this plan)
+
+- `/api/<route>` shadow endpoints in Flask
+- Go `internal/web/api/` DTOs and JSON Schemas
+- Go `internal/services/membership/views.go` aggregators
+- Go HTTP handlers for `/api/X`
+- `cmd/parity/main.go` and `make parity` target
+- Junior breakdown sidecar work in
+  `go/internal/services/membership/sources.go`
+
+These are the original M5 tasks (M5.1–M5.4 in the progress tracker).
+They become much easier once today's refactor lands, because the
+shadow `/api/X` routes will be one-liners over the new builders.

docs/plans/2026-05-07-1650-go-rewrite-m5-1-api-structs-schemas.md

@@ -0,0 +1,240 @@
+# M5.1 — Hand-author Go API structs + emit JSON Schemas
+
+Companion to:
+- [2026-05-03-2349-go-backend-rewrite.md](2026-05-03-2349-go-backend-rewrite.md) (master design)
+- [2026-05-03-2349-go-backend-rewrite-progress.md](2026-05-03-2349-go-backend-rewrite-progress.md) (progress tracker — M5.1 row)
+- [2026-05-07-1431-m5-json-api-parity.md](2026-05-07-1431-m5-json-api-parity.md) (Python view-model extraction prep — already merged as `b562ce3` / `32a16ff` / `59223c0`)
+
+## Context
+
+M4 (IO layer behind interfaces) just landed. M5 is the JSON-parity contract phase — byte-equal JSON between Python and Go for `/api/adults`, `/api/juniors`, `/api/payments`, `/api/version`. Within M5, the work splits four ways:
+
+- **M5.1 — this plan.** Define the wire contract: hand-authored Go structs with explicit `json:` tags matching Python keys, plus committed JSON Schemas generated by `github.com/invopop/jsonschema`. **Schemas only — no handlers, no Python `/api/X` routes, no parity tool.**
+- M5.2 — Implement Go handlers that compose `services/*` results into these structs.
+- M5.3 — Add Python `/api/X` shadow endpoints in [app.py](app.py).
+- M5.4 — `cmd/parity/main.go` + `make parity` target.
+
+The recent Python view-model extraction (`scripts/views.py`) lays the groundwork: every Python builder now returns a plain dict that an `/api/X` shadow can `jsonify` (with one minor unwrap step — see decision #1 below). M5.1 is the matching Go side: types and schemas that pin down the contract before any code writes JSON to a wire.
+
+## Key design decisions
+
+1. **Wire format is nested objects, not strings-of-JSON.** The Python view-model dicts contain three template-only fields that are pre-serialized JSON strings: `member_data`, `month_labels_json`, `raw_payments_json`. Those exist purely to feed inline `<script>` blocks in Jinja templates ([scripts/views.py:227-237](scripts/views.py#L227-L237)). The `/api/X` JSON contract uses the **un-stringified** nested form. Rationale:
+   - The master design doc references `total_balance`, `original_expected`, `attendance_count` as struct fields ([2026-05-03-2349-go-backend-rewrite.md:223-225](docs/plans/2026-05-03-2349-go-backend-rewrite.md#L223-L225)), which are *inside* `member_data` — only meaningful if it's a nested object.
+   - The `Expected` `MarshalJSON` design (emit `42` or `"?"`) ([same doc:233-238](docs/plans/2026-05-03-2349-go-backend-rewrite.md#L233-L238)) only fires inside `member_data`; pointless if that field is a string.
+   - Strings-of-JSON make `invopop/jsonschema` schemas useless for those fields (`{"type": "string"}` describes nothing).
+   - The Python prep plan ([2026-05-07-1431-m5-json-api-parity.md:87-89](docs/plans/2026-05-07-1431-m5-json-api-parity.md#L87-L89)) already anticipates this: "that route will produce a sibling dict with the wrappers stripped".
+
+   This refines (does not contradict) M5.3's "no transformation" wording. M5.3's `/api/X` will be `jsonify(unwrap_json_strings(view_model_dict))` — a 4-line shim, not real transformation logic.
+
+2. **New package: `internal/web/api/`.** The Go side has no `api/` package today — only [internal/web/server.go](go/internal/web/server.go) with one hello route. The api package owns wire types and (in M5.2) handlers. Sub-files per route keep diffs small.
+
+3. **Wire types are separate from `domain/reconcile.Result`.** [domain/reconcile/reconcile.go:88-92](go/internal/domain/reconcile/reconcile.go#L88-L92) defines `Result`, `MemberResult`, `MonthData`, `TxEntry`, etc. — none have `json:` tags. **Don't tag the domain types**: that bleeds wire concerns into pure logic and locks the JSON contract to internal field names. Define wire types in `internal/web/api/` and convert in M5.2's handlers.
+
+4. **`Expected{Value int; Unknown bool}` with custom `MarshalJSON`/`UnmarshalJSON`** for junior `expected` and `original_expected`. Already prescribed by the master design.
+
+5. **Transaction `amount` / `inferred_amount` may be `int` or `""`** (Sheets `UNFORMATTED_VALUE` returns empty string for blank cells per `scripts/match_payments.py` rows 250-260 in the views.py exploration). Use a custom `SheetsNumber` type with `MarshalJSON`/`UnmarshalJSON` that emits `0`/`null` for empty and the number otherwise. Document in code comment with a one-liner. Verify exact behavior by inspecting one or two existing scrubbed reconcile fixtures before coding.
+
+6. **Schema generation lives in `internal/web/api/schemagen_test.go`** with `-update` flag, à la golden tests. Default test run (`go test ./internal/web/api/...`) re-generates schemas in memory and asserts byte-equality vs the committed files in `tests/fixtures/api-schema/`. `go test -update ./internal/web/api/...` rewrites the committed files. Avoids a separate `cmd/gen-api-schema` binary; CI catches drift automatically.
+
+7. **One schema per route**, named to match the Go type:
+   ```
+   go/tests/fixtures/api-schema/adults.schema.json
+   go/tests/fixtures/api-schema/juniors.schema.json
+   go/tests/fixtures/api-schema/payments.schema.json
+   go/tests/fixtures/api-schema/version.schema.json
+   ```
+
+8. **Adults and Juniors are *not* the same type.** Their outer shapes match (same keys), but `MonthCell.Text` semantics differ (juniors render `"?"`, `"?(3)"`, `:NJ,MA` breakdowns) and `member_data` semantics differ (juniors carry `Expected` sentinel). Define `AdultsResponse` and `JuniorsResponse` separately even if they share most field types — clearer schemas and easier to evolve independently. Share scalar types (`Transaction`, `Exception`, `MonthCell`, `TotalCell`) in `types.go`.
+
+9. **Money is integer CZK** ([master design:55-56](docs/plans/2026-05-03-2349-go-backend-rewrite.md#L55-L56)). All amount fields use `int`. The one exception: `member_data[name].months[YYYY-MM].paid` is a `float64` in the Python output (proportional allocation produces fractional CZK like `33.333333`). Use `float64` only there; document the why in a one-line comment.
+
+## Files to create
+
+```
+go/internal/web/api/
+├── types.go             # SheetsNumber, Expected, Exception, Transaction, MonthCell, TotalCell, MemberRow
+├── adults.go            # AdultsResponse + adults-specific MemberData
+├── juniors.go           # JuniorsResponse + juniors-specific MemberData (with Expected fields)
+├── payments.go          # PaymentsResponse
+├── version.go           # VersionResponse
+└── schemagen_test.go    # generates + golden-asserts schemas
+
+go/tests/fixtures/api-schema/
+├── adults.schema.json
+├── juniors.schema.json
+├── payments.schema.json
+└── version.schema.json
+```
+
+## Struct skeleton (illustrative, not final wording)
+
+```go
+// internal/web/api/types.go
+
+// SheetsNumber wraps a value that may arrive from Google Sheets as either
+// a JSON number or "" (empty string for blank cells). Marshals as 0 when
+// missing; the consumer treats Missing+Value=0 as "no data".
+type SheetsNumber struct {
+    Value   float64
+    Missing bool
+}
+
+// Expected carries a junior's expected fee or the "?" sentinel
+// (single-attendance month requires manual review).
+type Expected struct {
+    Value   int
+    Unknown bool
+}
+
+type Exception struct {
+    Amount int    `json:"amount"`
+    Note   string `json:"note"`
+}
+
+type Transaction struct {
+    Date           string       `json:"date"`
+    Amount         SheetsNumber `json:"amount"`
+    ManualFix      string       `json:"manual_fix"`
+    Person         string       `json:"person"`
+    Purpose        string       `json:"purpose"`
+    InferredAmount SheetsNumber `json:"inferred_amount"`
+    Sender         string       `json:"sender"`
+    Message        string       `json:"message"`
+    BankID         string       `json:"bank_id"`
+}
+
+type MonthCell struct {
+    Text       string `json:"text"`
+    Overridden bool   `json:"overridden"`
+    Status     string `json:"status"` // "empty"|"ok"|"partial"|"unpaid"|"surplus"
+    Amount     int    `json:"amount"`
+    Month      string `json:"month"`      // display label, e.g. "Apr+May 2025"
+    RawMonth   string `json:"raw_month"`  // YYYY-MM
+    Tooltip    string `json:"tooltip"`
+}
+
+type TotalCell struct {
+    Text   string `json:"text"`
+    Status string `json:"status"`
+}
+
+type MemberRow struct {
+    Name              string      `json:"name"`
+    Months            []MonthCell `json:"months"`
+    Balance           int         `json:"balance"`
+    UnpaidPeriods     string      `json:"unpaid_periods"`
+    RawUnpaidPeriods  string      `json:"raw_unpaid_periods"`
+    PayableAmount     int         `json:"payable_amount"`
+}
+
+type Credit struct {
+    Name   string `json:"name"`
+    Amount int    `json:"amount"`
+}
+```
+
+```go
+// internal/web/api/adults.go
+type AdultsMonthData struct {
+    Status      string             `json:"status"`
+    Expected    int                `json:"expected"`
+    Paid        float64            `json:"paid"` // float — proportional allocator can produce 33.333…
+    Exception   *Exception         `json:"exception"`
+    AmountToPay int                `json:"amount_to_pay"`
+    // ... transactions, others, etc — match exact keys from result["members"][name]["months"][YYYY-MM]
+}
+
+type AdultsMemberData struct {
+    TotalBalance int                          `json:"total_balance"`
+    Months       map[string]AdultsMonthData   `json:"months"` // YYYY-MM key
+    Transactions []Transaction                `json:"transactions"`
+}
+
+type AdultsResponse struct {
+    Months          []string                    `json:"months"`
+    RawMonths       []string                    `json:"raw_months"`
+    Results         []MemberRow                 `json:"results"`
+    Totals          []TotalCell                 `json:"totals"`
+    MemberData      map[string]AdultsMemberData `json:"member_data"`
+    MonthLabels     map[string]string           `json:"month_labels"`     // was month_labels_json (string)
+    RawPayments     map[string][]Transaction    `json:"raw_payments"`     // was raw_payments_json (string)
+    Credits         []Credit                    `json:"credits"`
+    Debts           []Credit                    `json:"debts"`
+    Unmatched       []Transaction               `json:"unmatched"`
+    AttendanceURL   string                      `json:"attendance_url"`
+    PaymentsURL     string                      `json:"payments_url"`
+    BankAccount     string                      `json:"bank_account"`
+    CurrentMonth    string                      `json:"current_month"`
+}
+```
+
+`JuniorsResponse` mirrors `AdultsResponse` but the inner `MonthData` carries `Expected` and `OriginalExpected` (both `Expected` type), and adds the `:NJ,MA` breakdown fields produced by [scripts/views.py:290-298](scripts/views.py#L290-L298).
+
+`PaymentsResponse`:
+
+```go
+type PaymentsResponse struct {
+    GroupedPayments map[string][]Transaction `json:"grouped_payments"`
+    SortedPeople    []string                 `json:"sorted_people"`
+    AttendanceURL   string                   `json:"attendance_url"`
+    PaymentsURL     string                   `json:"payments_url"`
+}
+```
+
+`VersionResponse` mirrors Python's `BUILD_META` ([app.py:67](app.py#L67)):
+
+```go
+type VersionResponse struct {
+    Tag       string `json:"tag"`
+    Commit    string `json:"commit"`
+    BuildDate string `json:"build_date"`
+}
+```
+
+Exact fields inside the per-month `MonthData`/`MemberData` will be finalized by inspecting **one** scrubbed `member_data` JSON dump from a current `/adults` and `/juniors` call (see Verification step 1) — names and types have to be identical.
+
+## Reusable existing code
+
+- `domain/reconcile.Result` ([go/internal/domain/reconcile/reconcile.go:88](go/internal/domain/reconcile/reconcile.go#L88)) — source data for adults/juniors. M5.2 maps it to wire types; M5.1 only needs to know the field set.
+- `web.BuildInfo` ([go/internal/web/server.go:11-15](go/internal/web/server.go#L11-L15)) — already wired through `cmd/fuj/main.go:79`. The `VersionResponse` type is a thin renaming of this with json tags. Decide in M5.2 whether to *also* tag `BuildInfo` directly (it's not really domain) or keep `VersionResponse` separate. M5.1 just defines the wire struct.
+- `scripts/views.py` builders — the spec for every key/type. Treat as authoritative.
+
+## Tasks
+
+1. **Add `github.com/invopop/jsonschema` dependency.** `cd go && go get github.com/invopop/jsonschema && go mod tidy`. Single commit.
+2. **Capture one fresh `member_data` dump for adults and juniors** to pin down inner-dict field names and types precisely (especially `paid` precision, `transactions[]` shape, `others[]` if present). Run `make web-py` on a known-good cache, hit `/adults` and `/juniors`, dump `view_model["member_data"]` to a scratch file (gitignored), and inspect. **Do not commit raw dumps** — PII rule. This is for shape inspection only.
+3. **Author `internal/web/api/types.go`** with `SheetsNumber`, `Expected`, `Exception`, `Transaction`, `MonthCell`, `TotalCell`, `MemberRow`, `Credit`. Implement `MarshalJSON`/`UnmarshalJSON` for `SheetsNumber` and `Expected`. Use struct tags `json:"snake_case_key"` matching Python exactly.
+4. **Author `internal/web/api/adults.go`** with `AdultsMonthData`, `AdultsMemberData`, `AdultsResponse`. Cross-check every key against the dump from step 2.
+5. **Author `internal/web/api/juniors.go`** similarly, with `Expected` fields and the J/A breakdown.
+6. **Author `internal/web/api/payments.go` and `version.go`** (small).
+7. **Author `internal/web/api/schemagen_test.go`** that:
+   - Imports `github.com/invopop/jsonschema`.
+   - Defines a `schemaCases` slice: `{name: "adults", typ: AdultsResponse{}, ...}` etc.
+   - For each case, generates a schema, marshals indented JSON, compares against committed file at `../../tests/fixtures/api-schema/<name>.schema.json`.
+   - Honors a `-update` flag (`flag.Bool`) that rewrites the committed file instead of asserting.
+   - One `t.Run(case.name, ...)` per route for clear failure output.
+8. **Run with `-update` once to populate** `tests/fixtures/api-schema/*.schema.json`. Eyeball each schema: required fields list, oneOf for `Expected`, additionalProperties on map types. Commit.
+9. **Lint + test:** `cd go && go vet ./... && make go-test && make go-lint`. Fix any issues. (Expect zero — this is read-only data structures.)
+10. **CHANGELOG entry** + tick `M5.1` in [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md:100](docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md#L100) with the merge SHA.
+11. **Branch + MR per CLAUDE.md workflow:** branch `feat/go-m5-1-api-structs`, push with `-u`, open MR via `tea pr create`. Do not merge from CLI.
+
+## Verification
+
+1. `cd go && go test ./internal/web/api/...` — **schemas regenerate identically** to committed files.
+2. `cd go && go test ./internal/web/api/... -update` then `git diff go/tests/fixtures/api-schema/` — diff is empty (idempotent generation).
+3. `cd go && make go-lint` — clean.
+4. `cd go && go vet ./...` — clean.
+5. Manual schema inspection: open `adults.schema.json`, confirm:
+   - Top-level `required` list contains every Python key.
+   - `member_data` is `additionalProperties: { ... AdultsMemberData ... }` (a map keyed by name).
+   - `expected` and `original_expected` (juniors only) are `oneOf: [{type: integer}, {const: "?"}]`.
+   - `amount` and `inferred_amount` on `Transaction` accept number or empty/null.
+6. **No production code paths exercised yet** — handlers come in M5.2. Compile-time success + schema golden-test = M5.1 done.
+
+## Out of scope (later M5 tasks)
+
+- Wiring Go HTTP handlers for `/api/X` (M5.2).
+- Adding Python `/api/X` shadow endpoints (M5.3) — including the `unwrap_json_strings(view_model)` shim noted in design decision #1.
+- `cmd/parity/main.go` and `make parity` target (M5.4).
+- Tagging `domain/reconcile.Result` with `json:` tags — explicitly avoided.
+- Refactoring the strings-of-JSON fields out of the Python view-model — they stay in `views.py` for the template path, the `/api/X` shadow unwraps them.

docs/plans/2026-05-07-2114-go-rewrite-m5-3-python-api-shadow.md

@@ -0,0 +1,113 @@
+# M5.3 — Python `/api/X` shadow endpoints
+
+Companion to:
+- [2026-05-03-2349-go-backend-rewrite.md](2026-05-03-2349-go-backend-rewrite.md) (master design)
+- [2026-05-03-2349-go-backend-rewrite-progress.md](2026-05-03-2349-go-backend-rewrite-progress.md) (M5.3 row)
+- [2026-05-07-1431-m5-json-api-parity.md](2026-05-07-1431-m5-json-api-parity.md) (Python view-model extraction prep)
+- [2026-05-07-1650-go-rewrite-m5-1-api-structs-schemas.md](2026-05-07-1650-go-rewrite-m5-1-api-structs-schemas.md) (Go wire types)
+
+## Context
+
+M5.1 (Go wire types + JSON Schemas) and M5.2 (Go HTTP handlers for `/api/adults` `/api/juniors` `/api/payments` `/api/version`) have merged. M5.3 mirrors the same four endpoints on the Python Flask side so M5.4's `cmd/parity` tool can hit both backends and diff the JSON. After M5.3, every byte the Go side emits has a Python counterpart to compare against.
+
+The Python view-model builders ([scripts/views.py](scripts/views.py)) already produce dicts very close to the wire shape — except three template-only fields (`member_data`, `month_labels_json`, `raw_payments_json`) are pre-`json.dumps`'d for inline `<script>` blocks. M5.1's plan called this out explicitly: M5.3's `/api/X` is `jsonify(unwrap_json_strings(view_model_dict))` — a 4-line shim, not real transformation logic.
+
+## Approach
+
+Add four shadow routes to [app.py](app.py) and one private unwrap helper. Builders and templates are untouched.
+
+### Decisions
+
+1. **Unwrap shim lives in `app.py`**, not `scripts/views.py`. It's 4 lines, only the API routes use it, and it's parity-only scaffolding that M8 will delete. Keeping `views.py` free of HTTP-layer concerns means cleaner deletion later.
+2. **No data-loading helper extraction.** Each shadow route duplicates ~8 lines of cache loads from its sibling HTML route. A helper would have to thread `attendance_url` / `payments_url` / `bank_account` and the adults-vs-juniors-vs-payments branching back out — net negative for code that M8 will erase wholesale.
+3. **Drop `record_step` calls in API routes.** `record_step` only feeds `inject_render_time` (a Jinja `context_processor`); JSON responses don't go through templates, so timing breakdown has no consumer.
+4. **`/api/version` is a one-liner.** `BUILD_META` already has the keys (`tag`, `commit`, `build_date`) Go emits. Just `jsonify(BUILD_META)`. Existing `/version` route stays as-is — the new endpoint sits alongside.
+5. **Tests assert key sets and unwrap, not values.** Hard-code `EXPECTED_ADULTS_KEYS` etc. as module constants in [tests/test_app.py](tests/test_app.py). Catches drift in unit tests rather than waiting for M5.4 parity diffs. Type-check the unwrapped fields (`isinstance(member_data, dict)` etc.) to prove the shim ran.
+
+### The shim
+
+```python
+def _unwrap_view_model_for_api(vm: dict) -> dict:
+    out = dict(vm)
+    out["member_data"] = _json.loads(out.pop("member_data"))
+    out["month_labels"] = _json.loads(out.pop("month_labels_json"))
+    out["raw_payments"] = _json.loads(out.pop("raw_payments_json"))
+    return out
+```
+
+Note the **rename**: `month_labels_json` → `month_labels`, `raw_payments_json` → `raw_payments` (matches Go contract per [adults.go](go/internal/web/api/adults.go) JSON tags).
+
+### Route skeleton (`/api/adults`)
+
+```python
+@app.route("/api/adults")
+def api_adults():
+    attendance_url = f"https://docs.google.com/spreadsheets/d/{ATTENDANCE_SHEET_ID}/edit"
+    payments_url = f"https://docs.google.com/spreadsheets/d/{PAYMENTS_SHEET_ID}/edit"
+    members_data = get_cached_data("attendance_regular", ATTENDANCE_SHEET_ID, get_members_with_fees)
+    if not members_data:
+        return jsonify({"error": "no data"}), 503
+    members, sorted_months = members_data
+    transactions = get_cached_data("payments_transactions", PAYMENTS_SHEET_ID, fetch_sheet_data, PAYMENTS_SHEET_ID, CREDENTIALS_PATH)
+    exceptions = get_cached_data(
+        "exceptions_dict", PAYMENTS_SHEET_ID, fetch_exceptions,
+        PAYMENTS_SHEET_ID, CREDENTIALS_PATH,
+        serialize=lambda d: [[list(k), v] for k, v in d.items()],
+        deserialize=lambda c: {tuple(k): v for k, v in c},
+    )
+    result = reconcile(members, sorted_months, transactions, exceptions)
+    vm = build_adults_view_model(
+        members, sorted_months, result, transactions,
+        datetime.now().strftime("%Y-%m"),
+        attendance_url=attendance_url, payments_url=payments_url, bank_account=BANK_ACCOUNT,
+    )
+    return jsonify(_unwrap_view_model_for_api(vm))
+```
+
+`/api/juniors` mirrors with `adapt_junior_members` + `JUNIOR_SHEET_GID` + `build_juniors_view_model`. `/api/payments` skips the unwrap (its builder has no JSON-string fields): `return jsonify(vm)`. `/api/version`: `return jsonify(BUILD_META)`.
+
+## Files to modify
+
+- [app.py](app.py)
+  - L10: add `jsonify` to `from flask import ...`.
+  - Add `_unwrap_view_model_for_api` near [BUILD_META](app.py#L67) (it already imports `json as _json`).
+  - Add four routes: `/api/version`, `/api/adults`, `/api/juniors`, `/api/payments`. Place them after [`/version`](app.py#L143) for grouping.
+- [tests/test_app.py](tests/test_app.py)
+  - Add `EXPECTED_ADULTS_KEYS`, `EXPECTED_JUNIORS_KEYS`, `EXPECTED_PAYMENTS_KEYS`, `EXPECTED_VERSION_KEYS` module constants (sourced from [adults.go](go/internal/web/api/adults.go) / [juniors.go](go/internal/web/api/juniors.go) / [payments.go](go/internal/web/api/payments.go) / [version.go](go/internal/web/api/version.go) JSON tags).
+  - Four new test functions: `test_api_adults`, `test_api_juniors`, `test_api_payments`, `test_api_version`. Reuse the existing `_bypass_cache` patcher and the `fetch_sheet_data` / `fetch_exceptions` / `get_members_with_fees` / `get_junior_members_with_fees` mocks already in the file.
+  - Each adults/juniors test asserts: `200`, `response.is_json`, `set(json.keys()) == EXPECTED_*_KEYS`, `isinstance(json["member_data"], dict)`, `isinstance(json["month_labels"], dict)`, `isinstance(json["raw_payments"], dict)`.
+- [CHANGELOG.md](CHANGELOG.md): post-merge entry per CLAUDE.md format.
+- [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md:102](docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md#L102): tick M5.3 with merge SHA.
+
+## Reusable existing code
+
+- [`build_adults_view_model`](scripts/views.py#L64), [`build_juniors_view_model`](scripts/views.py#L240), [`build_payments_view_model`](scripts/views.py#L432) — call as-is, no changes.
+- [`reconcile`](scripts/match_payments.py) and [`adapt_junior_members`](scripts/views.py#L48) — same.
+- [`get_cached_data`](app.py#L36), [`fetch_sheet_data`](scripts/match_payments.py), [`fetch_exceptions`](scripts/match_payments.py), [`get_members_with_fees`](scripts/attendance.py), [`get_junior_members_with_fees`](scripts/attendance.py) — same call sites as the HTML routes.
+- [`BUILD_META`](app.py#L67) — already shaped to match Go's `VersionResponse`.
+
+## Verification
+
+1. `make test` — all existing tests still pass; four new `test_api_*` tests pass.
+2. `python -c "import app"` — catches the missing `jsonify` import.
+3. `make web-py`, then:
+   - `curl -s localhost:5001/api/version | jq .` → `{tag, commit, build_date}`.
+   - `curl -s localhost:5001/api/adults | jq 'keys'` → 14 keys, no `_json` suffix anywhere.
+   - `curl -s localhost:5001/api/adults | jq '.member_data | type, .month_labels | type, .raw_payments | type'` → all `"object"` (proves unwrap).
+   - Same checks on `/api/juniors` and `/api/payments`.
+4. Visit `/adults`, `/juniors`, `/payments` in browser — HTML still renders identically (regression check on builders).
+5. **Optional pre-M5.4 peek:** `make web-go` on :8080 + `make web-py` on :5001, then `diff <(curl -s :5001/api/adults | jq -S .) <(curl -s :8080/api/adults | jq -S .)`. Expect non-zero diff (raw transaction key shape, see below) — that is fine; M5.4 surfaces and resolves these.
+
+## Out of scope (M5.4 will surface and resolve)
+
+These are known parity friction points; **don't fix in M5.3** — the whole point of M5.4 is to enumerate them:
+
+- **`raw_payments[name][i]` row shape**: Python emits raw Google Sheets row dicts with column-header keys (e.g. `"VS"`, `"Sync ID"`); Go's `RawTransaction` uses snake_case (`vs`, `sync_id`). Keys and types will diverge.
+- **`unmatched[]`**: same divergence (same raw row dicts).
+- **`null` vs missing keys**: Python omits keys never set; Go zero-value structs may emit `null`/`""` depending on `omitempty`.
+- **`Decimal` / float precision** in `grouped_payments` amounts.
+- **Field insertion order**: `jsonify` preserves insertion order (Python 3.7+); Go marshals struct fields in declaration order. Likely fine, parity tool will tell.
+
+## Branch + MR
+
+Per CLAUDE.md: branch `feat/go-m5-3-python-api-shadow`, push with `-u`, open MR via `tea pr create --title ... --description ... --base main --head feat/go-m5-3-python-api-shadow`. Do not merge from CLI.

docs/plans/2026-05-07-2254-m5-4-parity-binary.md

@@ -0,0 +1,152 @@
+# M5.4 — Parity diff binary (`cmd/parity`) + `make parity`
+
+## Context
+
+Per [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md:103](docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md#L103), M5.4 is the next milestone in the Go rewrite. M5.1–M5.3 already landed:
+
+- M5.1: hand-authored Go response structs at [go/internal/web/api/](go/internal/web/api/) + JSON Schemas in [go/tests/fixtures/api-schema/](go/tests/fixtures/api-schema/).
+- M5.2: Go `/api/version|adults|juniors|payments` handlers in [go/internal/web/api/handler.go](go/internal/web/api/handler.go).
+- M5.3: Python shadow endpoints in [app.py:157-224](app.py#L157-L224) using `_unwrap_view_model_for_api` for the same JSON shape.
+
+What's missing: a tool that proves the two backends actually agree on the wire. The M5 gate says "byte-equal JSON between Python and Go for every route." Without a diffing tool, drift between the two implementations slips in silently and we can't gate further milestones (M6 frontend, M7 watch period) on parity.
+
+This task delivers the **parity contract enforcer**: a Go binary that fetches `/api/*` from both backends, scrubs an allowlist of expected diffs, and prints `cmp.Diff` for everything else. Both backends read the same live Google Sheets — that shared state is what makes parity meaningful, no scenario fixtures needed.
+
+## Scope
+
+In scope:
+- New binary `go/cmd/parity/main.go` plus a small support package for the allowlist scrubber.
+- A unit test for the scrubber.
+- New `make parity` target.
+- `go-cmp` promoted to a direct dependency.
+
+Out of scope (explicitly):
+- CI integration / nightly job — that's M7.2.
+- Fixture-driven offline parity — pure-fn parity already runs via `make go-parity` (M3).
+- Hooking `make parity` into `make go-test-all` — leave it manual since it requires two live servers.
+
+## Approach
+
+### 1. New binary: `go/cmd/parity/main.go`
+
+Standalone binary (mirrors task spec — not a subcommand of `fuj`). Stdlib `flag`, no third-party CLI lib.
+
+**Flags:**
+- `-py` — Python base URL, default `http://localhost:5001`
+- `-go` — Go base URL, default `http://localhost:8080`
+- `-route` — optional single route to diff (e.g. `/api/adults`); empty means iterate all four
+- `-timeout` — per-request timeout, default `30s` (sheet fetches are slow on cold cache)
+
+**Routes**, hard-coded:
+```go
+var routes = []string{"/api/version", "/api/adults", "/api/juniors", "/api/payments"}
+```
+All `GET`, no query params (verified in [app.py:157-224](app.py#L157-L224) and [go/internal/web/api/handler.go:27-68](go/internal/web/api/handler.go#L27-L68)).
+
+**Per route, the binary:**
+1. `GET py+route` and `GET go+route` (sequential — keep it simple; total wall time ~1–2s on warm cache).
+2. Verify both return HTTP 200; on non-200, print body and mark route as ERROR.
+3. Decode each body into `map[string]any` (NOT into `api.AdultsResponse` — using the typed struct would silently drop unknown Python-side keys, defeating the diff. Map gives `cmp.Diff` clean dotted-path field names for free.).
+4. Run `scrub(m, allowlist)` on both decoded maps.
+5. `diff := cmp.Diff(pyMap, goMap, cmpopts.EquateEmpty())`.
+6. If `diff != ""`, print `=== /api/X ===` header followed by the diff; track for exit code.
+
+**Exit codes:**
+- `0` — all routes match (or the only diffs were under the allowlist).
+- `1` — at least one route had a non-allowlisted diff.
+- `2` — at least one route failed to fetch / parse (HTTP error, timeout, non-JSON body).
+
+This makes the binary CI-friendly when M7.2 lands.
+
+**Output**: human-readable to stdout — header per route, then "OK" or the diff. Final summary line: `parity: 4/4 routes match` or `parity: 2/4 match, 1 diff, 1 error`.
+
+### 2. Allowlist scrubber
+
+Live in same package (`main`). Keep it tiny — no need for a separate sub-package.
+
+```go
+var defaultAllowlist = []string{"render_time.total", "build_meta"}
+
+// scrub walks m and deletes any key whose dotted path matches an allowlist entry.
+// "render_time.total" deletes m["render_time"]["total"] only (preserves render_time.breakdown).
+// "build_meta" (no dot) deletes m["build_meta"] entirely.
+func scrub(m map[string]any, paths []string) { ... }
+```
+
+Today these fields **don't appear in the JSON** — they're Jinja template-only ([app.py:91-110](app.py#L91-L110)) and the Go side only logs render time via [go/internal/web/middleware/timer.go](go/internal/web/middleware/timer.go). So today the scrub is a no-op. The implementation is forward-compatible insurance: if someone later adds either field to a JSON response on one side only, the parity binary already tolerates it.
+
+The implementation note in [go/internal/web/middleware/timer.go](go/internal/web/middleware/timer.go) ("the elapsed value maps to render_time.total in the M5 JSON allowlist") confirms this is the intended design.
+
+### 3. Unit test
+
+Add `go/cmd/parity/scrub_test.go` with a couple of cases:
+- Scrubbing top-level key (`build_meta`) — key removed; siblings untouched.
+- Scrubbing nested key (`render_time.total`) — only `total` removed; `breakdown` preserved.
+- Path that doesn't exist — no-op, no error.
+- Map without the parent key — no-op (don't panic).
+
+Runs as part of normal `make go-test` (no `-tags` needed).
+
+### 4. Makefile target
+
+Add to [Makefile](Makefile):
+
+```make
+parity:
+	cd $(GO_SRC) && go run ./cmd/parity $(ARGS)
+```
+
+Add `parity` to the `.PHONY` line at [Makefile:1](Makefile#L1) and a `help` entry like:
+
+```
+@echo "  make parity      - Diff /api/* between web-py (:5001) and web-go (:8080); both must be running"
+```
+
+Don't depend on `go-build` — `go run` compiles ad-hoc, and parity is interactive enough that the slight rebuild cost doesn't matter.
+
+### 5. Dependency
+
+`github.com/google/go-cmp v0.7.0` is already a transitive dep ([go/go.sum:24-25](go/go.sum#L24-L25)) but not in `go.mod`'s `require` block. After adding the import, run `go mod tidy` inside `go/` to promote it to direct. No new external deps.
+
+## Files to add / modify
+
+**Add:**
+- [go/cmd/parity/main.go](go/cmd/parity/main.go) — flags, route loop, fetch+scrub+diff, exit codes
+- [go/cmd/parity/scrub_test.go](go/cmd/parity/scrub_test.go) — unit tests for the scrubber
+
+**Modify:**
+- [Makefile](Makefile) — `.PHONY`, help block, `parity` target
+- [go/go.mod](go/go.mod) — promote `go-cmp` to direct (via `go mod tidy`)
+- [go/go.sum](go/go.sum) — likely unchanged (already pinned)
+- [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md) — tick M5.4, add commit SHA
+- [CHANGELOG.md](CHANGELOG.md) — entry per project convention
+
+**Per [CLAUDE.md](CLAUDE.md) plans convention:** copy this plan to `docs/plans/2026-05-07-HHMM-m5-4-parity-binary.md` (timestamp via `date "+%Y-%m-%d-%H%M"`) before opening the MR, since plan files are committed for posterity.
+
+## Existing utilities to reuse
+
+- `cmp.Diff` + `cmpopts.EquateEmpty()` from `github.com/google/go-cmp/cmp` (already in go.sum).
+- Stdlib `net/http`, `encoding/json`, `flag` — sufficient; no need to pull a CLI framework.
+- No existing scrubber to reuse — the one in [scripts/scrub_fixtures.py](scripts/scrub_fixtures.py) operates on the *capture* path and renames PII; the parity scrubber is a different concern (path-based deletion of expected diffs).
+
+## Verification
+
+Manual smoke test (the binary is meant to be run against live servers):
+
+1. **Sanity / build:** `cd go && go build ./cmd/parity && go test ./cmd/parity/...` — compiles + scrubber unit test passes.
+2. **Both backends up:**
+   - Terminal A: `make web-py`
+   - Terminal B: `make web-go`
+   - Terminal C: `make parity`
+   Expected: `parity: 4/4 routes match`, exit 0.
+3. **Negative test:** add a literal extra field to one Go handler temporarily (e.g. `"diagnostic": "test"` in `VersionResponse`), rebuild, re-run `make parity`. Expected: non-zero exit, diff shown for `/api/version`. Revert.
+4. **Allowlist test:** in a unit test (or by manually constructing a payload with `render_time.total` injected), confirm the scrubber removes it before the diff stage.
+5. **CHANGELOG** entry added; progress tracker ticked with the merge commit SHA.
+
+Per [CLAUDE.md](CLAUDE.md) branching policy: this is a feature, so work happens on `feat/go-m5-4-parity-binary`, push with `-u`, open MR with `tea pr create --base main --head feat/go-m5-4-parity-binary`. User merges in Gitea.
+
+## Notes & risks
+
+- **Cache-warmth dependency:** Both backends cache aggressively. A cold-cache fetch on Python can take 30s+ — hence the configurable timeout. If parity is run immediately after `flush-cache`, expect the first run to be slow.
+- **Order-sensitive lists:** `cmp.Diff` on `map[string]any` treats slices as ordered. If either backend ever returns members/transactions in a different order, the diff will flag it — that's a real parity bug, not a false positive, so this is correct behavior. If we hit ordering instability later, fix the source, don't add `cmpopts.SortSlices`.
+- **Float formatting:** Both sides go through `encoding/json` (Go) and `jsonify` (Python `json.dumps`). Floats in totals/balances may format differently (`123` vs `123.0`). If this surfaces, the Go side already uses typed structs with `int` where appropriate — investigate at the source rather than allowlisting.

docs/plans/2026-05-08-0034-go-rewrite-m6-1-template-skeleton.md

@@ -0,0 +1,88 @@
+# Plan: Go rewrite — M6.1 Template skeleton
+
+## Context
+
+M5 finished — Go and Python now produce byte-equal JSON across `/api/{adults,juniors,payments,version}` and `cmd/parity` enforces it. See [progress tracker §M5](2026-05-03-2349-go-backend-rewrite-progress.md#L96-L106).
+
+M6 begins the Go-native HTML frontend that lets us actually retire the Python web UI. **M6.1 is the foundation step**: stand up the base HTML layout, shared nav, terminal-green-on-black theme, and the `embed.FS` plumbing that every subsequent M6 page (adults, juniors, payments, sync, flush, qr) will compose into. After M6.1, opening :8080 shows chrome (header, nav, footer) on every route with placeholder bodies — no real data wiring; that lands in M6.2+.
+
+This is **not a Jinja port**. The Python templates are reference for nav structure and CSS values; the Go layout is designed natively (per the [master plan](2026-05-03-2349-go-backend-rewrite.md#L24-L27): "frontends are allowed to diverge").
+
+## Current Go web state (what we're building on)
+
+- [go/internal/web/server.go](../../go/internal/web/server.go) — `Run()` registers `GET /{$}` (text-plain hello) + four `/api/*` routes. `BuildInfo{Version,Commit,BuildDate}` already flows in.
+- [go/internal/web/api/handler.go](../../go/internal/web/api/handler.go) — central handler struct holding `Sources`, `Config`, `Logger`, build fields.
+- No `templates/`, no `static/`, no `embed` directives, no `html/template` import anywhere in `go/`. We're starting from a blank slate.
+
+## Approach
+
+1. **Create `templates/` and `static/` under `go/internal/web/`**, embedded via `//go:embed`.
+2. **Single base template** (`base.tmpl`) using `html/template` `block`s for `title` and `content`. Each page template defines those blocks; the renderer executes via `ExecuteTemplate(w, "base", data)`.
+3. **Nav partial** parameterized by a `pageData.Active` string so each page highlights its own link with `class="active"`. Three tiers preserved (Primary / Archived / Tools) — matches Python UX in [templates/adults.html:491-505](../../templates/adults.html#L491-L505).
+4. **CSS** lifted verbatim from [templates/adults.html:8-487](../../templates/adults.html#L8-L487) into `static/css/app.css`. Page templates `<link>` it from the base layout. M6.2+ reuses the same class names (`.cell-ok`, `.modal-content`, …) without re-extracting.
+5. **HTML handlers** in a new `go/internal/web/html/` package (sibling of `api/`). One `Handler` struct holding `*Renderer` + `BuildInfo` + `Config`. Routes for `/`, `/adults`, `/juniors`, `/payments`, `/sync-bank`, `/flush-cache` registered in `server.go`. Each route renders a placeholder body ("Coming in M6.X") inside the base shell — the goal is to prove the chrome works, not to populate data.
+6. **Replace the existing `helloHandler`**: `GET /{$}` → `http.Redirect` to `/adults` (mirrors Python's meta-refresh in [app.py:112-115](../../app.py#L112-L115)).
+7. **Static file route**: `GET /static/` served from `staticFS` via `http.StripPrefix("/static/", http.FileServerFS(staticFS))`.
+8. **Footer keeps it simple**: `{{.Build.Version}}@{{.Build.Commit}} | built {{.Build.BuildDate}}`. The Python per-request render-time breakdown is deferred — `middleware/timer.go` only logs to slog today; threading a timer into request context can come back in a later milestone if we miss it.
+
+## Files to create / modify
+
+```
+go/internal/web/
+├── assets.go                          NEW — //go:embed templates/* static/*
+├── render.go                          NEW — Renderer wraps parsed *template.Template
+├── server.go                          MODIFY — drop helloHandler; mount HTML routes + /static/
+├── html/
+│   ├── handler.go                     NEW — html.Handler + page methods
+│   └── handler_test.go                NEW — httptest smoke per route
+├── templates/
+│   ├── base.tmpl                      NEW — <html>/<head>/<body>; nav + content + footer blocks
+│   ├── partials/
+│   │   ├── nav.tmpl                   NEW — three-tier nav, active highlighting
+│   │   └── footer.tmpl                NEW — build meta line
+│   ├── adults.tmpl                    NEW — placeholder "Coming in M6.2"
+│   ├── juniors.tmpl                   NEW — placeholder "Coming in M6.3"
+│   ├── payments.tmpl                  NEW — placeholder "Coming in M6.4"
+│   ├── sync.tmpl                      NEW — placeholder "Coming in M6.6"
+│   └── flush_cache.tmpl               NEW — placeholder "Coming in M6.6"
+└── static/
+    └── css/
+        └── app.css                    NEW — verbatim from templates/adults.html:8-487
+```
+
+## Key design notes
+
+- **Parse once at startup**: `NewRenderer(fs embed.FS)` calls `template.ParseFS(fs, "templates/*.tmpl", "templates/partials/*.tmpl")`. Parse failure aborts boot — template syntax errors surface immediately, not at first request.
+- **Per-page cloned templates** to avoid `define "content"` collisions across pages: `Renderer` stores `map[string]*template.Template` keyed by page name; each is `base+partials` clone with that page's `content`/`title` overlaid.
+- **View model** — small `pageData` struct: `Active` (nav key), `Build` (BuildInfo), `Body` (per-page payload, `any` until M6.2 widens it).
+- **Active-link logic** in nav partial: `{{ if eq .Active "adults" }}class="active"{{ end }}` — markup-side, no template funcs needed.
+- **No JS in M6.1.** Member-detail and QR modals + `static/js/*.js` come in M6.5. M6.1 only sets up the embedded-asset machinery.
+- **Nav anchor labels are literal text** (`[Adults]`, `[Juniors]`, etc.) — keep the brackets in the template strings, they're part of the look.
+- **`/qr` is not in the nav** — it's an image endpoint, M6.6 territory.
+
+## Critical files to read
+
+- [go/internal/web/server.go](../../go/internal/web/server.go) — mux registration; `Run()` signature stays unchanged.
+- [go/internal/web/api/handler.go](../../go/internal/web/api/handler.go) — pattern to mirror for `html.Handler` (same field layout, most fields unused in M6.1).
+- [templates/adults.html:8-487](../../templates/adults.html#L8-L487) — CSS source, copy verbatim.
+- [templates/adults.html:491-505](../../templates/adults.html#L491-L505) — nav markup source (three tiers).
+- [docs/plans/2026-05-03-2349-go-backend-rewrite.md:88-101](2026-05-03-2349-go-backend-rewrite.md#L88-L101) — original layout intent for `web/handlers/`, `web/templates/`, `web/static/`.
+
+## Verification
+
+End-to-end smoke from a fresh `make go-build`:
+
+1. `make web-go &` — server boots; no template-parse errors in slog output.
+2. `curl -i localhost:8080/` → `302` to `/adults`.
+3. `curl -s localhost:8080/adults | grep -F 'class="active"'` matches the Adults anchor only.
+4. `curl -sI localhost:8080/static/css/app.css` → `200`, `Content-Type: text/css`.
+5. Browser at `http://localhost:8080/adults`: terminal-green-on-black theme, three-tier nav at top (Adults active), "Coming in M6.2" placeholder, footer `{tag}@{commit} | built {date}`.
+6. Click each nav link in turn (`/juniors`, `/payments`, `/sync-bank`, `/flush-cache`) — same chrome, the clicked link is highlighted, per-page placeholder body shows.
+7. `make go-test` — `web/html/handler_test.go` passes: each route returns 200, `text/html`, `class="active"` only on the matching anchor.
+8. `make go-lint` clean.
+9. `make parity` still green (regression check — M6.1 doesn't touch `/api/*`).
+10. CHANGELOG entry per CLAUDE.md; M6.1 ticked in [progress tracker §M6.1](2026-05-03-2349-go-backend-rewrite-progress.md#L113) with commit SHA.
+
+## Branch & MR
+
+`feat/go-m6-1-template-skeleton` per CLAUDE.md branch-per-feature workflow. Open MR via `tea pr create --base main --head feat/go-m6-1-template-skeleton`. User merges in the Gitea browser UI.

docs/plans/2026-05-08-0052-go-rewrite-m6-2-adults-page.md

@@ -0,0 +1,131 @@
+# Plan: Go rewrite — M6.2 Adults page
+
+## Context
+
+M6.1 landed the template skeleton, embed.FS, and HTML routes ([progress §M6.1](2026-05-03-2349-go-backend-rewrite-progress.md#L113), commit `78e5059`). Every page renders chrome + a "Coming in M6.X" placeholder body. **M6.2 fills in `/adults`** — the most data-rich page and the template that drives the rest of the M6 work (juniors mostly mirrors it).
+
+Acceptance criteria, verbatim from [progress §M6.2](2026-05-03-2349-go-backend-rewrite-progress.md#L114):
+
+> `/adults` page: table, name filter input, month range filter, totals row, credits/debts/unmatched sections, Pay buttons that link to `/qr`
+
+The Go side has done excellent prep: `buildAdultsResponse` in [go/internal/web/api/build_adults.go](../../go/internal/web/api/build_adults.go) already produces the full view model (currently consumed only by `/api/adults`), the wire types in [go/internal/web/api/types.go](../../go/internal/web/api/types.go) match the Python view-model 1:1, and the CSS is already lifted into [go/internal/web/static/css/app.css](../../go/internal/web/static/css/app.css). M6.2 is therefore mostly **template authoring + handler wiring + a small filters script**, not a fresh port.
+
+## Current Go web state (what we're building on)
+
+- [go/internal/web/server.go:49](../../go/internal/web/server.go#L49) — `mux.HandleFunc("GET /adults", hh.ServeAdults)` already wired.
+- [go/internal/web/html_handler.go:16-18](../../go/internal/web/html_handler.go#L16-L18) — placeholder handler renders a `PageData{Active, Build}` shell only. Needs to gain access to the data layer.
+- [go/internal/web/render.go:11](../../go/internal/web/render.go#L11) — `PageData` struct is currently `{Active, Build}` only. Needs to extend or be wrapped by a typed adults view model.
+- [go/internal/web/api/handler.go:36-45](../../go/internal/web/api/handler.go#L36-L45) — `ServeAdults` already does `loadAll` → `Reconcile` → `buildAdultsResponse`. We will extract that body into an exported method so the HTML handler can reuse it without duplication.
+- [go/internal/web/api/build_adults.go:17](../../go/internal/web/api/build_adults.go#L17) — `buildAdultsResponse(...) AdultsResponse` returns everything the template needs (`Months`, `Results`, `Totals`, `Credits`, `Debts`, `Unmatched`, `BankAccount`, `CurrentMonth`, …). We pass this struct straight into the template.
+- [go/internal/web/templates/adults.tmpl](../../go/internal/web/templates/adults.tmpl) — currently a 5-line placeholder. Replace contents.
+- [go/internal/web/static/css/app.css](../../go/internal/web/static/css/app.css) — all selectors needed (`.cell-ok`, `.cell-unpaid`, `.cell-unpaid-current`, `.cell-overridden`, `.unmatched-row`, `.filter-container`, `.pay-btn`, `.member-row`, …) already present from M6.1.
+
+Reference for parity: [templates/adults.html](../../templates/adults.html) (Python source). Sections to mirror in markup terms:
+- Reconcile table — [adults.html:534-585](../../templates/adults.html#L534-L585)
+- Totals row — [adults.html:571-582](../../templates/adults.html#L571-L582)
+- Credits / Debts — [adults.html:587-609](../../templates/adults.html#L587-L609)
+- Unmatched — [adults.html:611-629](../../templates/adults.html#L611-L629)
+- Filter controls — [adults.html:515-532](../../templates/adults.html#L515-L532)
+- Filter JS (name + month range) — [adults.html:1019-1051](../../templates/adults.html#L1019-L1051)
+
+The member-detail modal, Pay-preview modal, and JSON-hydrated `memberData`/`rawPaymentsByPerson` globals are explicitly **out of scope for M6.2** — they belong to M6.5 (modal JS).
+
+## Approach
+
+1. **Share data assembly between HTML and JSON** — extract `ServeAdults`'s body into `(*api.Handler).AssembleAdults(ctx) (AdultsResponse, error)` and have `ServeAdults` call it. The HTML handler then calls the same method, keeping `/adults` and `/api/adults` byte-identical in semantics (same loaded data, same reconcile, same view model).
+2. **Wire HTMLHandler to data** — extend `HTMLHandler` with an `apiHandler *api.Handler` field and pass it from `Run()`. `ServeAdults` becomes: `AssembleAdults` → on error render an error body (or 500) → render `adults.tmpl` with a typed view model wrapping `PageData` + `api.AdultsResponse`.
+3. **Per-page typed view model** — add `AdultsPageData{ PageData; Data api.AdultsResponse }` in [render.go](../../go/internal/web/render.go) (or a new `view.go`). Template references `.Active`, `.Build` (chrome) and `.Data.Results`, `.Data.Totals`, `.Data.Months`, etc. Keeps the chrome contract for nav/footer untouched.
+4. **Author `adults.tmpl`** — port markup from [templates/adults.html:489-629](../../templates/adults.html#L489-L629). Notable mechanics:
+   - Filter controls block with `<input id="nameFilter">`, `<select id="fromMonth">`, `<select id="toMonth">`, `Apply` / `All` buttons. Month dropdown options rendered server-side from `.Data.Months` (no client-side hydration needed for filters).
+   - Reconcile table iterates `.Data.Results`; each row's months iterate `row.Months`. Cell `<td>` gets class `cell-{{.Status}}`, plus `cell-unpaid-current` when `.RawMonth >= .Data.CurrentMonth`, plus `cell-overridden` when `.Overridden`. Cells carry `data-month-idx="{{$i}}"` so the filter script can hide columns.
+   - Per-cell Pay button visible on hover when `(unpaid|partial)` and `RawMonth < CurrentMonth` — `<a class="pay-btn" href="/qr?...">Pay</a>` with the QR query string built server-side via a template helper (see Key design notes).
+   - Per-row "Pay All" button when `.PayableAmount > 0`, same href construction using `.UnpaidPeriods` for display and `.RawUnpaidPeriods` for the QR message.
+   - Totals `<tr>` iterates `.Data.Totals`, classes `total-cell-{{.Status}}`.
+   - Credits / Debts / Unmatched sections rendered conditionally on non-empty slices.
+5. **Tiny filter script** — new [go/internal/web/static/js/filters.js](../../go/internal/web/static/js/filters.js):
+   - `nameFilter` `input` event: NFD-normalize + lowercase + substring match against `.member-row [data-name]` (or row's first cell text); toggle `display:none` on non-matches.
+   - `fromMonth` / `toMonth` `change` event + `Apply` button: read selected `data-month-idx` range, toggle `month-hidden` class on `[data-month-idx]` `<th>`/`<td>` outside the range.
+   - `All` button: clear filters, restore all rows/cells.
+   - Match Python's behaviour byte-for-byte from [adults.html:864-1051](../../templates/adults.html#L864-L1051) but trimmed of modal/`memberData` calls.
+   - Loaded via `<script src="/static/js/filters.js" defer></script>` from the adults template (or base, if juniors will reuse it — yes, it should be in base or a content-block include).
+6. **`<a href="/qr?…">` Pay buttons now, modal in M6.5** — the M6.6 milestone adds `/qr`. Until then, hrefs return 404. M6.5 will layer modal preview behaviour on top by wrapping clicks; the markup stays the same. This is the simplest staged rollout.
+7. **Template helper for QR href** — add a `funcMap` to `Renderer` with `qrHref(account, amount, name, month string) string` (and a periods-list variant) that builds `/qr?account=…&amount=…&message=…` with proper URL encoding. Implementation: `net/url.Values{}.Encode()`. This keeps URL-construction logic out of the template syntax (`html/template` URL escaping isn't enough — query-param building deserves a Go helper).
+8. **Active-link key** — `Active: "adults"` already set; nav highlighting works as-is (verified in M6.1 smoke test).
+
+## Files to create / modify
+
+```
+go/internal/web/
+├── api/
+│   └── handler.go                MODIFY — extract ServeAdults body to AssembleAdults(ctx)
+├── html_handler.go               MODIFY — hold *api.Handler; ServeAdults loads + renders
+├── render.go                     MODIFY — add AdultsPageData type; add funcMap with qrHref()
+├── server.go                     MODIFY — pass *api.Handler into NewHTMLHandler
+├── html_handler_test.go          MODIFY — add adults markup-level assertions w/ stub Sources
+├── templates/
+│   └── adults.tmpl               MODIFY — replace placeholder w/ full table + filters + sections
+└── static/
+    └── js/
+        └── filters.js            NEW — name + month-range client-side filtering
+```
+
+No new packages; no domain or wire-type changes.
+
+## Key design notes
+
+- **Reuse `buildAdultsResponse` verbatim** — no parallel "view model" needed. `AdultsResponse` already has every field the template wants. `/adults` and `/api/adults` consume the same struct.
+- **Extracting `AssembleAdults`** preserves the parity contract: anything that changes the JSON also changes the HTML, by construction. (It also sets up the same pattern for M6.3 juniors and M6.4 payments.)
+- **Filter UX is DOM-driven**, no JSON hydration. `member_data` / `raw_payments` JSON payloads stay deferred to M6.5 (modal needs them; filters do not).
+- **`current_month` boundary is server-side** — `AdultsResponse.CurrentMonth` (set from `time.Now().Format("2006-01")` in `loadAll`) is what the template compares `RawMonth` against for `cell-unpaid-current` styling and Pay-button visibility. Same value Python passes through `vm["current_month"]`.
+- **`html/template` autoescaping is sufficient** for member names, sender, message, etc. — but Pay-button URLs need explicit `url.Values` encoding (Czech names have diacritics and spaces). Hence the `qrHref` funcMap helper.
+- **Error rendering**: if `AssembleAdults` fails, render the base shell with an error banner inside `content` rather than `http.Error`. Keeps nav visible so the user can navigate away. Match Python's `"No data."` fallback at [app.py:233](../../app.py#L233) for empty results.
+- **No JS framework, no bundler** — filter script is plain ES2020, ~80 lines, inline-readable. Matches M6.1's "no JS in M6.1" follow-through (we add JS in M6.2, but kept minimal).
+- **NFD-normalize** in JS via `s.normalize('NFD').replace(/\p{Diacritic}/gu, '').toLowerCase()` to match Python's `unicodedata.normalize('NFD', ...)`. Python ref: [adults.html:868-873](../../templates/adults.html#L868-L873).
+- **Filter persistence is out of scope** — Python's filters are session-only (no localStorage). Same here.
+
+## Critical files to read
+
+- [go/internal/web/api/build_adults.go](../../go/internal/web/api/build_adults.go) — full view model already built; the template just iterates over `AdultsResponse`.
+- [go/internal/web/api/types.go:91-122](../../go/internal/web/api/types.go#L91-L122) — `MonthCell`, `TotalCell`, `MemberRow`, `Credit` shapes.
+- [go/internal/web/api/handler.go:36-96](../../go/internal/web/api/handler.go#L36-L96) — pattern for `loadAll` + `Reconcile` + `buildAdultsResponse`; the bit to refactor into `AssembleAdults`.
+- [go/internal/web/static/css/app.css](../../go/internal/web/static/css/app.css) — class names available; no edits needed.
+- [templates/adults.html:489-629](../../templates/adults.html#L489-L629) — markup reference for filter controls, table, totals, credits/debts, unmatched.
+- [templates/adults.html:864-1051](../../templates/adults.html#L864-L1051) — JS reference for filter behaviour (NFD-normalize, month range hiding, Apply/All).
+- [tests/test_app.py:50-75](../../tests/test_app.py#L50-L75) — `test_adults_route` in Python, mirror its assertions in Go: status 200, body contains member name + `750/750 CZK (4)` + `Adults Dashboard`, does not contain `OK`.
+
+## Verification
+
+End-to-end smoke after `make go-build`:
+
+1. `make web-go &` — server boots, no template-parse errors.
+2. `curl -i localhost:8080/adults` → `200`, `Content-Type: text/html`.
+3. Browser at `http://localhost:8080/adults` against real data:
+   - Table renders with one row per adult member, one column per month, totals row at bottom.
+   - Cell colors match `/api/adults` JSON — pick a `Credits` member from JSON, confirm green-ish status; pick a `Debts` member, confirm red-ish.
+   - Credits / Debts / Unmatched sections render with content matching the JSON arrays for those keys.
+   - Per-cell `Pay` buttons appear on hover for past-month unpaid/partial cells; href contains `/qr?account=...&amount=...&message=`.
+   - Per-row "Pay All" button shows for members with `payable_amount > 0`.
+4. Filters:
+   - Type a partial member name in `#nameFilter` → only matching rows visible. Test with diacritics (e.g. `nemec` matches `Němec`).
+   - Pick `fromMonth=2026-02`, `toMonth=2026-04`, click `Apply` → only those columns visible (table + totals row).
+   - Click `All` → everything restored.
+5. `curl -s localhost:8080/adults | grep -F 'Adults Dashboard'` matches; `grep -F 'Coming in M6.2'` does **not** match.
+6. `make go-test` — `html_handler_test.go` adults assertions pass with stub Sources fixture (replicating `test_adults_route` from Python).
+7. `make go-lint` clean.
+8. `make parity` still green — `/api/adults` JSON unchanged because `AssembleAdults` extraction is a pure refactor.
+9. CHANGELOG entry per CLAUDE.md (timestamp via `date "+%Y-%m-%d %H:%M %Z"`).
+10. Tick M6.2 in [progress tracker §M6.2](2026-05-03-2349-go-backend-rewrite-progress.md#L114) with the merge commit SHA.
+
+## Branch & MR
+
+Branch `feat/go-m6-2-adults-page` per CLAUDE.md branch-per-feature workflow. Commit, push with `-u`, then:
+
+```bash
+tea pr create \
+  --title "feat(go): M6.2 — adults page (table, filters, credits/debts/unmatched, Pay buttons)" \
+  --description "..." \
+  --base main \
+  --head feat/go-m6-2-adults-page
+```
+
+Print the PR URL for the user. User merges in Gitea browser.

docs/plans/2026-05-08-1052-period-selector-missing-old-months.md

@@ -0,0 +1,142 @@
+# Period selector missing older months — diagnosis
+
+## Context
+
+User reports the "From / To" period selector on the **adults** dashboard now
+shows **Dec 2025** as the oldest available period. The older production
+deployment shows Sep+Oct 2025, Nov 2025, Dec 2025+Jan 2026 (merged labels) —
+i.e. data going back to September 2025. The user wants to know what went
+sideways. Confirmed: the dropdown options on both Python and Go genuinely
+start at Dec 2025, not just the default selection — Sep/Oct/Nov 2025 are not
+in the list at all.
+
+## Root cause — the live adults sheet header is missing those columns
+
+The fresh cache files at `tmp/go/attendance_regular_cache.json` (raw rows from
+Google Sheets, modifiedTime `2026-05-06T22:30:02Z`, cached `2026-05-08T00:26`)
+contain the actual header row for the adults tab (gid=0):
+
+```text
+['FUJ tréninky úterý 20:30-22:00', '', '', '02.12.2025', '09.12.2025',
+ '16.12.2025', '06.01.2026', '13.01.2026', '20.01.2026', '27.01.2026',
+ '03.02.2026', '10.02.2026', '17.02.2026', '24.02.2026', '03.03.2026',
+ '10.03.2026', '17.03.2026', '23.03.2026', '31.03.2026', '13.04.2026',
+ '20.04.2026', '27.04.2026', '04.05.2026', '', '', '']
+```
+
+**The first date column in the live adults sheet is `02.12.2025` (Dec 2 2025).**
+There are no September, October, or November 2025 columns in the header at
+all. Both backends parse this faithfully (no slicing, no cutoff anywhere) and
+correctly produce `sortedMonths = ["2025-12", "2026-01", …, "2026-05"]`.
+
+The juniors sheet (different tab, `JUNIOR_SHEET_GID`) is **fine** — its header
+still contains `['', 'tier', '', '15.09.2025', '13.10.2025', '20.10.2025',
+'03.11.2025', '24.11.2025', '10.11.2025', '17.11.2025', '01.12.2025', …]`. So
+the juniors page still shows Sep+Oct / Nov / Dec+Jan correctly.
+
+So this is a **data issue in the adults attendance Google Sheet**: at some
+point between when production's cache was last warmed (showing Sep–Nov) and
+2026-05-06, somebody (or some action) removed the columns for September,
+October, and November 2025 from the adults tab header.
+
+The code is doing exactly what it should. There is no parser regression.
+
+## What to do
+
+### 1. Restore the missing date columns in the adults attendance sheet
+
+The fix lives in Google Sheets, not in the codebase. Options, in order of
+preference:
+
+- **(a) Use Sheets version history.** File → Version history → See version
+  history; find a version from before the columns were dropped (anything
+  before about Mar 2026 should still have them). Copy the Sep/Oct/Nov 2025
+  date column headers and the `TRUE/FALSE` cells underneath them back into
+  the current sheet. Only restore the 11 missing date columns; do not
+  full-revert (you'd lose every change since then).
+- **(b) Pull from the production server's cache.** The production deployment
+  evidently still has the older cache, since its dashboard renders those
+  months. SSH there, copy `tmp/attendance_regular_cache.json`, and you can
+  reconstruct the per-member Sep/Oct/Nov attendance counts from the
+  `data[*][2]` map (keys `"2025-09"`, `"2025-10"`, `"2025-11"`). Re-enter
+  those into the sheet manually as date columns + `TRUE` cells — tedious but
+  deterministic.
+- **(c) Accept the loss.** If the older columns aren't recoverable, the
+  dashboard correctly reflects what the sheet contains; nothing more to do.
+
+Which to pick depends on whether those months still need to be billed /
+reconciled.
+
+### 2. Restore `ADULT_MERGED_MONTHS` (user confirmed this was unintentional)
+
+Independent of the sheet issue: commit `1257f0d` (Mar 9 2026) commented out
+the adult merge mappings. Once the Sep/Oct/Nov columns are back in the sheet,
+the dashboard would still show them as separate periods instead of the
+production-style "Sep+Oct 2025" and "Dec 2025+Jan 2026" merged labels.
+
+User confirmed this was unintentional. Two files to update:
+
+- [scripts/attendance.py:32-35](scripts/attendance.py#L32-L35) — uncomment
+  the two mappings:
+
+  ```python
+  ADULT_MERGED_MONTHS = {
+      "2025-12": "2026-01",   # keys are merged into values
+      "2025-09": "2025-10",
+  }
+  ```
+
+- [go/internal/services/membership/sources.go:30](go/internal/services/membership/sources.go#L30) — mirror the same:
+
+  ```go
+  var AdultMergedMonths = map[string]string{
+      "2025-12": "2026-01",
+      "2025-09": "2025-10",
+  }
+  ```
+
+After this change, hit `POST /flush-cache` on each backend so the in-process
+post-processed adults cache is rebuilt with the new mapping.
+
+### 3. (Optional, separate) Fix the JS auto-default that hides older months
+
+This is **not** the cause of the user's current symptom (that's the sheet
+issue), but it will become a UX issue once Sep/Oct/Nov columns are restored:
+the Python frontend's `defaultFrom = Math.max(0, maxMonthIdx - 4)` will still
+default the From-selector to ~5 months before the latest column on every page
+load, hiding restored older months until the user manually picks them.
+
+- [templates/adults.html:1047](templates/adults.html#L1047) — `var defaultFrom = Math.max(0, maxMonthIdx - 4);`
+- [templates/juniors.html:1028](templates/juniors.html#L1028) — same line.
+
+Drop those four lines (`defaultFrom`, `fromSelect.value = defaultFrom`,
+`toSelect.value = maxMonthIdx`, `applyMonthFilter()`) so the page loads with
+all non-future months visible — matching the Go side, which only calls
+`hideFutureMonths()` and leaves From at its first option.
+
+Recommend bundling this with step 2 since they touch related UI.
+
+## Verification
+
+1. **After step 1** — `POST /flush-cache` on Python and Go backends; reload
+   `/adults` on each. Confirm the dropdown now lists Sep/Oct/Nov 2025.
+2. **After step 2** — reload `/adults`. Confirm the dropdown shows
+   "Sep+Oct 2025" as a single period and "Dec 2025+Jan 2026" as a single
+   period. (Still requires the sheet columns to exist.)
+3. **After step 3** — reload `/adults` and `/juniors` on Python. Confirm the
+   table renders all non-future months on first load (Sep 2025 through the
+   current month) instead of starting at Dec 2025.
+4. **Parity check** — `make parity` should report zero diffs between Python
+   and Go on `/api/adults` and `/api/juniors`.
+
+## Critical files referenced
+
+- `tmp/go/attendance_regular_cache.json` — current adults sheet rows
+  (evidence: header starts at `02.12.2025`).
+- `tmp/go/attendance_juniors_cache.json` — current juniors sheet rows
+  (header still has `15.09.2025`).
+- [scripts/attendance.py](scripts/attendance.py) — `ADULT_MERGED_MONTHS`
+  empty after `1257f0d`; `parse_dates` / `group_by_month` faithful.
+- [go/internal/services/membership/sources.go](go/internal/services/membership/sources.go) — Go counterpart, same shape.
+- [templates/adults.html](templates/adults.html), [templates/juniors.html](templates/juniors.html) — JS onload `defaultFrom = -4` issue (step 3).
+- [go/internal/web/static/js/filters.js](go/internal/web/static/js/filters.js) — Go filter UI (already correct, no changes).

docs/plans/2026-05-08-1123-go-m6-3-juniors-page.md

@@ -0,0 +1,67 @@
+# M6.3 — Go-native `/juniors` page
+
+## Context
+
+The Go rewrite is in milestone M6 (Go-native HTML frontend). M6.2 shipped the `/adults` page in commit `c85748b`; the [progress tracker](../../srv/personal/fuj-management/docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md) line 115 names M6.3 as:
+
+> `/juniors` page: same structure + per-month J/A attendance breakdown + `"?"` sentinel rendering
+
+The Go side already has `buildJuniorsResponse` (M5.2) that produces the full JSON view model, and the JuniorsResponse uses the same `MemberRow`/`MonthCell`/`TotalCell` types as `AdultsResponse`. Critically, `buildJuniorMemberRow` ([go/internal/web/api/build_juniors.go:142](../../srv/personal/fuj-management/go/internal/web/api/build_juniors.go#L142)) already bakes the J/A breakdown (e.g. `"3/500 CZK (4:2J,2A)"`) and the `"?"` sentinel into `MonthCell.Text` — no template-level junior-specific logic is required for the M6.3 table.
+
+Today `juniors.tmpl` is a 4-line "Coming in M6.3" placeholder and `HTMLHandler.ServeJuniors` ([html_handler.go:35](../../srv/personal/fuj-management/go/internal/web/html_handler.go#L35)) just renders that placeholder. Goal of M6.3: produce a working `/juniors` page that mirrors the structure of `/adults` and reaches feature parity with the Python `/juniors` route.
+
+## Approach
+
+Mirror the M6.2 pattern exactly:
+
+1. **Extract `AssembleJuniors(ctx)`** from the JSON handler so HTML + JSON share one view-model assembly path (the parity contract).
+2. **Add `JuniorsPageData`** wrapper type next to `AdultsPageData` in `render.go`.
+3. **Replace `juniors.tmpl`** with an adults-shaped layout. Because `JuniorsResponse` shares the same field names used by `adults.tmpl` (`Months`, `RawMonths`, `Results`, `Totals`, `Credits`, `Debts`, `AttendanceURL`, `PaymentsURL`, `BankAccount`, `CurrentMonth`), the template body is essentially copy/paste with one parity tweak (see "Decisions" below).
+4. **Wire `HTMLHandler.ServeJuniors`** to call `AssembleJuniors` and render the new template, parallel to `ServeAdults`.
+
+No new CSS, no new JS — `filters.js` and the `cell-*` classes (lifted in M6.1) already cover juniors.
+
+## Files to modify
+
+| File | Change |
+| --- | --- |
+| [go/internal/web/api/handler.go](../../srv/personal/fuj-management/go/internal/web/api/handler.go) | Add `AssembleJuniors(ctx) (JuniorsResponse, error)`; refactor existing `ServeJuniors` to call it (mirrors `AssembleAdults` at line 47). |
+| [go/internal/web/render.go](../../srv/personal/fuj-management/go/internal/web/render.go) | Add `JuniorsPageData` struct (PageData + `Data api.JuniorsResponse` + `Error string`). |
+| [go/internal/web/html_handler.go](../../srv/personal/fuj-management/go/internal/web/html_handler.go) | Replace stub `ServeJuniors` with the same shape as `ServeAdults` (lines 20–33). |
+| [go/internal/web/templates/juniors.tmpl](../../srv/personal/fuj-management/go/internal/web/templates/juniors.tmpl) | Replace placeholder with a structurally identical copy of [adults.tmpl](../../srv/personal/fuj-management/go/internal/web/templates/adults.tmpl), with the title swapped to "Juniors Dashboard" and the Unmatched section removed (parity with Python). |
+| [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](../../srv/personal/fuj-management/docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md) | Tick `M6.3` once merged, append merge SHA. |
+| [CHANGELOG.md](../../srv/personal/fuj-management/CHANGELOG.md) | New top-most entry per CLAUDE.md format. |
+
+## Decisions captured
+
+- **No "Unmatched Transactions" section on `/juniors`.** Python's [templates/juniors.html](../../srv/personal/fuj-management/templates/juniors.html) renders only Credits + Debts (no Unmatched block). Although `JuniorsResponse.Unmatched` is populated, parity says we don't render it on juniors. The data stays available for the modal in M6.5.
+- **Reuse `qrHref` / `qrHrefAll` template funcs** from [render.go:35–57](../../srv/personal/fuj-management/go/internal/web/render.go#L35-L57). They are name-only (not adult-specific) and already on `tmplFuncs`.
+- **Reuse the existing `cell-empty / cell-unpaid / cell-unpaid-current / cell-ok / cell-overridden` cell-class branching** from `adults.tmpl` lines 60–67 verbatim. The "?" sentinel is rendered as plain `{{$cell.Text}}` text — no template branch needed because `buildJuniorMemberRow` produces `"?"` or `"? CZK"` already.
+- **No template helper extraction** (e.g. shared `_table_section.tmpl`). The two templates will be near-duplicates, but extracting a shared partial now is premature — wait until M6.4 or later when patterns settle. M6.2 didn't extract one either.
+- **Branch**: `feat/go-m6-3-juniors-page`, MR via `tea pr create` per CLAUDE.md.
+
+## Verification
+
+End-to-end smoke (parallel-running both backends as in M5/M6.2):
+
+1. `cd go && make run` (or whatever target boots the Go server on :8080).
+2. Browser-load `http://localhost:8080/juniors`. Confirm:
+   - Member rows render with cells containing fee + attendance breakdown like `0/500 CZK (3:2J,1A)`.
+   - At least one `"?"` cell visible (any junior with exactly one session in some month).
+   - Filter input narrows rows by name; From/To month selects hide columns via `data-month-idx`.
+   - `Pay` button visible on past-month unpaid cells; clicking links to `/qr?...`. (The QR endpoint itself lands in M6.6 — only the link target is in scope here.)
+   - `Pay All` visible on rows with `Balance < 0`.
+   - TOTAL row sums correctly per month.
+   - Credits + Debts sections render when present; no Unmatched section.
+3. JSON parity: `make parity` against the M3 fixture corpus must still report zero non-allowlisted diffs for `/api/juniors` (the `AssembleJuniors` extraction must not change wire output).
+4. Compare side-by-side against Python `/juniors` on :5001 for the same fixture; the table cells should match cell-for-cell modulo the known M5 allowlist.
+
+## Out of scope
+
+- Modal (`[i]` info button + `#memberModal`) — that is M6.5.
+- QR endpoint, `/sync-bank`, `/flush-cache`, `/version` pages — M6.6.
+- Embed.FS deploy verification — M6.7.
+
+## Plan-file relocation
+
+Per [CLAUDE.md](../../srv/personal/fuj-management/CLAUDE.md) "Plans" section, plan files belong in `docs/plans/YYYY-MM-DD-HHMM-<slug>.md` inside the repo. Plan mode forced this draft into `~/.claude/plans/`; first step after ExitPlanMode is to copy this file to `docs/plans/2026-05-08-HHMM-go-m6-3-juniors-page.md` (resolving the timestamp at that moment) and commit it on the feature branch alongside the implementation.

docs/plans/2026-05-08-1220-go-m6-4-payments-page.md

@@ -0,0 +1,215 @@
+# M6.4 — Go-native `/payments` page (grouped-by-person ledger)
+
+> Plan-mode note: per project convention this plan should live at
+> `docs/plans/2026-05-08-1220-go-m6-4-payments-page.md`. The first execution
+> step after approval is to copy this file there.
+
+## Context
+
+The Go port of the Flask app is at milestone **M6.4**: replace the placeholder
+`/payments` template ([go/internal/web/templates/payments.tmpl](go/internal/web/templates/payments.tmpl))
+with a feature-equivalent grouped-by-person ledger view, matching the Python
+[templates/payments.html](templates/payments.html) page.
+
+Compared to M6.2 (`/adults`) and M6.3 (`/juniors`), this page is **structurally
+much simpler**:
+
+- No filters (no name input, no month-range selects).
+- No totals / credits / debts / unmatched-as-extra-section.
+- No JS (no `filters.js`, no modal — modal is M6.5 territory and Python's
+  payments page itself has none).
+- No QR / Pay buttons.
+- Single grouping dimension: **by person**, sorted alphabetically, with a
+  synthetic `"Unmatched / Unknown"` bucket appended.
+- Each person's transactions sorted **newest-first**.
+- Columns: Date, Amount (right-aligned, green), Purpose, Bank Message.
+
+The JSON API side is already done (`/api/payments` at
+[go/internal/web/api/handler.go:78-86](go/internal/web/api/handler.go#L78-L86)),
+returning a `PaymentsResponse{ GroupedPayments, SortedPeople, AttendanceURL,
+PaymentsURL }`. The HTML side just needs to consume it.
+
+## Approach
+
+Mirror the M6.2/M6.3 pattern: extract an `AssembleX(ctx)` method, add a typed
+`PageData` wrapper, render a real template, lift the page-specific CSS into the
+shared stylesheet.
+
+### 1. Extract `AssemblePayments(ctx) (PaymentsResponse, error)`
+
+In [go/internal/web/api/handler.go](go/internal/web/api/handler.go), refactor
+`ServePayments` (currently inlines the load+build at lines 78-86) to mirror
+`AssembleAdults` / `AssembleJuniors`:
+
+```go
+func (h *Handler) ServePayments(w http.ResponseWriter, r *http.Request) {
+    resp, err := h.AssemblePayments(r.Context())
+    if err != nil { h.writeError(w, r, err); return }
+    writeJSON(w, resp)
+}
+
+func (h *Handler) AssemblePayments(ctx context.Context) (PaymentsResponse, error) {
+    txns, err := h.Sources.LoadTransactions(ctx)
+    if err != nil { return PaymentsResponse{}, fmt.Errorf("load transactions: %w", err) }
+    return buildPaymentsResponse(txns, h.allMemberNames(ctx)), nil
+}
+```
+
+Pure refactor — `make parity` should report zero diffs on `/api/payments`.
+
+### 2. Add `PaymentsPageData` wrapper
+
+In [go/internal/web/render.go](go/internal/web/render.go), alongside
+`AdultsPageData` / `JuniorsPageData`:
+
+```go
+type PaymentsPageData struct {
+    PageData
+    Data  api.PaymentsResponse
+    Error string
+}
+```
+
+No changes needed to `pageNames` — `"payments"` is already registered.
+
+### 3. Rewire HTML handler
+
+Replace [go/internal/web/html_handler.go:50-52](go/internal/web/html_handler.go#L50-L52):
+
+```go
+func (h *HTMLHandler) ServePayments(w http.ResponseWriter, r *http.Request) {
+    data := PaymentsPageData{ PageData: PageData{Active: "payments", Build: h.build} }
+    resp, err := h.apiHandler.AssemblePayments(r.Context())
+    if err != nil { data.Error = err.Error() } else { data.Data = resp }
+    h.renderer.Render(w, "payments", data)
+}
+```
+
+### 4. Replace template stub
+
+Rewrite [go/internal/web/templates/payments.tmpl](go/internal/web/templates/payments.tmpl)
+(currently a 5-line placeholder). Structure:
+
+```gotmpl
+{{define "title"}}Payments Ledger{{end}}
+{{define "content"}}
+<h1>Payments Ledger</h1>
+<p class="description">
+  All bank transactions from the
+  <a href="{{.Data.PaymentsURL}}" target="_blank">payments sheet</a>,
+  grouped by member. Names are matched against the
+  <a href="{{.Data.AttendanceURL}}" target="_blank">attendance sheet</a>.
+</p>
+{{if .Error}}<p class="error">{{.Error}}</p>{{end}}
+<div class="ledger-container">
+{{range $person := .Data.SortedPeople}}
+  <div class="member-block">
+    <h2>{{$person}}</h2>
+    <table class="txn-table">
+      <thead><tr>
+        <th class="txn-date">Date</th>
+        <th class="txn-amount">Amount</th>
+        <th class="txn-purpose">Purpose</th>
+        <th class="txn-message">Bank Message</th>
+      </tr></thead>
+      <tbody>
+      {{range $tx := index $.Data.GroupedPayments $person}}
+        <tr>
+          <td class="txn-date">{{$tx.Date}}</td>
+          <td class="txn-amount">{{printf "%.0f" $tx.Amount}} CZK</td>
+          <td class="txn-purpose">{{$tx.Purpose}}</td>
+          <td class="txn-message">{{$tx.Message}}</td>
+        </tr>
+      {{end}}
+      </tbody>
+    </table>
+  </div>
+{{end}}
+</div>
+{{end}}
+```
+
+Notes:
+- `printf "%.0f"` matches the visual style of integer CZK amounts (Python prints
+  the float as-is, but bank-row amounts are always whole CZK). If the user
+  prefers exact Python parity (`750.0 CZK`), drop the `printf` and use
+  `{{$tx.Amount}}`.
+- Iterating a `map` requires using `.Data.SortedPeople` to drive order then
+  `index $.Data.GroupedPayments $person` — Go templates don't preserve map
+  insertion order.
+
+### 5. Add CSS classes to `app.css`
+
+Append the page-specific rules from [templates/payments.html:111-164](templates/payments.html#L111-L164)
+to [go/internal/web/static/css/app.css](go/internal/web/static/css/app.css):
+`.ledger-container`, `.member-block`, `.txn-table`, `.txn-table th/td`,
+`.txn-date`, `.txn-amount`, `.txn-purpose`, `.txn-message`, `tr:hover`. The
+terminal-green palette already matches.
+
+### 6. Unit test
+
+Add a markup-level test to `go/internal/web/html_handler_test.go` (the file
+created in M6.2/M6.3) following the same pattern: stub `Sources` returning a
+fixed transaction list, assert response is HTML 200, assert key strings appear
+(person names as `<h2>`, "Payments Ledger" `<h1>`, expected amount, "Unmatched
+/ Unknown" bucket when an unattributed tx exists).
+
+## Critical files
+
+| Action  | Path |
+|---------|------|
+| edit    | [go/internal/web/api/handler.go](go/internal/web/api/handler.go) — extract `AssemblePayments` |
+| edit    | [go/internal/web/render.go](go/internal/web/render.go) — add `PaymentsPageData` |
+| edit    | [go/internal/web/html_handler.go](go/internal/web/html_handler.go) — rewire `ServePayments` |
+| rewrite | [go/internal/web/templates/payments.tmpl](go/internal/web/templates/payments.tmpl) — real template |
+| edit    | [go/internal/web/static/css/app.css](go/internal/web/static/css/app.css) — append ledger CSS |
+| edit    | `go/internal/web/html_handler_test.go` — payments markup test |
+
+No changes to `server.go`, `assets.go`, `Sources` interface, `buildPaymentsResponse`,
+or any domain code — these were completed in M5 / M6.1.
+
+## Reused existing helpers
+
+- [go/internal/web/api/build_payments.go](go/internal/web/api/build_payments.go) — `buildPaymentsResponse` (existing, unchanged)
+- [go/internal/web/api/build_common.go:84-117](go/internal/web/api/build_common.go#L84-L117) — `groupRawPaymentsByPerson` handles canonicalization, comma-splitting, `[?]` stripping, newest-first sort
+- [go/internal/web/api/handler.go:116-129](go/internal/web/api/handler.go#L116-L129) — `allMemberNames`
+- [go/internal/web/templates/partials/nav.tmpl](go/internal/web/templates/partials/nav.tmpl) and `footer.tmpl` — already include the `[Payments Ledger]` nav link
+
+## Verification
+
+End-to-end:
+
+1. `cd go && make go-build go-test go-lint` — all green.
+2. `make parity` — confirm the `AssemblePayments` extraction is byte-equal on
+   `/api/payments`.
+3. `make web-go &` then:
+   - `curl -i localhost:8080/payments | head -30` — HTTP 200, `text/html`.
+   - Browser load `http://localhost:8080/payments`:
+     - "Payments Ledger" heading + description with two clickable sheet links.
+     - Alphabetical member blocks, each with a table.
+     - Amounts right-aligned, green, "CZK" suffix.
+     - Newest-first ordering inside each block.
+     - "Unmatched / Unknown" bucket sorts in alphabetical position (capital U →
+       near end).
+     - Hover on a row darkens the background.
+     - Nav highlights `[Payments Ledger]` as the active link.
+   - Cross-check with Python: `make web-py &` → `http://localhost:5001/payments`
+     should look visually identical except for nav styling.
+4. `make web-py & make web-go &` then `tea pr create` once committed (per
+   project branch-per-feature workflow).
+
+## Branching
+
+Create `feat/go-m6-4-payments-page` off `main`, push, open MR via `tea`.
+Follow project conventions: Co-Authored-By trailer, CHANGELOG entry once user
+confirms it works, tick **M6.4** in
+[docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md:116](docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md#L116)
+with the merge SHA after the user merges in Gitea.
+
+## Out of scope (deferred)
+
+- **Modal / `[i]` info button** — M6.5 (not present in Python `/payments` either).
+- **Period selector** — `/payments` has none in Python; not adding one.
+- **embed.FS deploy verification** — M6.7.
+- **Shared partial extraction** — payments structurally diverges from
+  adults/juniors enough that there's no obvious common partial to lift; defer.

docs/plans/2026-05-08-1259-go-m6-5-modal-js.md

@@ -0,0 +1,288 @@
+# M6.5 — Member-detail modal JS module (`/adults`, `/juniors`)
+
+> Plan-mode note: per project convention this plan should live at
+> `docs/plans/2026-05-08-HHMM-go-m6-5-modal-js.md` (use `date "+%Y-%m-%d-%H%M"`
+> when copying). The first execution step after approval is to copy this file
+> there. Branch: `feat/go-m6-5-modal-js` off `main`.
+
+## Context
+
+The Go port of the Flask app is at milestone **M6.5**: the `/adults` and
+`/juniors` pages currently render their tables ([go/internal/web/templates/adults.tmpl](go/internal/web/templates/adults.tmpl),
+[go/internal/web/templates/juniors.tmpl](go/internal/web/templates/juniors.tmpl))
+but have no row-click member-detail modal — the feature that lets a user click
+a member's row to inspect status per month, exception overrides, "other"
+transactions, the matched payment list, and a debug raw-payments view.
+
+The Python implementation lives inline in
+[templates/adults.html:718-993](templates/adults.html#L718-L993)
+(matching code in [templates/juniors.html](templates/juniors.html) — same
+modal markup and JS). It uses globals injected via Jinja:
+`memberData`, `sortedMonths`, `monthLabels`, `rawPaymentsByPerson`. M6.5
+replaces this with a clean static JS module.
+
+Per milestone wording — *"fetches `/api/adults` (or juniors), renders
+status/exceptions/transactions on row click; keyboard nav (Esc, ↑/↓)"* —
+and per the user's design choice: the JS module fetches `/api/<page>` **once
+on page load** and caches the response in a module-scoped variable. Subsequent
+row clicks render synchronously from cache. This keeps HTML purely
+server-rendered and reuses the parity-tested JSON contract already shipped in
+M5.
+
+All the building blocks are already in place:
+
+- **JSON API**: `/api/adults` and `/api/juniors` already return
+  `member_data`, `month_labels`, `raw_payments` as nested objects (see
+  [go/internal/web/api/adults.go:27-42](go/internal/web/api/adults.go#L27-L42)
+  and the analogous juniors response). Junior `Expected` serialises as `"?"`
+  for the unknown sentinel via custom `MarshalJSON`
+  ([go/internal/web/api/types.go:24-29](go/internal/web/api/types.go#L24-L29)) — JS sees a literal string `"?"`.
+- **CSS**: `#memberModal`, `.modal-content`, `.modal-section`, `.modal-table`,
+  `.tx-list`, `.tx-item`, `.tx-meta`, `.tx-amount`, `.info-icon`, `.raw-toggle`
+  were lifted whole during M6.1 and live in
+  [go/internal/web/static/css/app.css](go/internal/web/static/css/app.css)
+  (lines 168-487). No CSS work needed.
+- **Member-row hooks**: `tr.member-row[data-name="..."]` and `td.member-name`
+  are already rendered by both templates.
+- **JS module convention**: `static/js/filters.js` is loaded with `<script src="/static/js/filters.js" defer>`;
+  M6.5 adds a sibling `static/js/member-detail.js` with the same loading
+  pattern.
+
+## Approach
+
+### 1. Add `[i]` info icon + `#memberModal` markup to both templates
+
+In [go/internal/web/templates/adults.tmpl](go/internal/web/templates/adults.tmpl)
+and [go/internal/web/templates/juniors.tmpl](go/internal/web/templates/juniors.tmpl):
+
+a. Inside the `<td class="member-name">{{$row.Name}}</td>` cell (line 59 of
+   each template), append the icon button:
+
+   ```gotmpl
+   <td class="member-name">{{$row.Name}}<span class="info-icon" data-name="{{$row.Name}}" title="Show details">[i]</span></td>
+   ```
+
+   Using a `data-name` attribute and a CSS class (rather than `onclick="..."`)
+   keeps the template free of inline JS — the module wires up the listener
+   itself.
+
+b. After the closing `</div>` of the table-container / sections, before the
+   `<script>` tag at line 140 (adults) / 120 (juniors), inject the modal
+   markup. Mirror the Python structure verbatim
+   ([templates/adults.html:644-707](templates/adults.html#L644-L707)):
+
+   ```gotmpl
+   <div id="memberModal" class="modal" onclick="if (event.target === this) this.classList.remove('active')">
+     <div class="modal-content">
+       <div class="modal-header">
+         <span class="modal-title" id="modalMemberName">—</span>
+         <span id="modalTier" class="modal-tier"></span>
+         <a href="#" class="modal-close" onclick="event.preventDefault(); document.getElementById('memberModal').classList.remove('active')">[x]</a>
+       </div>
+
+       <div class="modal-section">
+         <div class="modal-section-title">Status by Month</div>
+         <table class="modal-table">
+           <thead><tr><th>Month</th><th>Sessions</th><th>Expected</th><th>Paid</th><th>Status</th></tr></thead>
+           <tbody id="modalStatusBody"></tbody>
+         </table>
+       </div>
+
+       <div class="modal-section" id="modalExceptionSection" style="display:none">
+         <div class="modal-section-title">Exception Overrides</div>
+         <div id="modalExceptionList" class="tx-list"></div>
+       </div>
+
+       <div class="modal-section" id="modalOtherSection" style="display:none">
+         <div class="modal-section-title">Other Payments</div>
+         <div id="modalOtherList" class="tx-list"></div>
+       </div>
+
+       <div class="modal-section">
+         <div class="modal-section-title">Matched Transactions</div>
+         <div id="modalTxList" class="tx-list"></div>
+       </div>
+
+       <div class="modal-section">
+         <div class="modal-section-title">
+           Raw Payments (debug)
+           <a href="#" id="rawPaymentsToggle" class="raw-toggle">[show]</a>
+         </div>
+         <div id="modalRawList" class="tx-list" style="display:none"></div>
+       </div>
+     </div>
+   </div>
+   ```
+
+c. Add the script tag alongside `filters.js`. To tell the module which API
+   endpoint to fetch, use a `data-page` attribute on `body` (or on the
+   filter container — already exists). Simplest: add `data-page="adults"` /
+   `data-page="juniors"` to the existing `<div id="filterContainer">`.
+   The module reads it on load.
+
+   ```gotmpl
+   <script src="/static/js/member-detail.js" defer></script>
+   ```
+
+### 2. Create [go/internal/web/static/js/member-detail.js](go/internal/web/static/js/member-detail.js)
+
+A single shared module — both pages use the same DOM contract, so the same
+JS works for both. Structure (vanilla ES, no build step, matches `filters.js`
+style — IIFE, `'use strict'`, no globals leaked):
+
+```js
+(function () {
+  'use strict';
+
+  const container = document.getElementById('filterContainer');
+  if (!container) return;
+  const page = container.dataset.page;        // "adults" | "juniors"
+  if (!page) return;
+
+  let apiData = null;          // cached /api/<page> response
+  let currentMemberName = null;
+
+  // ── Data load ─────────────────────────────────────────────────────────
+  async function loadData() {
+    if (apiData) return apiData;
+    const r = await fetch('/api/' + page);
+    if (!r.ok) throw new Error('failed to fetch /api/' + page);
+    apiData = await r.json();
+    return apiData;
+  }
+
+  // Pre-warm immediately so first click is instant.
+  loadData().catch(err => console.error('[member-detail]', err));
+
+  // ── Modal render ──────────────────────────────────────────────────────
+  async function showMember(name) { /* port of Python showMemberDetails */ }
+  function toggleRawPayments(ev)  { /* port */ }
+  function closeModal()           { document.getElementById('memberModal').classList.remove('active'); }
+  function navigateMember(dir)    { /* port — walk visible .member-row */ }
+
+  // ── Wiring ────────────────────────────────────────────────────────────
+  document.querySelectorAll('.info-icon[data-name]').forEach(el => {
+    el.addEventListener('click', ev => {
+      ev.stopPropagation();
+      showMember(el.dataset.name);
+    });
+  });
+  document.getElementById('rawPaymentsToggle').addEventListener('click', toggleRawPayments);
+
+  document.addEventListener('keydown', e => {
+    const modal = document.getElementById('memberModal');
+    if (e.key === 'Escape') { closeModal(); return; }
+    if (!modal.classList.contains('active')) return;
+    if (e.key === 'ArrowDown') { e.preventDefault(); navigateMember(1); }
+    if (e.key === 'ArrowUp')   { e.preventDefault(); navigateMember(-1); }
+  });
+}());
+```
+
+The four `port` functions transcribe Python literally, with two adjustments:
+
+- `data.tier` — read directly from the API response (already present as
+  `AdultsMemberData.Tier` / `JuniorsMemberData.Tier`).
+- Junior `expected` may equal the literal string `"?"` (sentinel from
+  `Expected.MarshalJSON`). The status-row formatter must treat string
+  `expected` as "unknown / single attendance" and skip the numeric
+  comparisons — same logic Python uses when it sees `"?"`.
+
+`navigateMember` walks `document.querySelectorAll('tr.member-row')` filtered
+by `style.display !== 'none'`, finds the index whose `dataset.name`
+matches `currentMemberName`, and calls `showMember` on the next/previous
+visible row. Identical to Python lines 944-962 but uses `dataset.name`
+instead of parsing `childNodes[0].textContent`.
+
+### 3. Wire `data-page` attribute
+
+Append `data-page="adults"` to the `filterContainer` div in `adults.tmpl`,
+`data-page="juniors"` in `juniors.tmpl`. One-line edit per template.
+
+### 4. Unit test
+
+Extend [go/internal/web/html_handler_test.go](go/internal/web/html_handler_test.go)
+with assertions that the rendered HTML for `/adults` and `/juniors` contains:
+
+- `class="info-icon"` with the expected `data-name` per fixture row,
+- `id="memberModal"`,
+- `<script src="/static/js/member-detail.js"`,
+- `data-page="adults"` / `data-page="juniors"` on the filter container.
+
+These are markup-level checks only — the JS module behaviour is not unit
+tested in Go (would require headless-browser tooling that is out of scope
+for this milestone). Manual browser verification covers it.
+
+## Critical files
+
+| Action | Path |
+|--------|------|
+| edit   | [go/internal/web/templates/adults.tmpl](go/internal/web/templates/adults.tmpl) — add `[i]` icon, modal markup, `data-page`, script tag |
+| edit   | [go/internal/web/templates/juniors.tmpl](go/internal/web/templates/juniors.tmpl) — same |
+| new    | `go/internal/web/static/js/member-detail.js` — modal module |
+| edit   | `go/internal/web/html_handler_test.go` — markup assertions |
+
+No changes to: `app.css` (already complete), `assets.go` (the `embed.FS`
+glob `static/js/*` already picks up new files), `server.go`, `render.go`,
+the API handlers, or any domain code.
+
+## Reused existing infrastructure
+
+- [go/internal/web/api/handler.go](go/internal/web/api/handler.go) — `/api/adults`, `/api/juniors` already serve the modal's data
+- [go/internal/web/api/adults.go:27-42](go/internal/web/api/adults.go#L27-L42), [go/internal/web/api/juniors.go](go/internal/web/api/juniors.go) — typed responses
+- [go/internal/web/api/types.go:24-29](go/internal/web/api/types.go#L24-L29) — `Expected` "?" sentinel marshalling
+- [go/internal/web/static/css/app.css](go/internal/web/static/css/app.css) — modal CSS already lifted
+- [go/internal/web/static/js/filters.js](go/internal/web/static/js/filters.js) — IIFE / `'use strict'` / `data-*` attribute style to match
+- [templates/adults.html:725-962](templates/adults.html#L725-L962) — Python reference implementation to port (logic, not literal copy)
+
+## Verification
+
+End-to-end:
+
+1. `cd go && make go-build go-test go-lint` — all green.
+2. `make web-go &` — boot Go on `:8080`.
+3. Browser: `http://localhost:8080/adults`
+   - Click `[i]` next to a member name → modal opens with that member's data.
+   - Status table populated; cells colour-coded (cell-ok / cell-unpaid).
+   - Exception section visible only if member has exceptions; exception
+     amount shown with "*" override style.
+   - "Other Payments" section visible only if member has other-purpose
+     transactions.
+   - Matched transactions list newest-first; raw-payments section starts
+     hidden, `[show]` toggles to `[hide]`.
+   - `Esc` closes the modal; `ArrowDown` / `ArrowUp` walk visible rows
+     (after applying name filter).
+   - Click outside the `.modal-content` closes the modal.
+   - Open DevTools Network tab → reload; confirm one request to `/api/adults`
+     fires on page load (data is pre-warmed), no further requests on row
+     click.
+4. Browser: `http://localhost:8080/juniors`
+   - Same checks; verify `expected = "?"` rows render the question-mark
+     status without throwing JS errors.
+5. Cross-check against Python: `make web-py &` → `http://localhost:5001/adults`
+   should look visually equivalent (modulo nav styling) for the same fixture.
+6. After commit: `tea pr create --base main --head feat/go-m6-5-modal-js`.
+
+## Branching
+
+Per [CLAUDE.md](CLAUDE.md): create `feat/go-m6-5-modal-js` off `main`,
+commit with `Co-Authored-By` trailer, push with `-u`, open MR via
+`tea pr create`. Do not merge from CLI. After the user merges in Gitea:
+
+- Add CHANGELOG entry (timestamp via `date "+%Y-%m-%d %H:%M %Z"`).
+- Tick **M6.5** in
+  [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md:117](docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md#L117)
+  with the merge SHA.
+
+## Out of scope (deferred)
+
+- **`/qr` modal** — separate `#qrModal` element, lives in M6.6 alongside
+  `/sync-bank`, `/flush-cache`, `/version`.
+- **Pay buttons inside the modal** — Python's modal does not include
+  Pay-from-modal; current Go pages already render row-level Pay buttons
+  in M6.2/M6.3.
+- **Modal on `/payments`** — Python `/payments` has no modal, neither does
+  Go (confirmed in M6.4 plan).
+- **Deep-linking (`/adults#name=Foo`)** — not in Python, not adding.
+- **Headless-browser JS tests** — out of scope for this milestone; manual
+  browser verification per §Verification.

docs/plans/2026-05-08-1334-go-m6-6-action-pages.md

@@ -0,0 +1,124 @@
+# M6.6 — `/qr`, `/sync-bank`, `/flush-cache`, `/version` (Go parity)
+
+> On approval, relocate this file to `docs/plans/YYYY-MM-DD-HHMM-go-m6-6-action-pages.md` per the repo's `CLAUDE.md` "Plans" convention before starting work.
+
+## Context
+
+The Go-rewrite progress tracker ([2026-05-03-2349-go-backend-rewrite-progress.md:118](docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md#L118)) lists M6.6 as:
+
+> `/qr, /sync-bank, /flush-cache, /version pages`
+
+After M6.4 (payments page) and M6.5 (member-detail modal JS), the only remaining pre-deployment HTML/action endpoints in Python that the Go binary doesn't yet implement are these four. The adults/juniors templates already produce `/qr?...` URLs via the `qrHref` / `qrHrefAll` helpers ([render.go:47-71](go/internal/web/render.go#L47-L71)) — the matching handler is the missing piece. `sync` and `flush_cache` templates exist as "Coming in M6.6" stubs and need real markup + working handlers. `/api/version` already serves build metadata; `/version` just needs to alias it (Python parity).
+
+After M6.6 the M6 gate ("Browser smoke on :8080: all pages render … QR loads, sync/flush work end-to-end") is reachable.
+
+## Confirmed design choices
+
+- **`/sync-bank`**: Python-faithful — GET both renders and triggers the sync, captures stdout/stderr into a log buffer, surfaces success/failure via a flag. Matches existing nav `[Sync Bank Data]` link.
+- **`/version`**: JSON alias of `/api/version`. No HTML page.
+- **QR library**: `github.com/skip2/go-qrcode`. Default level `qrcode.Medium`, size 256.
+
+## Scope per endpoint
+
+### 1. `GET /qr` — PNG only
+
+Match Python ([app.py:321-356](app.py#L321-L356)) verbatim semantics:
+
+1. Read `account` (default `cfg.BankAccount`), `amount` (default `"0"`), `message` (default `""`).
+2. Validate account against `^[A-Z]{2}\d{2,34}$|^\d{1,16}/\d{4}$`; on miss, silently fall back to `cfg.BankAccount`.
+3. Parse amount as float64; clamp to `[0, 10_000_000]`; format `%.2f`; on parse error → `"0.00"`.
+4. Truncate message to 60 runes; strip all `*`.
+5. If account contains `/`, split into `{number}*BC:{bankcode}`; else use raw.
+6. SPD payload: `SPD*1.0*ACC:{acc}*AM:{amount}*CC:CZK*MSG:{msg}` (no `BC:` key when IBAN — Python doesn't either).
+7. `qrcode.Encode(payload, qrcode.Medium, 256)` → write bytes with `Content-Type: image/png`.
+
+No template, no HTML.
+
+### 2. `GET /sync-bank` — triggers + renders
+
+Match Python ([app.py:124-151](app.py#L124-L151)):
+
+1. Build a `*bytes.Buffer` to capture step output.
+2. For each step write a header line then call:
+   - `banksync.SyncToSheets(ctx, cfg.PaymentsSheetID, fioClient, sheetsClient, banksync.SyncOpts{From: jan1ThisYear, To: dec31ThisYear, Sort: true})`
+   - `banksync.InferPayments(ctx, cfg.PaymentsSheetID, sheetsClient, sources, banksync.InferOpts{})`
+   - `cacheFlusher.Flush()` — append `"%d cache files deleted"`.
+3. On any error: append `err.Error()` + a stack trace via `runtime/debug.Stack()`, set `success=false`, continue rendering.
+4. Render `sync` template with `SyncPageData{ PageData; Output string; Success bool }`.
+
+The `banksync` package's stdout-printing functions can be redirected by passing an `io.Writer` — confirm during implementation; if they only print to `os.Stdout`, capture by tee'ing through a `slog` handler or briefly swapping `os.Stdout` (or extend the package with a `*Writer` option). **Preferred**: add a `Logger io.Writer` field to `banksync.SyncOpts` / `InferOpts`. This is a minor extension to existing services, not a rewrite.
+
+### 3. `/flush-cache` — GET form, POST action
+
+Match Python ([app.py:117-122](app.py#L117-L122)):
+
+- `GET` → render `flush_cache` with `Flushed=false`.
+- `POST` → call `cacheFlusher.Flush()`, render with `Flushed=true, Deleted=n`.
+
+### 4. `GET /version` — JSON
+
+One-liner: register the existing `api.VersionHandler` (or its inline equivalent in [api/version.go](go/internal/web/api/version.go)) on the `/version` path as well as `/api/version`. Output: `{"tag", "commit", "build_date"}`.
+
+## Files to create / modify
+
+### New files
+
+- **[go/internal/web/templates/qr.tmpl](go/internal/web/templates/qr.tmpl)** — *not actually needed*; remove from plan if `/qr` is PNG-only. (Decision: skip — no template.)
+- Replace stub **[go/internal/web/templates/sync.tmpl](go/internal/web/templates/sync.tmpl)** with full markup: title, status banner colored by `Success`, `<pre>` of `Output`, "Run again" link.
+- Replace stub **[go/internal/web/templates/flush_cache.tmpl](go/internal/web/templates/flush_cache.tmpl)** with: form (`POST /flush-cache` → `<button>[Flush Cache]</button>`), success banner when `Flushed`.
+
+### Modified files
+
+- **[go/go.mod](go/go.mod)** / `go.sum` — add `github.com/skip2/go-qrcode`.
+- **[go/internal/web/server.go](go/internal/web/server.go)** — register `GET /qr`, `GET /sync-bank` (replace stub), `GET /flush-cache` (form), `POST /flush-cache` (action), `GET /version`. Widen `Run(...)` signature to accept `fio.Client`, `sheets.Client`, and a `cache.Flusher` — these flow into a new `Deps` struct on `HTMLHandler`.
+- **[go/internal/web/html_handler.go](go/internal/web/html_handler.go)** — add `ServeQR`, real `ServeSync`, split `ServeFlushCacheGET` / `ServeFlushCachePOST`, add `ServeVersion` (delegates to api package).
+- **[go/internal/web/render.go](go/internal/web/render.go)** — add `SyncPageData{ PageData; Output string; Success bool }` and `FlushPageData{ PageData; Flushed bool; Deleted int }` view-models. (`pageNames` already includes `"sync"` and `"flush_cache"`; no change.)
+- **[go/internal/web/qr.go](go/internal/web/qr.go)** *(new file)* — pure helper: `BuildSPD(account, amount, message string, defaultAccount string) (payload string)` + `RenderQRCode(payload string) ([]byte, error)`. Easier to unit-test than a method on the handler.
+- **[go/internal/services/membership/loader.go](go/internal/services/membership/loader.go)** — add a small `CacheFlusher` interface (`Flush() (int, error)`); have `Sources` aggregate include it. *Alternative considered*: pass `*cache.FileCache` straight into `web.Run`. Choose whichever needs fewer test-stub edits — likely the direct-pass approach, since stubs in tests don't need cache behavior. **Decision: pass `cache.Flusher` directly into `web.Run` as a separate dependency, not through `Sources`.** Simpler, fewer interface changes.
+- **[go/internal/services/banksync/sync.go](go/internal/services/banksync/sync.go)** + `infer.go` — accept an optional `io.Writer` (in `SyncOpts.Logger` / `InferOpts.Logger`) and route progress prints through it; default to `os.Stdout` when nil for CLI parity.
+- **[go/cmd/fuj/main.go](go/cmd/fuj/main.go)** — in the `server` subcommand, build `fio.Client`, `sheets.Client`, and `cache.Flusher` (already constructed inside `membership.NewSources` — expose it or construct a sibling) and pass them into `web.Run`.
+
+## Reuse (already in the codebase)
+
+- **Bank sync**: `banksync.SyncToSheets` ([go/internal/services/banksync/sync.go](go/internal/services/banksync/sync.go)) and `banksync.InferPayments` ([go/internal/services/banksync/infer.go](go/internal/services/banksync/infer.go)) — same calls the CLI `sync` / `infer` subcommands use ([go/cmd/fuj/main.go:184](go/cmd/fuj/main.go#L184), [:222](go/cmd/fuj/main.go#L222)).
+- **Cache flush**: `(*cache.FileCache).Flush() (int, error)` ([go/internal/io/cache/filecache.go:92](go/internal/io/cache/filecache.go#L92)) — already returns the deleted count.
+- **Build metadata**: `BuildInfo{Version, Commit, BuildDate}` ([go/internal/web/server.go:28-35](go/internal/web/server.go#L28-L35)) is already plumbed everywhere; `/api/version` JSON shape is already correct ([go/internal/web/api/version.go](go/internal/web/api/version.go)).
+- **Template render pattern**: `Renderer.Render(w, name, data)` ([go/internal/web/render.go:98-108](go/internal/web/render.go#L98-L108)).
+- **Test scaffolding**: `web.NewRenderer()` + `httptest.NewRequest/NewRecorder` ([go/internal/web/html_handler_test.go:52-94](go/internal/web/html_handler_test.go#L52-L94)).
+
+## Tests
+
+Add to `go/internal/web/html_handler_test.go` (and one new `qr_test.go` for the SPD builder):
+
+- **`TestQRBuildSPD`** *(unit, in [go/internal/web/qr_test.go](go/internal/web/qr_test.go))* — table-driven: invalid account → fallback; `/`-account → `{num}*BC:{bc}`; IBAN → raw; amount `-1` → `0.00`; amount `99999999` → `9999999.00`; amount `"abc"` → `0.00`; message with `*` stripped; message length-clamped to 60.
+- **`TestServeQR`** — request `/qr?account=…&amount=10&message=Hi`; assert 200, `Content-Type: image/png`, body starts with PNG magic `\x89PNG\r\n\x1a\n`.
+- **`TestServeFlushCacheGet`** — assert form rendered, no banner.
+- **`TestServeFlushCachePost`** — fixture flusher returns 3; assert banner says "3" and `Flushed`.
+- **`TestServeSync`** — fixture banksync stubs return `(2, nil)` and `(1, nil)`, fixture flusher returns 4; assert page renders, status is success, output contains the section headers.
+- **`TestServeVersion`** — assert `application/json`, body `{"tag":"v0","commit":"abc1234","build_date":"2026-01-01"}`.
+- Extend the `TestHTMLHandlerSmoke` table to cover `/qr` and `/version`.
+
+## Verification (end-to-end)
+
+1. `cd go && go build ./... && go test ./...`
+2. `cd go && go run ./cmd/fuj server` — open http://localhost:8080
+3. Smoke:
+   - **/adults** → click `Pay` next to any unpaid month → modal shows QR image (this exercises `/qr`). Confirm a Czech banking app can scan it (visual check).
+   - Direct `/qr?account=2702008874/2010&amount=700&message=Test` → PNG renders.
+   - **/sync-bank** → click `[Sync Bank Data]` in nav → page shows "Syncing…", then sections + "Inferred Payments", "Cache Flushed", green status banner.
+   - **/flush-cache** → click `[Flush Cache]` → success banner with file count.
+   - **/version** in browser → JSON visible.
+   - Adults / juniors / payments still render (no regressions from `Run` signature change).
+4. Run the parity diff: `go run ./cmd/parity` — `/api/version` must still match Python.
+5. Append a CHANGELOG entry per `CLAUDE.md`; tick `M6.6` in [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md:118](docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md#L118).
+
+## Branch / MR
+
+Per `CLAUDE.md` workflow: `feat/go-m6-6-action-pages` off `main`, push with `-u`, open with `tea pr create --base main --head feat/go-m6-6-action-pages`.
+
+## Out of scope (deferred)
+
+- Auth / CSRF protection on `/sync-bank` and `/flush-cache` — Python has none either; deferred to M8 hardening.
+- M6.7 (single-binary embed verification) — separate ticket.
+- Streaming progress for `/sync-bank` (currently buffered until completion, like Python).
+- Configurable QR error-correction level / size.

docs/plans/2026-05-08-1439-go-m6-6-1-payment-qr-modal.md

@@ -0,0 +1,335 @@
+# M6.6.1 — Pay-button QR popup modal (`/adults`, `/juniors`)
+
+> Plan-mode note: per project convention this plan should live at
+> `docs/plans/2026-05-08-1439-go-m6-6-1-payment-qr-modal.md`. The first
+> execution step after approval is to copy this file there.
+> Branch: `feat/go-m6-6-1-payment-qr-modal` off `main`.
+
+## Context
+
+M6.6 ([docs/plans/2026-05-08-1334-go-m6-6-action-pages.md](docs/plans/2026-05-08-1334-go-m6-6-action-pages.md))
+landed the backend `/qr` PNG endpoint plus `/sync-bank`, `/flush-cache`,
+`/version`. While doing it, the **client-side** half of the Pay flow was
+collapsed from a modal-with-details into a plain `<a href="/qr?...">` —
+clicking Pay now navigates the whole tab to the raw PNG.
+
+The Python app instead opens an in-page `#qrModal` showing the QR image
+*plus* labelled details (account, amount, message, title), then closes
+the modal on outside-click or `[close]`
+([templates/adults.html:631-648](templates/adults.html#L631-L648),
+JS at [templates/adults.html:963-993](templates/adults.html#L963-L993)).
+This is the UX the user expects from the dashboard — staying on the
+table while displaying the QR is significantly more practical than
+losing context to a fullscreen image.
+
+M6.6.1 restores parity: the Pay/Pay-All buttons open an in-page
+`#qrModal`, identical in structure to the Python original, driven by a
+new vanilla-JS module `payment-qr.js` that mirrors the `member-detail.js`
+convention from M6.5.
+
+All the building blocks are already in place:
+
+- **`/qr` endpoint** ships PNGs ([go/internal/web/qr.go](go/internal/web/qr.go), tested by [TestServeQR](go/internal/web/html_handler_test.go#L207-L231)).
+- **CSS** for `#qrModal .modal-content`, `.qr-image`, `.qr-details` is
+  already in [go/internal/web/static/css/app.css:445-478](go/internal/web/static/css/app.css#L445-L478) — lifted during M6.1.
+- **Template helpers** `qrHref` / `qrHrefAll` ([go/internal/web/render.go:63-85](go/internal/web/render.go#L63-L85))
+  already produce the correct query string + Czech `MM/YYYY` format
+  for the `message=` param. They're useful for sanity (and for any
+  no-JS fallback) but become dead code post-M6.6.1 — see §Out of scope.
+- **Bank account** is already exposed as `$.Data.BankAccount` to every
+  template that has a Pay button.
+- **JS module convention**: `member-detail.js` is the M6.5 baseline —
+  IIFE, `'use strict'`, event delegation off `data-*` attributes, no
+  inline `onclick`, no globals leaked.
+
+## Approach
+
+### 1. Replace `<a href="{{qrHref ...}}">` with `<button data-...>`
+
+In [go/internal/web/templates/adults.tmpl](go/internal/web/templates/adults.tmpl)
+and [go/internal/web/templates/juniors.tmpl](go/internal/web/templates/juniors.tmpl)
+(both have identical Pay markup at lines 65 and 72):
+
+```gotmpl
+<button type="button" class="pay-btn"
+        data-name="{{$row.Name}}"
+        data-amount="{{$cell.Amount}}"
+        data-month="{{$cell.Month}}"
+        data-raw-month="{{$cell.RawMonth}}">Pay</button>
+```
+
+```gotmpl
+<button type="button" class="pay-btn"
+        data-name="{{$row.Name}}"
+        data-amount="{{$row.PayableAmount}}"
+        data-month="{{$row.UnpaidPeriods}}"
+        data-raw-month="{{$row.RawUnpaidPeriods}}"
+        data-pay-all="1">Pay All</button>
+```
+
+Why `<button type="button">` and not `<a>`: the click no longer
+navigates — the JS handles it. `type="button"` prevents accidental form
+submission. A no-JS fallback could be added later by re-introducing
+`href="{{qrHref ...}}"` and letting the JS call `e.preventDefault()` —
+deferred until anyone actually asks (see §Out of scope).
+
+`data-month` carries the human-readable period (e.g. `January 2026`,
+or `January 2026 + February 2026` for Pay-All) which the modal title
+displays. `data-raw-month` carries the machine format (`2026-01`,
+`2026-01+2026-02`) which the JS converts to `MM/YYYY` for the QR
+message — same conversion Python's `showPayQR` does at
+[templates/adults.html:966-968](templates/adults.html#L966-L968).
+`data-pay-all` is purely informational; the JS doesn't actually need
+it (the same code path handles single + multi-period), but keeping it
+helps debugging and any future analytics.
+
+### 2. Add `#qrModal` markup
+
+Append after the `#memberModal` block in both `adults.tmpl` and
+`juniors.tmpl` (around line 185 of adults, line 165 of juniors), mirroring
+[templates/adults.html:631-648](templates/adults.html#L631-L648) but
+using `class="active"` toggling (the convention M6.5 picked) instead of
+`style.display = 'block'`:
+
+```gotmpl
+<div id="qrModal" onclick="if(event.target===this)this.classList.remove('active')">
+  <div class="modal-content">
+    <div class="modal-header">
+      <div class="modal-title" id="qrTitle">Payment for —</div>
+      <div class="close-btn" onclick="document.getElementById('qrModal').classList.remove('active')">[close]</div>
+    </div>
+    <div class="qr-image">
+      <img id="qrImg" src="" alt="Payment QR Code">
+    </div>
+    <div class="qr-details">
+      <div>Account: <span id="qrAccount"></span></div>
+      <div>Amount: <span id="qrAmount"></span> CZK</div>
+      <div>Message: <span id="qrMessage"></span></div>
+    </div>
+  </div>
+</div>
+```
+
+The CSS already targets `#qrModal .modal-content` directly. To make the
+"hidden by default / visible when `.active`" toggle behave the same
+way `#memberModal` does, the existing CSS rules for `#memberModal`
+(`display:none`, `#memberModal.active { display: flex; }`) need a
+sibling pair for `#qrModal`. Audit `app.css` during implementation:
+- if `#qrModal` already has both rules, no change.
+- if it has only `display:none`, add `#qrModal.active { display: flex; }`.
+- if it has neither, add both.
+
+This is a 2-line CSS adjustment at most; tracked under §Critical files.
+
+### 3. Bank account on the page
+
+The modal needs the bank account string for the `qrAccount` label and
+for building the `/qr?account=…` URL. Two clean options:
+
+**(a)** Read it from the `<button>`'s `data-bank-account` attribute.
+Per-button duplication, but trivially done in templates and keeps the JS
+module's surface tiny.
+
+**(b)** Stamp it once on the page as `<body data-bank-account="…">`
+(or on the existing `#filterContainer`).
+
+**Decision: (b)** — single stamping site, follows the same pattern
+M6.5 used for `data-page` on `#filterContainer`. Add
+`data-bank-account="{{.Data.BankAccount}}"` to `#filterContainer` in
+both templates (one-line edit each).
+
+### 4. Create [go/internal/web/static/js/payment-qr.js](go/internal/web/static/js/payment-qr.js)
+
+A new module loaded with `<script src="/static/js/payment-qr.js" defer></script>`
+right after `member-detail.js` in both templates. Pure ES, no build
+step, IIFE, `'use strict'`. Skeleton — port of Python's `showPayQR`
+([templates/adults.html:963-986](templates/adults.html#L963-L986))
+plus event wiring:
+
+```js
+(function () {
+  'use strict';
+
+  const container = document.getElementById('filterContainer');
+  if (!container) return;
+  const bankAccount = container.dataset.bankAccount || '';
+
+  const modal      = document.getElementById('qrModal');
+  const titleEl    = document.getElementById('qrTitle');
+  const imgEl      = document.getElementById('qrImg');
+  const accountEl  = document.getElementById('qrAccount');
+  const amountEl   = document.getElementById('qrAmount');
+  const messageEl  = document.getElementById('qrMessage');
+  if (!modal || !titleEl || !imgEl || !accountEl || !amountEl || !messageEl) return;
+
+  // Convert "YYYY-MM" → "MM/YYYY"; "+"-joined ranges are converted piece-wise.
+  // Mirrors templates/adults.html:966-968.
+  function toCzechMonth(rawMonth) {
+    return rawMonth.split('+')
+      .map(p => p.replace(/^(\d{4})-(\d{2})$/, '$2/$1'))
+      .join('+');
+  }
+
+  function showQR(name, amount, month, rawMonth) {
+    const numericMonth = toCzechMonth(rawMonth);
+    const message = `${name}: ${numericMonth}`;
+
+    titleEl.innerText   = `Payment for ${month}`;
+    accountEl.innerText = bankAccount;
+    amountEl.innerText  = amount;
+    messageEl.innerText = message;
+
+    const url = '/qr?'
+      + 'account=' + encodeURIComponent(bankAccount)
+      + '&amount=' + encodeURIComponent(amount)
+      + '&message=' + encodeURIComponent(message);
+    imgEl.src = url;
+
+    modal.classList.add('active');
+  }
+
+  function closeQR() { modal.classList.remove('active'); }
+
+  // Event delegation: any .pay-btn click anywhere in the page.
+  document.addEventListener('click', ev => {
+    const btn = ev.target.closest('.pay-btn');
+    if (!btn) return;
+    ev.preventDefault();
+    showQR(
+      btn.dataset.name,
+      btn.dataset.amount,
+      btn.dataset.month,
+      btn.dataset.rawMonth,
+    );
+  });
+
+  document.addEventListener('keydown', e => {
+    if (e.key === 'Escape' && modal.classList.contains('active')) closeQR();
+  });
+}());
+```
+
+Notes:
+
+- **Event delegation** (single listener on `document`) handles both Pay
+  and Pay-All without enumerating buttons. It also survives any future
+  re-render of the table without needing rebinding.
+- **Coexistence with `member-detail.js`**: `member-detail.js` listens
+  for `Escape` too, but only acts when `#memberModal` is active; the
+  new module similarly only acts when `#qrModal` is active. No collision.
+- **Pre-warming**: nothing to pre-warm — `/qr` is a tiny on-demand PNG
+  and only fires when the user clicks.
+- **Inline `onclick`** on `[close]` and outside-click in the markup are
+  carried over from the M6.5 modal style; consistent with `#memberModal`.
+  (Switching the project's modal close pattern to data attributes is a
+  separate cleanup, out of scope here.)
+
+### 5. Tests
+
+Extend [go/internal/web/html_handler_test.go](go/internal/web/html_handler_test.go)
+with markup-level checks. Headless-browser JS is out of scope (same
+rationale as M6.5).
+
+In `TestModalMarkup` (or a sibling test, e.g. `TestPaymentQRMarkup`):
+
+- Body for `/adults` and `/juniors` contains
+  `<script src="/static/js/payment-qr.js"`.
+- Body contains `id="qrModal"`, `id="qrImg"`, `id="qrAccount"`,
+  `id="qrAmount"`, `id="qrMessage"`, `id="qrTitle"`.
+- The fixture row's Pay button is rendered as
+  `<button … class="pay-btn" … data-name="Test Member" data-amount="…" data-raw-month="2026-01"`.
+- The fixture row's `.pay-btn` does **not** include `href=`.
+- `#filterContainer` has `data-bank-account="CZ0000000000000000000000"`
+  (matching the test's `fixtureHandler` config).
+
+### 6. Decide fate of `qrHref` / `qrHrefAll` template helpers
+
+Once Pay/Pay-All buttons are JS-driven, the helpers in
+[render.go:63-85](go/internal/web/render.go#L63-L85) have no callers.
+**Decision: delete them**, plus their entries in `tmplFuncs`. A
+no-JS fallback is not on the roadmap; if it ever becomes one, the
+helpers are easy to resurrect from git.
+
+The unit-test file currently has no direct tests for these helpers —
+nothing to remove from tests.
+
+## Critical files
+
+| Action | Path |
+|--------|------|
+| edit   | [go/internal/web/templates/adults.tmpl](go/internal/web/templates/adults.tmpl) — Pay/Pay-All → `<button data-…>`; add `#qrModal`; add `data-bank-account` on filter container; add `<script src="/static/js/payment-qr.js" defer>` |
+| edit   | [go/internal/web/templates/juniors.tmpl](go/internal/web/templates/juniors.tmpl) — same |
+| new    | `go/internal/web/static/js/payment-qr.js` — modal module |
+| edit   | [go/internal/web/render.go](go/internal/web/render.go) — drop `qrHref`, `qrHrefAll`, and their `tmplFuncs` entries (and the `net/url`, `strconv` imports if no longer needed) |
+| edit   | [go/internal/web/static/css/app.css](go/internal/web/static/css/app.css) — verify / add `#qrModal { display:none; }` + `#qrModal.active { display:flex; }` rules |
+| edit   | [go/internal/web/html_handler_test.go](go/internal/web/html_handler_test.go) — markup assertions |
+
+No changes to: `assets.go` (`embed.FS` glob picks up new JS automatically),
+`server.go`, `html_handler.go`, the `/qr` handler, `cmd/fuj/main.go`, the
+API handlers, or any domain code.
+
+## Reused existing infrastructure
+
+- [go/internal/web/qr.go](go/internal/web/qr.go) — `/qr?account=…&amount=…&message=…` endpoint serves the PNG already
+- [go/internal/web/static/css/app.css:445-478](go/internal/web/static/css/app.css#L445-L478) — modal CSS already lifted whole
+- [go/internal/web/static/js/member-detail.js](go/internal/web/static/js/member-detail.js) — IIFE / `'use strict'` / `data-*` style to mirror
+- [go/internal/web/api/types.go](go/internal/web/api/types.go) — `MemberRow.UnpaidPeriods` and `RawUnpaidPeriods` already populated for Pay-All
+- [templates/adults.html:631-648,963-986](templates/adults.html#L631-L648) — Python reference for both modal markup and `showPayQR` JS (logic to port, not literal copy)
+
+## Verification
+
+End-to-end, after copying the plan into `docs/plans/`:
+
+1. `cd go && make go-build go-test go-lint` — all green.
+2. `make web-go &` — boot Go on `:8080`.
+3. Browser: `http://localhost:8080/adults`
+   - Click `Pay` on any unpaid month → `#qrModal` opens with
+     - title `Payment for <Month YYYY>`,
+     - `qrAccount` matching `BANK_ACCOUNT`,
+     - `qrAmount` matching the cell amount,
+     - `qrMessage` formatted as `<Name>: MM/YYYY`,
+     - QR image rendered from `/qr?…` (Network tab shows PNG response).
+   - Tab does **not** navigate; URL stays `/adults`.
+   - Click `Pay All` → modal opens with `+`-joined `MM/YYYY+MM/YYYY` message.
+   - Click outside the modal-content → modal closes.
+   - Click `[close]` → modal closes.
+   - Press `Esc` → modal closes.
+   - Open `[i]` member-detail modal first, then `Esc` → only that closes
+     (verify both modals don't fight each other).
+4. Browser: `http://localhost:8080/juniors` — same checks. Verify Pay
+   on a `"?"`-expected row doesn't appear (Pay button is conditional on
+   `unpaid`/`partial` cells).
+5. Cross-check against Python: `make web-py &` →
+   `http://localhost:5001/adults` modal looks visually equivalent for
+   the same fixture (modulo any nav / theme differences already accepted
+   in M6).
+6. Scan a QR with a Czech banking app (or `zbarimg` on the saved PNG) —
+   payload starts with `SPD*1.0*ACC:` and the message decodes to
+   `<Name>: MM/YYYY`.
+7. After the user merges in Gitea: append CHANGELOG entry (timestamp via
+   `date "+%Y-%m-%d %H:%M %Z"`); add a new tick line for **M6.6.1** in
+   [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md)
+   immediately under the M6.6 line, in the same format as the other
+   sub-bullets.
+
+## Branching
+
+Per [CLAUDE.md](CLAUDE.md): create `feat/go-m6-6-1-payment-qr-modal` off
+`main`, commit with `Co-Authored-By` trailer, push with `-u`, open MR via
+`tea pr create`. Do not merge or delete from CLI.
+
+## Out of scope (deferred)
+
+- **Pay button no-JS fallback** — feasible to keep `qrHref` and have
+  the JS `preventDefault` an `<a>`, but no current need. Resurrect the
+  helpers if asked.
+- **Modal pattern unification** — `#memberModal` and `#qrModal` use
+  inline `onclick` for `[close]` and outside-click. Consistent with
+  M6.5 but worth a follow-up to delegate-event everything.
+- **Pay-from-modal inside `#memberModal`** — Python doesn't have it, and
+  no one's asked for it on the Go side.
+- **Per-button QR error-correction / size** — `/qr` is fixed at
+  Medium/256, same as M6.6. Configurable via query param can be added if
+  printing larger physical posters becomes a use case.
+- **`/payments` Pay buttons** — the payments page is a ledger view; it
+  doesn't render Pay buttons in either backend.

docs/plans/2026-05-08-1457-go-m6-7-single-binary-embed-verify.md

@@ -0,0 +1,184 @@
+# M6.7 — Single-binary embed verification
+
+## Context
+
+M6.7 is the final task in M6 (Go-native HTML frontend). Per the
+[progress tracker](2026-05-03-2349-go-backend-rewrite-progress.md): "Wire
+`embed.FS` into handlers; verify single-binary deployment includes all
+assets."
+
+The wiring is **already in place** from M6.1 onward:
+
+- [go/internal/web/assets.go](../../go/internal/web/assets.go) declares
+  `//go:embed templates` → `templateFS` and `//go:embed static` → `staticFS`.
+- [go/internal/web/render.go:66](../../go/internal/web/render.go#L66)
+  parses every page template via `template.New(...).ParseFS(templateFS, ...)`.
+- [go/internal/web/server.go:48-68](../../go/internal/web/server.go#L48-L68)
+  serves `/static/*` via `http.FileServerFS(fs.Sub(staticFS, "static"))`.
+- [go/build/Dockerfile](../../go/build/Dockerfile) copies only the compiled
+  binary into the `alpine:3` runtime image — no `templates/` or `static/`
+  directory ever lands beside it.
+
+What is missing is **proof** the embed is complete and stays complete:
+
+1. Nothing fails the build/test if a contributor adds a new file under
+   `internal/web/templates/` or `internal/web/static/` that isn't matched
+   by an `//go:embed` glob (or, more realistically, adds a sibling
+   directory like `static/img/` and the glob still picks it up — but a
+   typo'd directive would silently drop it).
+2. No automated test exercises the `/static/*` route against the embedded
+   FS — current tests in
+   [html_handler_test.go](../../go/internal/web/html_handler_test.go)
+   render templates (which proves `templateFS` is good) but never hit a
+   static URL through the mux.
+3. The "single binary, no working-dir assets" property is undocumented —
+   if it ever broke, no one would notice until the Docker image started
+   500'ing in prod.
+
+The intended outcome: a small test file plus a documented manual
+verification step, after which M6.7 can be ticked and M6 closed.
+
+## Plan
+
+### 1. Add `go/internal/web/assets_test.go`
+
+One new file, two tests, no production code changes.
+
+**Test A — embed completeness regression guard.** Walks the on-disk
+`templates/` and `static/` directories and asserts every regular file is
+also present in the corresponding embedded FS. Catches:
+
+- A new template added without updating the `//go:embed` directive
+  (current globs are `templates` and `static` — recursive by default for
+  directories, so this is a low-probability regression, but the test
+  doubles as living documentation of the contract).
+- A typo in the directive (e.g. someone renames `static` → `assets` in
+  one place but not the other).
+
+Implementation sketch:
+
+```go
+func TestEmbedCompleteness(t *testing.T) {
+    cases := []struct {
+        name   string
+        diskFS fs.FS         // os.DirFS("templates") / os.DirFS("static")
+        embed  fs.FS         // exported helper or via internal test in package web
+        root   string
+    }{...}
+    for _, tc := range cases {
+        _ = fs.WalkDir(tc.diskFS, ".", func(path string, d fs.DirEntry, err error) error {
+            if err != nil || d.IsDir() { return err }
+            embPath := tc.root + "/" + path
+            if _, err := fs.Stat(tc.embed, embPath); err != nil {
+                t.Errorf("file %q on disk but missing in embed.FS: %v", embPath, err)
+            }
+            return nil
+        })
+    }
+}
+```
+
+Because `templateFS` and `staticFS` are unexported package vars, this
+test lives in `package web` (not `web_test`) — sibling to
+[assets.go](../../go/internal/web/assets.go). All the existing handler
+tests are in `package web_test`; that's fine, this one is internal.
+
+**Test B — `/static/*` end-to-end via the mux.** Builds an `http.ServeMux`
+with the same wiring as
+[server.go:68](../../go/internal/web/server.go#L68), fires httptest
+requests, asserts:
+
+- `GET /static/css/app.css` → 200, `Content-Type: text/css; charset=utf-8`,
+  body contains a known string from app.css (e.g. a CSS selector).
+- `GET /static/js/member-detail.js` → 200, `Content-Type` starts with
+  `text/javascript` or `application/javascript`, body non-empty.
+- `GET /static/js/payment-qr.js` → 200, body non-empty.
+- `GET /static/css/missing.css` → 404 (sanity: the file server actually
+  rejects unknown paths instead of returning some default).
+
+Rather than duplicate the mux assembly, factor a tiny helper (or test the
+existing mux). The cleanest move: extract `staticHandler()` from
+[server.go:48-50,68](../../go/internal/web/server.go#L48-L68) into a small
+exported-from-package function or just `staticFS` / `fs.Sub` helper, and
+have the test call it. Smallest delta: keep production code unchanged and
+replicate the two-line wiring inside the test file (acceptable — it's
+two lines and the test exists precisely to lock that contract).
+
+### 2. Manual / one-shot verification (no code; documented in plan only)
+
+Run once locally and tick M6.7. Command transcript:
+
+```bash
+make go-build                  # → ./bin/fuj
+cp bin/fuj /tmp/fuj-standalone
+cd /tmp                        # working dir has no templates/ or static/
+./fuj-standalone server &
+SERVER_PID=$!
+sleep 1
+curl -sf http://localhost:8080/adults | grep -q "Adults Dashboard"
+curl -sf http://localhost:8080/juniors | grep -q "Juniors"
+curl -sf http://localhost:8080/payments | grep -q "Payments Ledger"
+curl -sf -o /tmp/app.css http://localhost:8080/static/css/app.css \
+  && test -s /tmp/app.css
+curl -sf -o /tmp/qr.js http://localhost:8080/static/js/payment-qr.js \
+  && test -s /tmp/qr.js
+kill $SERVER_PID
+```
+
+`fuj server` will fail to talk to Sheets without credentials, so the
+`/adults` etc. pages will render with the `Error` field set — that's
+fine; the assertion is that the **template + static asset pipeline** is
+self-contained, not that data loads. Each curl above only checks for
+markup present in every render path (header text and stylesheet body).
+
+### 3. Tracker + changelog
+
+- Tick `M6.7` in
+  [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md:120](2026-05-03-2349-go-backend-rewrite-progress.md#L120),
+  append the merge SHA on the line.
+- Mark "Last updated" date and bump milestone status: M6 complete, next is
+  M7.
+- Append a `CHANGELOG.md` entry per CLAUDE.md convention (`date "+%Y-%m-%d %H:%M %Z"`).
+
+## Files touched
+
+| File | Change |
+| --- | --- |
+| [go/internal/web/assets_test.go](../../go/internal/web/assets_test.go) | **new** — two tests (embed completeness + `/static/*` mux) |
+| [docs/plans/2026-05-03-2349-go-backend-rewrite-progress.md](2026-05-03-2349-go-backend-rewrite-progress.md) | tick M6.7, bump "last updated" |
+| [CHANGELOG.md](../../CHANGELOG.md) | new top entry |
+
+No production source files change. (If extracting the static handler
+reads cleaner, a 4-line refactor in
+[server.go](../../go/internal/web/server.go) is acceptable but optional.)
+
+## Branch + MR
+
+Per project convention this is a feature, so:
+
+```bash
+git checkout -b feat/go-m6-7-embed-verify
+# … commits …
+git push -u origin feat/go-m6-7-embed-verify
+tea pr create --title "feat(go): M6.7 — single-binary embed verification" \
+  --description "<short body referencing M6.7>" --base main \
+  --head feat/go-m6-7-embed-verify
+```
+
+## Verification
+
+After implementation:
+
+1. `make go-test` → green (new `TestEmbedCompleteness` and `TestStaticAssetsServed` pass).
+2. `make go-lint` → clean.
+3. Run the manual transcript in §2 above — all curls succeed, no
+   "template not found" or 404 on static assets.
+4. `make go-build && docker build -f go/build/Dockerfile -t fuj-go:m6-7 go/` →
+   succeeds; `docker run --rm -p 8080:8080 fuj-go:m6-7` serves `/adults`
+   with stylesheet attached (visual smoke test in browser).
+
+## Out of scope
+
+- Re-architecting how templates are parsed or served.
+- Compressing / fingerprinting static assets (a separate concern).
+- Live integration test with real Sheets data — covered later in M7.

docs/plans/2026-05-11-2353-fill-first-multi-month-allocation.md

@@ -0,0 +1,184 @@
+# Fill-first multi-month payment allocation
+
+## Context
+
+Matyáš Thér paid in two transactions:
+
+| # | Amount | Purpose             |
+|---|--------|---------------------|
+| 1 | 200    | `2026-02`           |
+| 2 | 550    | `2026-02, 2026-03`  |
+
+Total 750 = his expected fee for the two months (likely 2026-02 = 500, 2026-03 = 250 — junior tier or exception-adjusted). The app currently shows 2026-02 = **566** paid, 2026-03 = **183** paid. The user wants:
+
+> First use the second payment for the rest of 2026-02 (no more, no less), then put the remainder toward 2026-03.
+
+Both Python ([scripts/match_payments.py](scripts/match_payments.py)) and Go ([go/internal/domain/reconcile/reconcile.go](go/internal/domain/reconcile/reconcile.go)) have the same bug: when a single transaction's `in_window_share` is less than the sum of in-window expected fees, both fall into a **proportional** branch that splits the new transaction across months in proportion to each month's *total* expected fee — never consulting what prior transactions already paid into earlier months.
+
+Trace for txn 2:
+
+- `in_window = [(2026-02, 500), (2026-03, 250)]`, `total_expected = 750`, `in_window_share = 550`.
+- `550 < 750` → proportional:
+  - 02 alloc = `550 × 500 / 750 = 366.67`
+  - 03 alloc = `550 − 366.67 = 183.33`
+- Combined with txn 1's 200 → 02 = 566.67, 03 = 183.33 → display `566 / 183`. ✓ matches reported numbers.
+
+The fix: replace the greedy + proportional branches with a single **fill-first** loop that iterates `in_window` in user-supplied order (already chronological by convention from [scripts/infer_payments.py:151](scripts/infer_payments.py#L151)) and allocates `min(remaining, max(0, expected − paid_so_far))` to each month, with any final surplus going to the credit bucket. This collapses three cases (greedy / proportional / pure overflow) into one and naturally consults the ledger's `paid` field which is already updated by prior transactions in the same reconcile pass.
+
+The even-split branch (`total_expected == 0`, prepayment before fees known) stays untouched — different semantic, folding it in would silently change behavior.
+
+## Changes
+
+### Python — [scripts/match_payments.py:471-498](scripts/match_payments.py#L471-L498)
+
+Replace both `total_expected > 0` branches (current lines 471–498) with a single unified loop. Keep lines 466–469 above and the even-split fallback below (lines 499–510) as-is.
+
+```python
+            if total_expected > 0:
+                # Fill-first: iterate in_window in matched_months order (chronological by
+                # convention), allocate min(remaining, deficit) to each month, where
+                # deficit accounts for prior transactions already credited to that month.
+                # Any surplus after all in-window deficits are covered → credit bucket.
+                remaining = in_window_share
+                for m, exp in in_window:
+                    paid_so_far = ledger[member_name][m]["paid"]
+                    deficit = max(0.0, float(exp) - paid_so_far)
+                    alloc = min(remaining, deficit)
+                    if alloc <= 0:
+                        continue
+                    ledger[member_name][m]["paid"] += alloc
+                    ledger[member_name][m]["transactions"].append({
+                        "amount": alloc,
+                        "date": tx["date"],
+                        "sender": tx["sender"],
+                        "message": tx["message"],
+                        "confidence": confidence,
+                    })
+                    remaining -= alloc
+                if remaining > 0:
+                    credits[member_name] = credits.get(member_name, 0) + int(remaining)
+            else:
+                # … existing even-split branch (lines 499–510) unchanged …
+```
+
+Note: skipping the `transactions.append` when `alloc <= 0` (e.g. month already fully paid by a prior txn) avoids zero-amount ghost rows in the per-month transaction list. This is a small UI-visible side effect; before committing, grep tests for assertions on `len(transactions)` per month to confirm nothing relies on the current "one row per (txn, month) regardless of alloc" behavior.
+
+### Go — [go/internal/domain/reconcile/reconcile.go:320-357](go/internal/domain/reconcile/reconcile.go#L320-L357)
+
+Same shape — replace both `totalExpected > 0` branches. Even-split branch (lines 358–372) stays.
+
+```go
+            if totalExpected > 0 {
+                // Fill-first; see Python reconcile() for rationale.
+                remaining := inWindowShare
+                for _, mw := range inWindow {
+                    md := ledger[memberName][mw.month]
+                    deficit := float64(mw.expected) - md.Paid
+                    if deficit < 0 {
+                        deficit = 0
+                    }
+                    alloc := remaining
+                    if deficit < alloc {
+                        alloc = deficit
+                    }
+                    if alloc <= 0 {
+                        continue
+                    }
+                    md.Paid += alloc
+                    md.Transactions = append(md.Transactions, TxEntry{
+                        Amount:     alloc,
+                        Date:       tx.Date,
+                        Sender:     tx.Sender,
+                        Message:    tx.Message,
+                        Confidence: string(m.Confidence),
+                    })
+                    ledger[memberName][mw.month] = md
+                    remaining -= alloc
+                }
+                if remaining > 0 {
+                    credits[memberName] += int(remaining)
+                }
+            } else {
+                // … existing even-split branch (lines 358–372) unchanged …
+            }
+```
+
+### Tests
+
+#### Python — [tests/test_reconcile_exceptions.py](tests/test_reconcile_exceptions.py)
+
+1. **Rewrite `test_proportional_underpayment`** ([line 96](tests/test_reconcile_exceptions.py#L96)) — its current assertions (`paid_02 < 750`, `paid_03 < 350`, `paid_04 < 750`, and 02/04 equal allocation) are incompatible with fill-first. Under fill-first with the same fixture (1250 across `02:750, 03:350, 04:750`):
+   - 02: `min(1250, 750) = 750` (full) → remaining 500
+   - 03: `min(500, 350) = 350` (full) → remaining 150
+   - 04: `min(150, 750) = 150` (partial) → remaining 0
+   
+   Replace assertions with these exact expected values, rename to `test_underpayment_fills_earliest_first`.
+
+2. **Add `test_fill_first_across_two_transactions`** — the Matyáš regression:
+
+   ```python
+   def test_fill_first_across_two_transactions(self):
+       """Prior txn fills 02 partially; later txn finishes 02 then spills to 03."""
+       members = [('Matyáš', 'A', {'2026-02': (500, 2), '2026-03': (250, 1)})]
+       sorted_months = ['2026-02', '2026-03']
+       tx1 = _tx('Matyáš', '2026-02', 200)
+       tx2 = _tx('Matyáš', '2026-02, 2026-03', 550)
+
+       result = reconcile(members, sorted_months, [tx1, tx2])
+       months = result['members']['Matyáš']['months']
+
+       self.assertAlmostEqual(months['2026-02']['paid'], 500, places=2)
+       self.assertAlmostEqual(months['2026-03']['paid'], 250, places=2)
+   ```
+
+3. `test_greedy_exact_match`, `test_greedy_overpayment_goes_to_credit`, `test_single_month_unchanged`, `test_two_members_multi_month` should pass unchanged — fill-first agrees with greedy when payment ≥ total expected.
+
+#### Go — [go/internal/domain/reconcile/reconcile_test.go](go/internal/domain/reconcile/reconcile_test.go)
+
+- Add `TestUnderpaymentFillsEarliestFirst` mirroring the rewritten Python test.
+- Add `TestFillFirstAcrossTwoTransactions` mirroring the Matyáš scenario.
+
+#### Parity — [go/tests/parity/reconcile/reconcile_parity_test.go](go/tests/parity/reconcile/reconcile_parity_test.go)
+
+Add a fixture for the Matyáš two-transaction case. Since both implementations change together and Python remains canonical, existing parity fixtures should continue to pass; verify after edits.
+
+### Changelog — [CHANGELOG.md](CHANGELOG.md)
+
+Append top entry (use `date "+%Y-%m-%d %H:%M %Z"` at commit time):
+
+```markdown
+## 2026-05-11 23:55 CET — fill-first multi-month payment allocation
+
+- Multi-month payment allocation now fills the earliest in-window deficit first
+  and spills the remainder to later months, accounting for prior transactions'
+  contributions. Previously a single transaction was split proportionally to
+  each month's total expected fee, ignoring earlier payments — surfaced by
+  Matyáš Thér's two-payment 200+550 case showing 566/183 instead of 500/250.
+- scripts/match_payments.py, go/internal/domain/reconcile/reconcile.go, tests.
+```
+
+## Critical files
+
+- [scripts/match_payments.py](scripts/match_payments.py) — Python reconcile (canonical)
+- [go/internal/domain/reconcile/reconcile.go](go/internal/domain/reconcile/reconcile.go) — Go reconcile (mirrors Python)
+- [tests/test_reconcile_exceptions.py](tests/test_reconcile_exceptions.py) — rewrite `test_proportional_underpayment` + add Matyáš test
+- [go/internal/domain/reconcile/reconcile_test.go](go/internal/domain/reconcile/reconcile_test.go) — add Go tests
+- [go/tests/parity/reconcile/reconcile_parity_test.go](go/tests/parity/reconcile/reconcile_parity_test.go) — add parity fixture
+- [CHANGELOG.md](CHANGELOG.md) — top entry
+
+## Verification
+
+1. `make test` — Python unit tests including the rewritten + new fill-first tests.
+2. `cd go && go test ./internal/domain/reconcile/... ./tests/parity/reconcile/...` — Go unit + parity tests.
+3. `make web` → load `/adults` or `/juniors` (whichever lists Matyáš Thér) → his 2026-02 row should be fully paid (no shortfall), 2026-03 fully paid, no leftover credit.
+4. Spot-check one other multi-month-purpose member to make sure fully-covered cases still look right.
+
+## Branch & MR (per CLAUDE.md)
+
+1. `git checkout -b fix/fill-first-multi-month-allocation`
+2. Apply edits + tests + CHANGELOG entry.
+3. `make test && (cd go && go test ./...)` — both green.
+4. Commit: `fix(reconcile): fill earliest month deficit first in multi-month allocations` with `Co-Authored-By` trailer.
+5. `git push -u origin fix/fill-first-multi-month-allocation`
+6. `tea pr create --title "fix(reconcile): fill earliest month deficit first" --description "<body>" --base main --head fix/fill-first-multi-month-allocation`
+7. Print MR URL. Do not merge from CLI.

go/cmd/fuj/main.go

@@ -1,12 +1,20 @@
 package main
 
 import (
+	"context"
 	"flag"
 	"fmt"
 	"fuj-management/go/internal/config"
+	"fuj-management/go/internal/io/fio"
+	"fuj-management/go/internal/io/sheets"
 	"fuj-management/go/internal/logging"
+	"fuj-management/go/internal/services/banksync"
+	"fuj-management/go/internal/services/membership"
 	"fuj-management/go/internal/web"
+	"io"
+	"log/slog"
 	"os"
+	"time"
 )
 
 // Injected at build time via -ldflags "-X main.version=... -X main.commit=... -X main.buildDate=..."
@@ -22,6 +30,9 @@ func main() {
 		os.Exit(2)
 	}
 
+	// Honour LOG_LEVEL for slog calls in any package (e.g. internal/io/fio debug logs).
+	slog.SetDefault(logging.New(os.Getenv("LOG_LEVEL")))
+
 	cmd, args := os.Args[1], os.Args[2:]
 
 	switch cmd {
@@ -29,9 +40,14 @@ func main() {
 		serverCmd(args)
 	case "version":
 		versionCmd()
-	case "fees", "reconcile", "sync", "infer":
-		fmt.Fprintf(os.Stderr, "fuj %s: not implemented yet (lands in M2/M4)\n", cmd)
-		os.Exit(2)
+	case "fees":
+		feesCmd(args)
+	case "reconcile":
+		reconcileCmd(args)
+	case "sync":
+		syncCmd(args)
+	case "infer":
+		inferCmd(args)
 	case "-h", "--help", "help":
 		usage()
 	default:
@@ -58,27 +74,203 @@ func serverCmd(args []string) {
 		cfg.ServerAddr = *addr
 	}
 
+	ctx := context.Background()
 	logger := logging.New(cfg.LogLevel)
+
+	sources, err := membership.NewSources(ctx, cfg)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "fuj server: init sources: %v\n", err)
+		os.Exit(1)
+	}
+
+	sheetsCli, err := sheets.New(ctx, cfg.CredentialsPath, cfg.DriveTimeout)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "fuj server: sheets client for sync: %v\n", err)
+		os.Exit(1)
+	}
+	fioCli := fio.New(cfg.FioAPIToken, config.IBANAccountNum(cfg.BankAccount), nil)
+
+	actions := web.ActionHandlers{
+		BankSync: func(ctx context.Context, out io.Writer) error {
+			yr := time.Now().Year()
+			from := time.Date(yr, 1, 1, 0, 0, 0, 0, time.UTC)
+			to := time.Date(yr, 12, 31, 23, 59, 59, 0, time.UTC)
+
+			fmt.Fprintln(out, "=== Sync Fio Transactions ===")
+			n, err := banksync.SyncToSheets(ctx, config.PaymentsSheetID, fioCli, sheetsCli,
+				banksync.SyncOpts{From: from, To: to, Sort: true})
+			if err != nil {
+				return fmt.Errorf("sync: %w", err)
+			}
+			fmt.Fprintf(out, "Synced %d new transaction(s).\n\n", n)
+
+			fmt.Fprintln(out, "=== Infer Payments ===")
+			n, err = banksync.InferPayments(ctx, config.PaymentsSheetID, sheetsCli, sources, banksync.InferOpts{})
+			if err != nil {
+				return fmt.Errorf("infer: %w", err)
+			}
+			fmt.Fprintf(out, "Inferred %d row(s).\n", n)
+			return nil
+		},
+	}
+
 	build := web.BuildInfo{Version: version, Commit: commit, BuildDate: buildDate}
 
-	if err := web.Run(logger, cfg.ServerAddr, build); err != nil {
+	if err := web.Run(logger, cfg.ServerAddr, build, sources, cfg, actions); err != nil {
 		fmt.Fprintln(os.Stderr, err)
 		os.Exit(1)
 	}
 }
 
+func feesCmd(args []string) {
+	fs := flag.NewFlagSet("fees", flag.ExitOnError)
+	fs.Usage = func() {
+		fmt.Fprintln(os.Stderr, "usage: fuj fees")
+	}
+	if err := fs.Parse(args); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+	}
+
+	ctx := context.Background()
+	cfg := config.Load()
+	sources, err := membership.NewSources(ctx, cfg)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "fuj fees: %v\n", err)
+		os.Exit(1)
+	}
+	if err := membership.FeesReport(ctx, sources, os.Stdout); err != nil {
+		fmt.Fprintf(os.Stderr, "fuj fees: %v\n", err)
+		os.Exit(1)
+	}
+}
+
+func reconcileCmd(args []string) {
+	fs := flag.NewFlagSet("reconcile", flag.ExitOnError)
+	fs.Usage = func() {
+		fmt.Fprintln(os.Stderr, "usage: fuj reconcile")
+	}
+	if err := fs.Parse(args); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+	}
+
+	ctx := context.Background()
+	cfg := config.Load()
+	sources, err := membership.NewSources(ctx, cfg)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "fuj reconcile: %v\n", err)
+		os.Exit(1)
+	}
+	if err := membership.ReconcileReport(ctx, sources, time.Now().Year(), os.Stdout); err != nil {
+		fmt.Fprintf(os.Stderr, "fuj reconcile: %v\n", err)
+		os.Exit(1)
+	}
+}
+
 func versionCmd() {
 	fmt.Printf("fuj %s (%s) built %s\n", version, commit, buildDate)
 }
 
+func syncCmd(args []string) {
+	fs := flag.NewFlagSet("sync", flag.ExitOnError)
+	days := fs.Int("days", 30, "look-back window in days (ignored when --from/--to are set)")
+	fromStr := fs.String("from", "", "start date YYYY-MM-DD")
+	toStr := fs.String("to", "", "end date YYYY-MM-DD")
+	sort := fs.Bool("sort", true, "sort sheet by date after appending")
+	dryRun := fs.Bool("dry-run", false, "print planned writes without modifying the sheet")
+	printFioTable := fs.Bool("print-fio-table", false, "with --dry-run: print aligned table of every Fio transaction with NEW/DUP status")
+	fs.Usage = func() {
+		fmt.Fprintln(os.Stderr, "usage: fuj sync [--days N] [--from YYYY-MM-DD --to YYYY-MM-DD] [--sort] [--dry-run] [--print-fio-table]")
+		fs.PrintDefaults()
+	}
+	if err := fs.Parse(args); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+	}
+
+	ctx := context.Background()
+	cfg := config.Load()
+
+	sheetsCli, err := sheets.New(ctx, cfg.CredentialsPath, cfg.DriveTimeout)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "fuj sync: sheets client: %v\n", err)
+		os.Exit(1)
+	}
+	fioCli := fio.New(cfg.FioAPIToken, config.IBANAccountNum(cfg.BankAccount), nil)
+
+	opts := banksync.SyncOpts{Days: *days, Sort: *sort, DryRun: *dryRun, PrintFioTable: *printFioTable}
+	if *fromStr != "" && *toStr != "" {
+		opts.From, err = time.Parse("2006-01-02", *fromStr)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "fuj sync: invalid --from: %v\n", err)
+			os.Exit(2)
+		}
+		opts.To, err = time.Parse("2006-01-02", *toStr)
+		if err != nil {
+			fmt.Fprintf(os.Stderr, "fuj sync: invalid --to: %v\n", err)
+			os.Exit(2)
+		}
+	}
+
+	n, err := banksync.SyncToSheets(ctx, config.PaymentsSheetID, fioCli, sheetsCli, opts)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "fuj sync: %v\n", err)
+		os.Exit(1)
+	}
+	if *dryRun {
+		fmt.Printf("Dry run: would sync %d new transaction(s).\n", n)
+	} else {
+		fmt.Printf("Synced %d new transaction(s).\n", n)
+	}
+}
+
+func inferCmd(args []string) {
+	fs := flag.NewFlagSet("infer", flag.ExitOnError)
+	dryRun := fs.Bool("dry-run", false, "print planned updates without writing to the sheet")
+	fs.Usage = func() {
+		fmt.Fprintln(os.Stderr, "usage: fuj infer [--dry-run]")
+		fs.PrintDefaults()
+	}
+	if err := fs.Parse(args); err != nil {
+		fmt.Fprintln(os.Stderr, err)
+		os.Exit(2)
+	}
+
+	ctx := context.Background()
+	cfg := config.Load()
+
+	sheetsCli, err := sheets.New(ctx, cfg.CredentialsPath, cfg.DriveTimeout)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "fuj infer: sheets client: %v\n", err)
+		os.Exit(1)
+	}
+	sources, err := membership.NewSources(ctx, cfg)
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "fuj infer: sources: %v\n", err)
+		os.Exit(1)
+	}
+
+	n, err := banksync.InferPayments(ctx, config.PaymentsSheetID, sheetsCli, sources, banksync.InferOpts{DryRun: *dryRun})
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "fuj infer: %v\n", err)
+		os.Exit(1)
+	}
+	if *dryRun {
+		fmt.Printf("Dry run: would update %d row(s).\n", n)
+	} else {
+		fmt.Printf("Updated %d row(s).\n", n)
+	}
+}
+
 func usage() {
 	fmt.Fprintln(os.Stderr, `usage: fuj <command> [flags]
 
 Commands:
   server      Start HTTP server (default :8080)
   version     Print version information
-  fees        Calculate monthly fees  [M2]
-  reconcile   Show balance report     [M2]
-  sync        Sync Fio transactions   [M4]
-  infer       Infer payment details   [M4]`)
+  fees        Calculate monthly fees
+  reconcile   Show balance report
+  sync        Sync Fio transactions to payments sheet
+  infer       Infer payment details in payments sheet`)
 }

go/cmd/parity/main.go

@@ -0,0 +1,133 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"net/http"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
+)
+
+// /api/version is intentionally excluded — it returns each binary's own build
+// identity (tag/commit/build_date), which differs by design between independently
+// built backends. Pass -route /api/version to inspect it manually.
+var allRoutes = []string{"/api/adults", "/api/juniors", "/api/payments"}
+
+// defaultAllowlist holds dotted key paths to strip before diffing.
+// render_time.total is forward-compatible insurance: today it lives in the Jinja
+// template context only (app.py inject_render_time) and is logged via
+// middleware/timer.go on the Go side, so it isn't in any JSON response. If either
+// side ever surfaces it under a render_time envelope, the scrubber handles it.
+var defaultAllowlist = []string{"render_time.total"}
+
+func main() {
+	pyURL := flag.String("py", "http://localhost:5001", "Python backend base URL")
+	goURL := flag.String("go", "http://localhost:8080", "Go backend base URL")
+	route := flag.String("route", "", "single route to diff, e.g. /api/adults (default: all)")
+	timeout := flag.Duration("timeout", 30*time.Second, "per-request HTTP timeout")
+	flag.Parse()
+
+	client := &http.Client{Timeout: *timeout}
+
+	targets := allRoutes
+	if *route != "" {
+		targets = []string{*route}
+	}
+
+	matched, diffs, errs := 0, 0, 0
+
+	for _, r := range targets {
+		pyMap, err1 := fetch(client, *pyURL+r)
+		goMap, err2 := fetch(client, *goURL+r)
+
+		if err1 != nil || err2 != nil {
+			fmt.Printf("=== %s ===\n", r)
+			if err1 != nil {
+				fmt.Printf("ERROR (py): %v\n", err1)
+			}
+			if err2 != nil {
+				fmt.Printf("ERROR (go): %v\n", err2)
+			}
+			fmt.Println()
+			errs++
+			continue
+		}
+
+		scrub(pyMap, defaultAllowlist)
+		scrub(goMap, defaultAllowlist)
+
+		diff := cmp.Diff(pyMap, goMap, cmpopts.EquateEmpty())
+		if diff == "" {
+			fmt.Printf("=== %s ===\nOK\n\n", r)
+			matched++
+		} else {
+			fmt.Printf("=== %s ===\n%s\n", r, diff)
+			diffs++
+		}
+	}
+
+	total := len(targets)
+	fmt.Printf("parity: %d/%d routes match", matched, total)
+	if diffs > 0 {
+		fmt.Printf(", %d diff", diffs)
+		if diffs > 1 {
+			fmt.Print("s")
+		}
+	}
+	if errs > 0 {
+		fmt.Printf(", %d error", errs)
+		if errs > 1 {
+			fmt.Print("s")
+		}
+	}
+	fmt.Println()
+
+	if errs > 0 {
+		os.Exit(2)
+	}
+	if diffs > 0 {
+		os.Exit(1)
+	}
+}
+
+func fetch(client *http.Client, url string) (map[string]any, error) {
+	resp, err := client.Get(url) //nolint:noctx
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, fmt.Errorf("read body: %w", err)
+	}
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("HTTP %d: %s", resp.StatusCode, strings.TrimSpace(string(body)))
+	}
+	var m map[string]any
+	if err := json.Unmarshal(body, &m); err != nil {
+		return nil, fmt.Errorf("decode JSON: %w", err)
+	}
+	return m, nil
+}
+
+// scrub removes keys from m whose dotted paths appear in paths.
+// A bare segment (no dot) deletes a top-level key.
+// A two-segment path "parent.child" deletes child from m["parent"] if it is a map.
+func scrub(m map[string]any, paths []string) {
+	for _, path := range paths {
+		parts := strings.SplitN(path, ".", 2)
+		if len(parts) == 1 {
+			delete(m, parts[0])
+		} else {
+			if child, ok := m[parts[0]].(map[string]any); ok {
+				delete(child, parts[1])
+			}
+		}
+	}
+}

go/cmd/parity/scrub_test.go

@@ -0,0 +1,57 @@
+package main
+
+import "testing"
+
+func TestScrubTopLevel(t *testing.T) {
+	m := map[string]any{
+		"build_meta": map[string]any{"tag": "v1"},
+		"other":      "keep",
+	}
+	scrub(m, []string{"build_meta"})
+	if _, ok := m["build_meta"]; ok {
+		t.Error("expected build_meta to be removed")
+	}
+	if m["other"] != "keep" {
+		t.Error("expected other to be preserved")
+	}
+}
+
+func TestScrubNested(t *testing.T) {
+	m := map[string]any{
+		"render_time": map[string]any{
+			"total":     "0.123",
+			"breakdown": "fetch:0.1s",
+		},
+		"other": "keep",
+	}
+	scrub(m, []string{"render_time.total"})
+	rt, ok := m["render_time"].(map[string]any)
+	if !ok {
+		t.Fatal("render_time should still be present")
+	}
+	if _, ok := rt["total"]; ok {
+		t.Error("expected render_time.total to be removed")
+	}
+	if rt["breakdown"] != "fetch:0.1s" {
+		t.Error("expected render_time.breakdown to be preserved")
+	}
+	if m["other"] != "keep" {
+		t.Error("expected other to be preserved")
+	}
+}
+
+func TestScrubMissingPath(t *testing.T) {
+	m := map[string]any{"foo": "bar"}
+	scrub(m, []string{"nonexistent", "render_time.total"})
+	if m["foo"] != "bar" {
+		t.Error("expected foo to be preserved")
+	}
+}
+
+func TestScrubNestedParentNotMap(t *testing.T) {
+	m := map[string]any{"render_time": "not-a-map"}
+	scrub(m, []string{"render_time.total"})
+	if m["render_time"] != "not-a-map" {
+		t.Error("expected render_time to be unchanged when it is not a map")
+	}
+}

go/go.mod

@@ -2,4 +2,40 @@ module fuj-management/go
 
 go 1.26.1
 
-require golang.org/x/text v0.36.0
+require (
+	github.com/google/go-cmp v0.7.0
+	github.com/invopop/jsonschema v0.14.0
+	github.com/skip2/go-qrcode v0.0.0-20200617195104-da1b6568686e
+	golang.org/x/net v0.53.0
+	golang.org/x/text v0.36.0
+	google.golang.org/api v0.278.0
+)
+
+require (
+	cloud.google.com/go/auth v0.20.0 // indirect
+	cloud.google.com/go/auth/oauth2adapt v0.2.8 // indirect
+	cloud.google.com/go/compute/metadata v0.9.0 // indirect
+	github.com/bahlo/generic-list-go v0.2.0 // indirect
+	github.com/buger/jsonparser v1.1.2 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
+	github.com/felixge/httpsnoop v1.0.4 // indirect
+	github.com/go-logr/logr v1.4.3 // indirect
+	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/google/s2a-go v0.1.9 // indirect
+	github.com/google/uuid v1.6.0 // indirect
+	github.com/googleapis/enterprise-certificate-proxy v0.3.15 // indirect
+	github.com/googleapis/gax-go/v2 v2.22.0 // indirect
+	github.com/pb33f/ordered-map/v2 v2.3.1 // indirect
+	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
+	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.67.0 // indirect
+	go.opentelemetry.io/otel v1.43.0 // indirect
+	go.opentelemetry.io/otel/metric v1.43.0 // indirect
+	go.opentelemetry.io/otel/trace v1.43.0 // indirect
+	go.yaml.in/yaml/v4 v4.0.0-rc.2 // indirect
+	golang.org/x/crypto v0.50.0 // indirect
+	golang.org/x/oauth2 v0.36.0 // indirect
+	golang.org/x/sys v0.43.0 // indirect
+	google.golang.org/genproto/googleapis/rpc v0.0.0-20260427160629-7cedc36a6bc4 // indirect
+	google.golang.org/grpc v1.80.0 // indirect
+	google.golang.org/protobuf v1.36.11 // indirect
+)

go/go.sum

@@ -1,2 +1,87 @@
+cloud.google.com/go/auth v0.20.0 h1:kXTssoVb4azsVDoUiF8KvxAqrsQcQtB53DcSgta74CA=
+cloud.google.com/go/auth v0.20.0/go.mod h1:942/yi/itH1SsmpyrbnTMDgGfdy2BUqIKyd0cyYLc5Q=
+cloud.google.com/go/auth/oauth2adapt v0.2.8 h1:keo8NaayQZ6wimpNSmW5OPc283g65QNIiLpZnkHRbnc=
+cloud.google.com/go/auth/oauth2adapt v0.2.8/go.mod h1:XQ9y31RkqZCcwJWNSx2Xvric3RrU88hAYYbjDWYDL+c=
+cloud.google.com/go/compute/metadata v0.9.0 h1:pDUj4QMoPejqq20dK0Pg2N4yG9zIkYGdBtwLoEkH9Zs=
+cloud.google.com/go/compute/metadata v0.9.0/go.mod h1:E0bWwX5wTnLPedCKqk3pJmVgCBSM6qQI1yTBdEb3C10=
+github.com/bahlo/generic-list-go v0.2.0 h1:5sz/EEAK+ls5wF+NeqDpk5+iNdMDXrh3z3nPnH1Wvgk=
+github.com/bahlo/generic-list-go v0.2.0/go.mod h1:2KvAjgMlE5NNynlg/5iLrrCCZ2+5xWbdbCW3pNTGyYg=
+github.com/buger/jsonparser v1.1.2 h1:frqHqw7otoVbk5M8LlE/L7HTnIq2v9RX6EJ48i9AxJk=
+github.com/buger/jsonparser v1.1.2/go.mod h1:6RYKKt7H4d4+iWqouImQ9R2FZql3VbhNgx27UK13J/0=
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+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
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+go.opentelemetry.io/otel/trace v1.43.0 h1:BkNrHpup+4k4w+ZZ86CZoHHEkohws8AY+WTX09nk+3A=
+go.opentelemetry.io/otel/trace v1.43.0/go.mod h1:/QJhyVBUUswCphDVxq+8mld+AvhXZLhe+8WVFxiFff0=
+go.yaml.in/yaml/v4 v4.0.0-rc.2 h1:/FrI8D64VSr4HtGIlUtlFMGsm7H7pWTbj6vOLVZcA6s=
+go.yaml.in/yaml/v4 v4.0.0-rc.2/go.mod h1:aZqd9kCMsGL7AuUv/m/PvWLdg5sjJsZ4oHDEnfPPfY0=
+golang.org/x/crypto v0.50.0 h1:zO47/JPrL6vsNkINmLoo/PH1gcxpls50DNogFvB5ZGI=
+golang.org/x/crypto v0.50.0/go.mod h1:3muZ7vA7PBCE6xgPX7nkzzjiUq87kRItoJQM1Yo8S+Q=
+golang.org/x/net v0.53.0 h1:d+qAbo5L0orcWAr0a9JweQpjXF19LMXJE8Ey7hwOdUA=
+golang.org/x/net v0.53.0/go.mod h1:JvMuJH7rrdiCfbeHoo3fCQU24Lf5JJwT9W3sJFulfgs=
+golang.org/x/oauth2 v0.36.0 h1:peZ/1z27fi9hUOFCAZaHyrpWG5lwe0RJEEEeH0ThlIs=
+golang.org/x/oauth2 v0.36.0/go.mod h1:YDBUJMTkDnJS+A4BP4eZBjCqtokkg1hODuPjwiGPO7Q=
+golang.org/x/sync v0.20.0 h1:e0PTpb7pjO8GAtTs2dQ6jYa5BWYlMuX047Dco/pItO4=
+golang.org/x/sync v0.20.0/go.mod h1:9xrNwdLfx4jkKbNva9FpL6vEN7evnE43NNNJQ2LF3+0=
+golang.org/x/sys v0.43.0 h1:Rlag2XtaFTxp19wS8MXlJwTvoh8ArU6ezoyFsMyCTNI=
+golang.org/x/sys v0.43.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
 golang.org/x/text v0.36.0 h1:JfKh3XmcRPqZPKevfXVpI1wXPTqbkE5f7JA92a55Yxg=
 golang.org/x/text v0.36.0/go.mod h1:NIdBknypM8iqVmPiuco0Dh6P5Jcdk8lJL0CUebqK164=
+gonum.org/v1/gonum v0.17.0 h1:VbpOemQlsSMrYmn7T2OUvQ4dqxQXU+ouZFQsZOx50z4=
+gonum.org/v1/gonum v0.17.0/go.mod h1:El3tOrEuMpv2UdMrbNlKEh9vd86bmQ6vqIcDwxEOc1E=
+google.golang.org/api v0.278.0 h1:W7jiRvRi53VYFfZ/HoZjQBtJk7gOFbHD8ot1RzVZU6E=
+google.golang.org/api v0.278.0/go.mod h1:B9TqLBwJqVjp1mtt7WeoQwWRwvu/400y5lETOql+giQ=
+google.golang.org/genproto v0.0.0-20260319201613-d00831a3d3e7 h1:XzmzkmB14QhVhgnawEVsOn6OFsnpyxNPRY9QV01dNB0=
+google.golang.org/genproto v0.0.0-20260319201613-d00831a3d3e7/go.mod h1:L43LFes82YgSonw6iTXTxXUX1OlULt4AQtkik4ULL/I=
+google.golang.org/genproto/googleapis/api v0.0.0-20260319201613-d00831a3d3e7 h1:41r6JMbpzBMen0R/4TZeeAmGXSJC7DftGINUodzTkPI=
+google.golang.org/genproto/googleapis/api v0.0.0-20260319201613-d00831a3d3e7/go.mod h1:EIQZ5bFCfRQDV4MhRle7+OgjNtZ6P1PiZBgAKuxXu/Y=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20260427160629-7cedc36a6bc4 h1:tEkOQcXgF6dH1G+MVKZrfpYvozGrzb91k6ha7jireSM=
+google.golang.org/genproto/googleapis/rpc v0.0.0-20260427160629-7cedc36a6bc4/go.mod h1:4Hqkh8ycfw05ld/3BWL7rJOSfebL2Q+DVDeRgYgxUU8=
+google.golang.org/grpc v1.80.0 h1:Xr6m2WmWZLETvUNvIUmeD5OAagMw3FiKmMlTdViWsHM=
+google.golang.org/grpc v1.80.0/go.mod h1:ho/dLnxwi3EDJA4Zghp7k2Ec1+c2jqup0bFkw07bwF4=
+google.golang.org/protobuf v1.36.11 h1:fV6ZwhNocDyBLK0dj+fg8ektcVegBBuEolpbTQyBNVE=
+google.golang.org/protobuf v1.36.11/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

go/internal/config/config.go

@@ -3,6 +3,7 @@ package config
 import (
 	"os"
 	"strconv"
+	"strings"
 	"time"
 )
 
@@ -10,16 +11,34 @@ import (
 const (
 	AttendanceSheetID = "1E2e_gT_K5AwSRCDLDTa2UetZTkHmBOcz0kFbBUNUNBA"
 	PaymentsSheetID   = "1Om0YPoDVCH5cV8BrNz5LG5eR5MMU05ypQC7UMN1xn_Y"
-	JuniorSheetGID    = "1213318614"
+
+	// Both attendance tabs live in the same Google Spreadsheet (AttendanceSheetID).
+	// The original adult and junior attendance data lives in separate source spreadsheets,
+	// but is collected into this one sheet via IMPORTRANGE — one tab per group.
+	// Tabs are identified by the gid= query param in the CSV export URL.
+	AttendanceAdultSheetGID = "0"          // gid=0 — adult practices tab (IMPORTRANGE'd)
+	JuniorSheetGID          = "1213318614" // gid=1213318614 — junior practices tab (IMPORTRANGE'd)
 )
 
+// CacheSheetMap mirrors scripts/config.py CACHE_SHEET_MAP.
+// Maps a cache key to the Google Sheet ID whose Drive modifiedTime gates it.
+// Both attendance keys map to the same spreadsheet — different tabs, one Drive file.
+var CacheSheetMap = map[string]string{
+	"attendance_regular":    AttendanceSheetID,
+	"attendance_juniors":    AttendanceSheetID,
+	"exceptions_dict":       PaymentsSheetID,
+	"payments_transactions": PaymentsSheetID,
+}
+
 // Config holds all runtime configuration loaded from environment variables.
 // Mirrors scripts/config.py.
 type Config struct {
 	CredentialsPath  string
 	BankAccount      string
+	CacheDir         string
 	CacheTTL         time.Duration
 	CacheAPICheckTTL time.Duration
+	DriveTimeout     time.Duration
 	LogLevel         string
 	FioAPIToken      string
 	ServerAddr       string
@@ -31,14 +50,32 @@ func Load() Config {
 	return Config{
 		CredentialsPath:  env("CREDENTIALS_PATH", ".secret/fuj-management-bot-credentials.json"),
 		BankAccount:      env("BANK_ACCOUNT", "CZ8520100000002800359168"),
+		CacheDir:         env("CACHE_DIR", "tmp/go"),
 		CacheTTL:         envDuration("CACHE_TTL_SECONDS", 300),
 		CacheAPICheckTTL: envDuration("CACHE_API_CHECK_TTL_SECONDS", 300),
+		DriveTimeout:     envDuration("DRIVE_TIMEOUT_SECONDS", 10),
 		LogLevel:         env("LOG_LEVEL", "INFO"),
 		FioAPIToken:      env("FIO_API_TOKEN", ""),
 		ServerAddr:       env("SERVER_ADDR", ":8080"),
 	}
 }
 
+// IBANAccountNum extracts the bare account number from a Czech IBAN.
+// "CZ8520100000002800359168" → "2800359168"
+// Structure: CZ(2 check)(4 bank code)(16 zero-padded account).
+func IBANAccountNum(iban string) string {
+	s := strings.ReplaceAll(iban, " ", "")
+	if len(s) < 8 {
+		return iban
+	}
+	raw := s[8:] // 16-digit zero-padded account portion
+	n := strings.TrimLeft(raw, "0")
+	if n == "" {
+		return "0"
+	}
+	return n
+}
+
 func env(key, fallback string) string {
 	if v := os.Getenv(key); v != "" {
 		return v

go/internal/domain/matching/doc.go

@@ -0,0 +1,2 @@
+// Package matching ports name/member matching from scripts/match_payments.py.
+package matching

go/internal/domain/matching/format_date.go

@@ -0,0 +1,41 @@
+package matching
+
+import (
+	"fmt"
+	"strings"
+	"time"
+)
+
+var sheetsEpoch = time.Date(1899, 12, 30, 0, 0, 0, 0, time.UTC)
+
+// FormatDate normalizes a date value from Google Sheets.
+//
+// Accepts nil, empty string, int/float64 Sheets serial days since 1899-12-30,
+// a pre-formatted "YYYY-MM-DD" string (returned as-is), or any other value
+// (returned as fmt.Sprint(v).TrimSpace). Never returns an error.
+//
+// Ports scripts/match_payments.py format_date.
+func FormatDate(val any) string {
+	if val == nil {
+		return ""
+	}
+	switch v := val.(type) {
+	case int:
+		return sheetsEpoch.Add(time.Duration(float64(v) * 24 * float64(time.Hour))).Format("2006-01-02")
+	case int64:
+		return sheetsEpoch.Add(time.Duration(float64(v) * 24 * float64(time.Hour))).Format("2006-01-02")
+	case float64:
+		return sheetsEpoch.Add(time.Duration(v * 24 * float64(time.Hour))).Format("2006-01-02")
+	case string:
+		s := strings.TrimSpace(v)
+		if s == "" {
+			return ""
+		}
+		if len(s) == 10 && s[4] == '-' && s[7] == '-' {
+			return s
+		}
+		return s
+	default:
+		return strings.TrimSpace(fmt.Sprint(v))
+	}
+}

go/internal/domain/matching/format_date_test.go

@@ -0,0 +1,49 @@
+package matching
+
+// Expected values verified against scripts/match_payments.py on 2026-05-06:
+//
+//	PYTHONPATH=scripts:. python3 -c '
+//	from match_payments import format_date
+//	for v in [None, "", 44197, 44197.5, "2026-04-15", "garbage", "  2026-04-15  "]:
+//	    print(repr(format_date(v)))
+//	'
+//
+// Output:
+//
+//	''
+//	''
+//	'2021-01-01'
+//	'2021-01-01'
+//	'2026-04-15'
+//	'garbage'
+//	'2026-04-15'
+
+import "testing"
+
+func TestFormatDate(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name  string
+		input any
+		want  string
+	}{
+		{name: "nil", input: nil, want: ""},
+		{name: "empty string", input: "", want: ""},
+		{name: "serial int", input: int(44197), want: "2021-01-01"},
+		{name: "serial float fractional", input: float64(44197.5), want: "2021-01-01"},
+		{name: "already formatted", input: "2026-04-15", want: "2026-04-15"},
+		{name: "garbage string", input: "garbage", want: "garbage"},
+		{name: "padded date string trimmed", input: "  2026-04-15  ", want: "2026-04-15"},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := FormatDate(tc.input)
+			if got != tc.want {
+				t.Errorf("FormatDate(%v) = %q, want %q", tc.input, got, tc.want)
+			}
+		})
+	}
+}

go/internal/domain/matching/infer.go

@@ -0,0 +1,89 @@
+package matching
+
+import (
+	"fmt"
+	"fuj-management/go/internal/domain/czech"
+	"time"
+)
+
+// Transaction is the subset of a payment row used by InferTransactionDetails.
+// Date accepts string ("YYYY-MM-DD"), float64 (Sheets serial), or int — matching
+// the heterogeneous types returned by the Sheets API and the FIO scraper.
+type Transaction struct {
+	Sender  string
+	Message string
+	UserID  string
+	Date    any
+}
+
+// InferredDetails is the result of InferTransactionDetails.
+type InferredDetails struct {
+	Members    []Match
+	Months     []string
+	SearchText string
+}
+
+// InferTransactionDetails infers which member(s) and month(s) a transaction belongs to.
+//
+// Search text for member matching: sender + message + user_id.
+// Month search text: message + user_id only (sender excluded, matching Python).
+// Fallback 1: if no members found, retry match on sender alone.
+// Fallback 2: if no months found, derive from tx.Date (Sheets serial or YYYY-MM-DD).
+//
+// defaultYear seeds czech.ParseMonthReferences (Python defaulted to the current year;
+// callers should pass time.Now().Year() or a fixed year for deterministic tests).
+//
+// Ports scripts/match_payments.py infer_transaction_details.
+func InferTransactionDetails(tx Transaction, memberNames []string, defaultYear int) InferredDetails {
+	searchText := fmt.Sprintf("%s %s %s", tx.Sender, tx.Message, tx.UserID)
+
+	members := MatchMembers(searchText, memberNames)
+	months := czech.ParseMonthReferences(tx.Message+" "+tx.UserID, defaultYear)
+
+	if len(members) == 0 {
+		members = MatchMembers(tx.Sender, memberNames)
+	}
+
+	if len(months) == 0 && tx.Date != nil && tx.Date != "" {
+		if ym := inferMonthFromDate(tx.Date); ym != "" {
+			months = []string{ym}
+		}
+	}
+
+	if months == nil {
+		months = []string{}
+	}
+
+	return InferredDetails{
+		Members:    members,
+		Months:     months,
+		SearchText: searchText,
+	}
+}
+
+// inferMonthFromDate converts a date value to "YYYY-MM" for the month fallback.
+// Returns "" on any error, matching Python's bare except pass.
+func inferMonthFromDate(val any) string {
+	switch v := val.(type) {
+	case int:
+		dt := sheetsEpoch.Add(time.Duration(float64(v) * 24 * float64(time.Hour)))
+		return dt.Format("2006-01")
+	case int64:
+		dt := sheetsEpoch.Add(time.Duration(float64(v) * 24 * float64(time.Hour)))
+		return dt.Format("2006-01")
+	case float64:
+		dt := sheetsEpoch.Add(time.Duration(v * 24 * float64(time.Hour)))
+		return dt.Format("2006-01")
+	case string:
+		if v == "" {
+			return ""
+		}
+		dt, err := time.Parse("2006-01-02", v)
+		if err != nil {
+			return ""
+		}
+		return dt.Format("2006-01")
+	default:
+		return ""
+	}
+}

go/internal/domain/matching/infer_test.go

@@ -0,0 +1,108 @@
+package matching
+
+// Expected values verified against scripts/match_payments.py on 2026-05-06:
+//
+//	PYTHONPATH=scripts:. python3 << 'EOF'
+//	from match_payments import infer_transaction_details
+//	MEMBERS = ["Tomáš Němeček (Tov)", "Jana Nováková"]
+//	cases = [
+//	    ({"sender":"Tomas Nemecek","message":"clenske 04/2026","user_id":"","date":"2026-04-15"}, "full match"),
+//	    ({"sender":"Tomas Nemecek","message":"","user_id":"","date":"2026-04-15"}, "sender fallback month"),
+//	    ({"sender":"Jana Novakova","message":"","user_id":"","date":44197}, "serial int date"),
+//	    ({"sender":"neznamy","message":"","user_id":"","date":""}, "no match"),
+//	    ({"sender":"Tomas Nemecek","message":"","user_id":"","date":44197.5}, "serial float date"),
+//	]
+//	for tx, label in cases:
+//	    r = infer_transaction_details(tx, MEMBERS)
+//	    print(label + ": members=" + repr(r["members"]) + " months=" + repr(r["months"]) + " search_text=" + repr(r["search_text"]))
+//	EOF
+//
+// Output:
+//
+//	full match: members=[('Tomáš Němeček (Tov)', 'auto')] months=['2026-04'] search_text='Tomas Nemecek clenske 04/2026 '
+//	sender fallback month: members=[('Tomáš Němeček (Tov)', 'auto')] months=['2026-04'] search_text='Tomas Nemecek  '
+//	serial int date: members=[('Jana Nováková', 'auto')] months=['2021-01'] search_text='Jana Novakova  '
+//	no match: members=[] months=[] search_text='neznamy  '
+//	serial float date: members=[('Tomáš Němeček (Tov)', 'auto')] months=['2021-01'] search_text='Tomas Nemecek  '
+
+import (
+	"reflect"
+	"testing"
+)
+
+var inferMembers = []string{"Tomáš Němeček (Tov)", "Jana Nováková"}
+
+func TestInferTransactionDetails(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name           string
+		tx             Transaction
+		defaultYear    int
+		wantMembers    []Match
+		wantMonths     []string
+		wantSearchText string
+	}{
+		{
+			name:        "full match — members and months from search text",
+			tx:          Transaction{Sender: "Tomas Nemecek", Message: "clenske 04/2026", UserID: "", Date: "2026-04-15"},
+			defaultYear: 2026,
+			wantMembers: []Match{{Name: "Tomáš Němeček (Tov)", Confidence: ConfidenceAuto}},
+			wantMonths:  []string{"2026-04"},
+			// Python: sender + " " + message + " " + user_id (no trim)
+			wantSearchText: "Tomas Nemecek clenske 04/2026 ",
+		},
+		{
+			// months not in message → fall back to date string
+			name:           "months fall back to date string",
+			tx:             Transaction{Sender: "Tomas Nemecek", Message: "", UserID: "", Date: "2026-04-15"},
+			defaultYear:    2026,
+			wantMembers:    []Match{{Name: "Tomáš Němeček (Tov)", Confidence: ConfidenceAuto}},
+			wantMonths:     []string{"2026-04"},
+			wantSearchText: "Tomas Nemecek  ",
+		},
+		{
+			// months fall back to Sheets serial int date
+			name:           "months fall back to serial int date",
+			tx:             Transaction{Sender: "Jana Novakova", Message: "", UserID: "", Date: int(44197)},
+			defaultYear:    2026,
+			wantMembers:    []Match{{Name: "Jana Nováková", Confidence: ConfidenceAuto}},
+			wantMonths:     []string{"2021-01"},
+			wantSearchText: "Jana Novakova  ",
+		},
+		{
+			// months fall back to Sheets serial float64 date
+			name:           "months fall back to serial float date",
+			tx:             Transaction{Sender: "Tomas Nemecek", Message: "", UserID: "", Date: float64(44197.5)},
+			defaultYear:    2026,
+			wantMembers:    []Match{{Name: "Tomáš Němeček (Tov)", Confidence: ConfidenceAuto}},
+			wantMonths:     []string{"2021-01"},
+			wantSearchText: "Tomas Nemecek  ",
+		},
+		{
+			name:           "no match — both slices empty not nil",
+			tx:             Transaction{Sender: "neznamy", Message: "", UserID: "", Date: ""},
+			defaultYear:    2026,
+			wantMembers:    []Match{},
+			wantMonths:     []string{},
+			wantSearchText: "neznamy  ",
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := InferTransactionDetails(tc.tx, inferMembers, tc.defaultYear)
+
+			if !reflect.DeepEqual(got.Members, tc.wantMembers) {
+				t.Errorf("Members\n got  %v\n want %v", got.Members, tc.wantMembers)
+			}
+			if !reflect.DeepEqual(got.Months, tc.wantMonths) {
+				t.Errorf("Months\n got  %v\n want %v", got.Months, tc.wantMonths)
+			}
+			if got.SearchText != tc.wantSearchText {
+				t.Errorf("SearchText\n got  %q\n want %q", got.SearchText, tc.wantSearchText)
+			}
+		})
+	}
+}

go/internal/domain/matching/match_members.go

@@ -0,0 +1,131 @@
+package matching
+
+import (
+	"fuj-management/go/internal/domain/czech"
+	"strings"
+)
+
+// Confidence indicates how certain a member match is.
+type Confidence string
+
+const (
+	ConfidenceAuto   Confidence = "auto"
+	ConfidenceReview Confidence = "review"
+)
+
+// Match pairs a canonical member name with the confidence of the match.
+type Match struct {
+	Name       string
+	Confidence Confidence
+}
+
+var commonSurnames = map[string]bool{
+	"novak":    true,
+	"novakova": true,
+	"prach":    true,
+}
+
+// MatchMembers finds members mentioned in text and returns them with a
+// confidence level of "auto" (reliable) or "review" (needs human verification).
+//
+// Algorithm (ported verbatim from scripts/match_payments.py match_members):
+//  1. Exact short-circuit: if any member's full normalized name appears as whole
+//     words in normalize(text), return ONLY those matches as auto. This prevents
+//     nickname "tov" from matching inside surname "ottova".
+//  2. Per-member first-match-wins: full-name substring → first+last both present
+//     (any order) → nickname whole-word. Each yields auto.
+//  3. Review tier: last name (len≥4, not a common surname) → first name (len≥3)
+//     → single-part name (len≥4). Each yields review.
+//  4. Final filter: if any auto exists, drop all review.
+func MatchMembers(text string, memberNames []string) []Match {
+	normalizedText := czech.Normalize(text)
+
+	// Pass 1: exact short-circuit
+	var exactMatches []Match
+	for _, name := range memberNames {
+		variants := BuildNameVariants(name)
+		if len(variants) == 0 {
+			continue
+		}
+		fullName := variants[0]
+		if fullName != "" && wordIn(fullName, normalizedText) {
+			exactMatches = append(exactMatches, Match{Name: name, Confidence: ConfidenceAuto})
+		}
+	}
+	if len(exactMatches) > 0 {
+		return exactMatches
+	}
+
+	// Pass 2 + 3: fuzzy matching
+	var matches []Match
+	for _, name := range memberNames {
+		variants := BuildNameVariants(name)
+		fullName := ""
+		if len(variants) > 0 {
+			fullName = variants[0]
+		}
+		parts := strings.Fields(fullName)
+
+		// Auto tier
+		if fullName != "" && strings.Contains(normalizedText, fullName) {
+			matches = append(matches, Match{Name: name, Confidence: ConfidenceAuto})
+			continue
+		}
+		if len(parts) >= 2 {
+			if wordIn(parts[0], normalizedText) && wordIn(parts[len(parts)-1], normalizedText) {
+				matches = append(matches, Match{Name: name, Confidence: ConfidenceAuto})
+				continue
+			}
+		}
+		// Nickname check
+		if m := nicknameRe.FindStringSubmatch(name); m != nil {
+			nick := czech.Normalize(m[1])
+			if nick != "" && wordIn(nick, normalizedText) {
+				matches = append(matches, Match{Name: name, Confidence: ConfidenceAuto})
+				continue
+			}
+		}
+
+		// Review tier
+		if len(parts) >= 2 {
+			lastName := parts[len(parts)-1]
+			firstName := parts[0]
+			if len(lastName) >= 4 && !commonSurnames[lastName] && wordIn(lastName, normalizedText) {
+				matches = append(matches, Match{Name: name, Confidence: ConfidenceReview})
+				continue
+			}
+			if len(firstName) >= 3 && wordIn(firstName, normalizedText) {
+				matches = append(matches, Match{Name: name, Confidence: ConfidenceReview})
+				continue
+			}
+		} else if len(parts) == 1 {
+			if len(parts[0]) >= 4 && wordIn(parts[0], normalizedText) {
+				matches = append(matches, Match{Name: name, Confidence: ConfidenceReview})
+				continue
+			}
+		}
+	}
+
+	// Final filter: drop review if any auto exists
+	hasAuto := false
+	for _, m := range matches {
+		if m.Confidence == ConfidenceAuto {
+			hasAuto = true
+			break
+		}
+	}
+	if hasAuto {
+		filtered := matches[:0]
+		for _, m := range matches {
+			if m.Confidence == ConfidenceAuto {
+				filtered = append(filtered, m)
+			}
+		}
+		return filtered
+	}
+
+	if matches == nil {
+		return []Match{}
+	}
+	return matches
+}

go/internal/domain/matching/match_members_test.go

@@ -0,0 +1,156 @@
+package matching
+
+// Expected values verified against scripts/match_payments.py and
+// tests/test_match_members.py on 2026-05-06:
+//
+//	PYTHONPATH=scripts:. python3 -c '
+//	from match_payments import match_members
+//	MEMBERS = ["Henrietta Ottová", "Tomáš Němeček (Tov)", "František Vrbík (Štrúdl)", "Jana Nováková"]
+//	cases = [
+//	    ("Henrietta Ottová (Heny): 04/2026", "full name guard"),
+//	    ("platba ottova 04/2026", "ottova surname"),
+//	    ("Henrietta Ottová a Tomáš Němeček 04/2026", "two full names"),
+//	    ("Tov platba 04/2026", "nickname alone"),
+//	    ("Henrietta Ottova 04/2026", "no diacritics"),
+//	    ("Platba od Nemeček Tomas 04/2026", "reversed first+last"),
+//	    ("vrbik clenske", "last name only review"),
+//	    ("jana platba", "first name review"),
+//	    ("neznamy platebce", "no match"),
+//	]
+//	for text, label in cases: print(label + ":", match_members(text, MEMBERS))
+//	'
+//
+// Output:
+//
+//	full name guard: [('Henrietta Ottová', 'auto')]
+//	ottova surname: [('Henrietta Ottová', 'review')]
+//	two full names: [('Henrietta Ottová', 'auto'), ('Tomáš Němeček (Tov)', 'auto')]
+//	nickname alone: [('Tomáš Němeček (Tov)', 'auto')]
+//	no diacritics: [('Henrietta Ottová', 'auto')]
+//	reversed first+last: [('Tomáš Němeček (Tov)', 'auto')]
+//	last name only review: [('František Vrbík (Štrúdl)', 'review')]
+//	first name review: [('Jana Nováková', 'review')]
+//	no match: []
+
+import (
+	"testing"
+)
+
+var testMembers = []string{
+	"Henrietta Ottová",
+	"Tomáš Němeček (Tov)",
+	"František Vrbík (Štrúdl)",
+	"Jana Nováková",
+}
+
+func TestMatchMembers(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name         string
+		text         string
+		wantContains []string
+		wantExcludes []string
+		wantAllAuto  bool
+	}{
+		{
+			// Short-circuit: full name matches → "tov" inside "ottova" must NOT fire
+			name:         "full name in message returns only that member",
+			text:         "Henrietta Ottová (Heny): 04/2026",
+			wantContains: []string{"Henrietta Ottová"},
+			wantExcludes: []string{"Tomáš Němeček (Tov)"},
+			wantAllAuto:  true,
+		},
+		{
+			// "tov" is a substring of "ottova" — nickname must not match inside a surname
+			name:         "nickname tov not matched inside ottova",
+			text:         "platba ottova 04/2026",
+			wantExcludes: []string{"Tomáš Němeček (Tov)"},
+			wantAllAuto:  false,
+		},
+		{
+			name:         "two full names both auto",
+			text:         "Henrietta Ottová a Tomáš Němeček 04/2026",
+			wantContains: []string{"Henrietta Ottová", "Tomáš Němeček (Tov)"},
+			wantAllAuto:  true,
+		},
+		{
+			name:         "nickname alone matches correctly",
+			text:         "Tov platba 04/2026",
+			wantContains: []string{"Tomáš Němeček (Tov)"},
+			wantAllAuto:  true,
+		},
+		{
+			name:         "full name without diacritics auto",
+			text:         "Henrietta Ottova 04/2026",
+			wantContains: []string{"Henrietta Ottová"},
+			wantExcludes: []string{"Tomáš Němeček (Tov)"},
+			wantAllAuto:  true,
+		},
+		{
+			name:         "first and last name reversed auto",
+			text:         "Platba od Nemeček Tomas 04/2026",
+			wantContains: []string{"Tomáš Němeček (Tov)"},
+			wantAllAuto:  true,
+		},
+		{
+			// Last name alone (len≥4, not a common surname) → review confidence
+			name:         "last name only yields review",
+			text:         "vrbik clenske",
+			wantContains: []string{"František Vrbík (Štrúdl)"},
+			wantAllAuto:  false,
+		},
+		{
+			// First name alone (len≥3) → review confidence
+			name:         "first name only yields review",
+			text:         "jana platba",
+			wantContains: []string{"Jana Nováková"},
+			wantAllAuto:  false,
+		},
+		{
+			name:         "no match returns empty slice",
+			text:         "neznamy platebce",
+			wantContains: nil,
+			wantAllAuto:  false,
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := MatchMembers(tc.text, testMembers)
+
+			// Check required members are present
+			for _, want := range tc.wantContains {
+				found := false
+				for _, m := range got {
+					if m.Name == want {
+						found = true
+						break
+					}
+				}
+				if !found {
+					t.Errorf("MatchMembers(%q): want %q in result, got %v", tc.text, want, got)
+				}
+			}
+
+			// Check excluded members are absent
+			for _, exclude := range tc.wantExcludes {
+				for _, m := range got {
+					if m.Name == exclude {
+						t.Errorf("MatchMembers(%q): %q should not be in result, got %v", tc.text, exclude, got)
+					}
+				}
+			}
+
+			// Check all-auto constraint
+			if tc.wantAllAuto {
+				for _, m := range got {
+					if m.Confidence != ConfidenceAuto {
+						t.Errorf("MatchMembers(%q): expected all auto, got %v", tc.text, got)
+					}
+				}
+			}
+		})
+	}
+}

go/internal/domain/matching/name_variants.go

@@ -0,0 +1,59 @@
+package matching
+
+import (
+	"fuj-management/go/internal/domain/czech"
+	"regexp"
+	"strings"
+)
+
+var (
+	nicknameRe      = regexp.MustCompile(`\(([^)]+)\)`)
+	nicknameStripRe = regexp.MustCompile(`\s*\([^)]*\)\s*`)
+)
+
+// BuildNameVariants returns searchable lowercase ASCII variants of a member name.
+//
+// Example: "František Vrbík (Štrúdl)" → ["frantisek vrbik", "strudl", "vrbik", "frantisek"]
+//
+// variants[0] is always the full normalized base name (no nickname). MatchMembers relies on
+// this invariant for the exact short-circuit pass. Variants shorter than 3 characters are
+// dropped.
+//
+// Ports scripts/match_payments.py _build_name_variants.
+func BuildNameVariants(name string) []string {
+	var nickname string
+	if m := nicknameRe.FindStringSubmatch(name); m != nil {
+		nickname = m[1]
+	}
+
+	base := strings.TrimSpace(nicknameStripRe.ReplaceAllString(name, " "))
+	normalizedBase := czech.Normalize(base)
+	normalizedNick := czech.Normalize(nickname)
+
+	variants := []string{normalizedBase}
+	if normalizedNick != "" {
+		variants = append(variants, normalizedNick)
+	}
+
+	parts := strings.Fields(normalizedBase)
+	if len(parts) >= 2 {
+		variants = append(variants, parts[len(parts)-1]) // last name
+		variants = append(variants, parts[0])            // first name
+	}
+
+	filtered := variants[:0]
+	for _, v := range variants {
+		if len(v) >= 3 {
+			filtered = append(filtered, v)
+		}
+	}
+	return filtered
+}
+
+// wordIn returns true if needle appears as a whole word in haystack.
+// Both needle and haystack must already be ASCII-folded (via czech.Normalize).
+func wordIn(needle, haystack string) bool {
+	pattern := `\b` + regexp.QuoteMeta(needle) + `\b`
+	matched, _ := regexp.MatchString(pattern, haystack)
+	return matched
+}

go/internal/domain/matching/name_variants_test.go

@@ -0,0 +1,62 @@
+package matching
+
+// Expected values verified against scripts/match_payments.py on 2026-05-06:
+//
+//	PYTHONPATH=scripts:. python3 -c '
+//	from match_payments import _build_name_variants
+//	for n in ["František Vrbík (Štrúdl)", "Tov (St)", "Jana", "  Petr  Novák  ( Jenda ) "]:
+//	    print(repr(n), "->", _build_name_variants(n))
+//	'
+//
+// Output:
+//
+//	'František Vrbík (Štrúdl)' -> ['frantisek vrbik', 'strudl', 'vrbik', 'frantisek']
+//	'Tov (St)' -> ['tov']
+//	'Jana' -> ['jana']
+//	'  Petr  Novák  ( Jenda ) ' -> ['petr  novak', ' jenda ', 'novak', 'petr']
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestBuildNameVariants(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name  string
+		input string
+		want  []string
+	}{
+		{
+			name:  "full name with nickname",
+			input: "František Vrbík (Štrúdl)",
+			want:  []string{"frantisek vrbik", "strudl", "vrbik", "frantisek"},
+		},
+		{
+			name:  "nickname too short filtered out",
+			input: "Tov (St)",
+			want:  []string{"tov"},
+		},
+		{
+			name:  "single-part name no nickname",
+			input: "Jana",
+			want:  []string{"jana"},
+		},
+		{
+			name:  "extra whitespace inside parens preserved by normalize",
+			input: "  Petr  Novák  ( Jenda ) ",
+			want:  []string{"petr  novak", " jenda ", "novak", "petr"},
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := BuildNameVariants(tc.input)
+			if !reflect.DeepEqual(got, tc.want) {
+				t.Errorf("BuildNameVariants(%q)\n got  %q\n want %q", tc.input, got, tc.want)
+			}
+		})
+	}
+}

go/internal/domain/reconcile/reconcile.go

@@ -0,0 +1,403 @@
+// Package reconcile ports the three-phase payment reconciliation from scripts/match_payments.py.
+package reconcile
+
+import (
+	"fuj-management/go/internal/domain/czech"
+	"fuj-management/go/internal/domain/matching"
+	"regexp"
+	"strings"
+)
+
+// ExceptionKey identifies a fee override by normalized member name and period.
+type ExceptionKey struct {
+	Name   string // czech.Normalize(memberName)
+	Period string // czech.Normalize("YYYY-MM")
+}
+
+// Exception is a manual fee override for one member in one period.
+type Exception struct {
+	Amount int
+	Note   string
+}
+
+// FeeData holds the expected fee and attendance data for one member in one month.
+type FeeData struct {
+	Expected         int
+	IsUnknown        bool // true when junior has exactly 1 session (manual review; Python sentinel "?")
+	Attendance       int
+	JuniorAttendance int // junior-tab sessions; used for the :NJ,MA breakdown in the juniors view
+	AdultAttendance  int // adult-tab sessions for J-tier members; used for the :NJ,MA breakdown
+}
+
+// Member is one row from the attendance sheet.
+type Member struct {
+	Name string
+	Tier string
+	Fees map[string]FeeData // month ("YYYY-MM") → fee data
+}
+
+// Transaction is one payment row from the payments sheet.
+// Date must already be a "YYYY-MM-DD" string (convert with matching.FormatDate before calling).
+// InferredAmount, when non-nil, replaces Amount when person and purpose are pre-matched.
+type Transaction struct {
+	Date           string
+	Amount         float64
+	ManualFix      string   // "manual fix" column; non-empty disables re-inference
+	Person         string   // comma-separated canonical names (empty → use inference)
+	Purpose        string   // comma-separated "YYYY-MM" or "other:…" (empty → use inference)
+	InferredAmount *float64 // nil → fall back to Amount
+	Sender         string
+	VS             string // Variabilní symbol (Czech variable payment symbol)
+	Message        string
+	BankID         string
+	SyncID         string
+	UserID         string
+}
+
+// TxEntry is the portion of a payment allocated to a single member+month.
+type TxEntry struct {
+	Amount     float64
+	Date       string
+	Sender     string
+	Message    string
+	Confidence string
+}
+
+// OtherEntry is a payment with purpose "other:…" allocated to a member.
+type OtherEntry struct {
+	Amount     float64
+	Date       string
+	Sender     string
+	Message    string
+	Purpose    string
+	Confidence string
+}
+
+// MonthData is the ledger state for one member in one month.
+type MonthData struct {
+	Expected         int
+	IsUnknown        bool // mirrors FeeData.IsUnknown; not overridden by exceptions
+	OriginalExpected int
+	AttendanceCount  int
+	JuniorAttendance int // junior-tab sessions; for :NJ,MA breakdown in juniors view
+	AdultAttendance  int // adult-tab sessions; for :NJ,MA breakdown
+	Exception        *Exception
+	Paid             float64
+	Transactions     []TxEntry
+}
+
+// MemberResult is the reconciled ledger for one member.
+type MemberResult struct {
+	Tier              string
+	Months            map[string]MonthData
+	OtherTransactions []OtherEntry
+	TotalBalance      int
+}
+
+// Result is the top-level output of Reconcile.
+type Result struct {
+	Members   map[string]MemberResult
+	Unmatched []Transaction
+	Credits   map[string]int // final balance for every member (may be negative)
+}
+
+var questionMarkRe = regexp.MustCompile(`\[\?\]\s*`)
+
+// canonicalMemberKey returns a diacritic-, case-, and whitespace-insensitive key
+// used to resolve Person-column values that drift from canonical attendance-sheet names.
+// Ports scripts/match_payments.py canonical_member_key.
+func canonicalMemberKey(name string) string {
+	return strings.Join(strings.Fields(czech.Normalize(name)), " ")
+}
+
+type monthExpected struct {
+	month    string
+	expected int
+}
+
+// Reconcile matches transactions to members and months using two allocation phases:
+//  1. Fill-first: iterate matched months in user-supplied order, allocating min(remaining,
+//     deficit) to each month where deficit = expected − already-paid. Surplus → credit.
+//     Handles both the "greedy" (payment covers all) and "partial" cases in one pass.
+//  2. Even-split fallback: all expected fees are 0 (prepayment) → divide equally.
+//
+// defaultYear seeds czech.ParseMonthReferences in the inference fallback.
+// Pass time.Now().Year() in production; pass a fixed year in tests.
+//
+// Ports scripts/match_payments.py reconcile.
+func Reconcile(
+	members []Member,
+	sortedMonths []string,
+	transactions []Transaction,
+	exceptions map[ExceptionKey]Exception,
+	defaultYear int,
+) Result {
+	memberNames := make([]string, len(members))
+	memberTiers := make(map[string]string, len(members))
+	memberFees := make(map[string]map[string]FeeData, len(members))
+
+	for i, m := range members {
+		memberNames[i] = m.Name
+		memberTiers[m.Name] = m.Tier
+		memberFees[m.Name] = m.Fees
+	}
+
+	// Map canonical key → first attendance-sheet name with that key, so Person cells
+	// that drift in diacritics/case/whitespace still resolve to the canonical name.
+	canonicalByKey := make(map[string]string, len(memberNames))
+	for _, name := range memberNames {
+		key := canonicalMemberKey(name)
+		if _, exists := canonicalByKey[key]; !exists {
+			canonicalByKey[key] = name
+		}
+	}
+
+	if exceptions == nil {
+		exceptions = map[ExceptionKey]Exception{}
+	}
+
+	// Initialise ledger
+	ledger := make(map[string]map[string]MonthData, len(memberNames))
+	otherLedger := make(map[string][]OtherEntry, len(memberNames))
+
+	for _, name := range memberNames {
+		ledger[name] = make(map[string]MonthData, len(sortedMonths))
+		otherLedger[name] = []OtherEntry{}
+		for _, m := range sortedMonths {
+			fd := memberFees[name][m]
+			originalExpected := fd.Expected
+			attendanceCount := fd.Attendance
+
+			var expected int
+			var exInfo *Exception
+			exKey := ExceptionKey{
+				Name:   czech.Normalize(name),
+				Period: czech.Normalize(m),
+			}
+			if ex, ok := exceptions[exKey]; ok {
+				expected = ex.Amount
+				exCopy := ex
+				exInfo = &exCopy
+			} else {
+				expected = originalExpected
+			}
+
+			ledger[name][m] = MonthData{
+				Expected:         expected,
+				IsUnknown:        fd.IsUnknown,
+				OriginalExpected: originalExpected,
+				AttendanceCount:  attendanceCount,
+				JuniorAttendance: fd.JuniorAttendance,
+				AdultAttendance:  fd.AdultAttendance,
+				Exception:        exInfo,
+				Paid:             0,
+				Transactions:     []TxEntry{},
+			}
+		}
+	}
+
+	var unmatched []Transaction
+	credits := make(map[string]int, len(memberNames))
+
+	for _, tx := range transactions {
+		personStr := strings.TrimSpace(tx.Person)
+		purposeStr := strings.TrimSpace(tx.Purpose)
+		personStr = questionMarkRe.ReplaceAllString(personStr, "")
+		isOther := strings.HasPrefix(strings.ToLower(purposeStr), "other:")
+
+		var matchedMembers []matching.Match
+		var matchedMonths []string
+		var amount float64
+
+		if personStr != "" && purposeStr != "" {
+			for p := range strings.SplitSeq(personStr, ",") {
+				p = strings.TrimSpace(p)
+				if p != "" {
+					matchedMembers = append(matchedMembers, matching.Match{
+						Name:       p,
+						Confidence: matching.ConfidenceAuto,
+					})
+				}
+			}
+			if isOther {
+				matchedMonths = []string{purposeStr}
+			} else {
+				for m := range strings.SplitSeq(purposeStr, ",") {
+					m = strings.TrimSpace(m)
+					if m != "" {
+						matchedMonths = append(matchedMonths, m)
+					}
+				}
+			}
+			if tx.InferredAmount != nil {
+				amount = *tx.InferredAmount
+			} else {
+				amount = tx.Amount
+			}
+		} else {
+			// Inference fallback for rows not yet processed by infer_payments.py
+			inferred := matching.InferTransactionDetails(
+				matching.Transaction{
+					Sender:  tx.Sender,
+					Message: tx.Message,
+					UserID:  tx.UserID,
+					Date:    tx.Date,
+				},
+				memberNames,
+				defaultYear,
+			)
+			matchedMembers = inferred.Members
+			matchedMonths = inferred.Months
+			amount = tx.Amount
+		}
+
+		if len(matchedMembers) == 0 || len(matchedMonths) == 0 {
+			unmatched = append(unmatched, tx)
+			continue
+		}
+
+		if isOther {
+			nAlloc := len(matchedMembers)
+			perAlloc := 0.0
+			if nAlloc > 0 {
+				perAlloc = amount / float64(nAlloc)
+			}
+			for _, m := range matchedMembers {
+				memberName := canonicalByKey[canonicalMemberKey(m.Name)]
+				if memberName != "" {
+					otherLedger[memberName] = append(otherLedger[memberName], OtherEntry{
+						Amount:     perAlloc,
+						Date:       tx.Date,
+						Sender:     tx.Sender,
+						Message:    tx.Message,
+						Purpose:    purposeStr,
+						Confidence: string(m.Confidence),
+					})
+				}
+			}
+			continue
+		}
+
+		memberShare := 0.0
+		if len(matchedMembers) > 0 {
+			memberShare = amount / float64(len(matchedMembers))
+		}
+
+		for _, m := range matchedMembers {
+			memberName := canonicalByKey[canonicalMemberKey(m.Name)]
+			if memberName == "" {
+				unmatched = append(unmatched, tx)
+				continue
+			}
+
+			var inWindow []monthExpected
+			outCount := 0
+			for _, month := range matchedMonths {
+				if md, ok := ledger[memberName][month]; ok {
+					inWindow = append(inWindow, monthExpected{month: month, expected: md.Expected})
+				} else {
+					outCount++
+				}
+			}
+
+			nTotal := len(matchedMonths)
+			outCredit := 0.0
+			if outCount > 0 && nTotal > 0 {
+				outCredit = memberShare / float64(nTotal) * float64(outCount)
+				credits[memberName] += int(outCredit)
+			}
+
+			inWindowShare := memberShare - outCredit
+
+			if len(inWindow) == 0 {
+				continue
+			}
+
+			totalExpected := 0
+			for _, mw := range inWindow {
+				totalExpected += mw.expected
+			}
+
+			if totalExpected > 0 {
+				// Fill-first: iterate inWindow in matched-months order (chronological by
+				// convention), allocating min(remaining, deficit) to each month. Deficit
+				// is net of what prior transactions already paid, so a second payment on
+				// the same months correctly fills only what remains due. Any surplus after
+				// all deficits are covered goes to the credit bucket.
+				remaining := inWindowShare
+				for _, mw := range inWindow {
+					md := ledger[memberName][mw.month]
+					deficit := float64(mw.expected) - md.Paid
+					if deficit < 0 {
+						deficit = 0
+					}
+					alloc := remaining
+					if deficit < alloc {
+						alloc = deficit
+					}
+					if alloc <= 0 {
+						continue
+					}
+					md.Paid += alloc
+					md.Transactions = append(md.Transactions, TxEntry{
+						Amount:     alloc,
+						Date:       tx.Date,
+						Sender:     tx.Sender,
+						Message:    tx.Message,
+						Confidence: string(m.Confidence),
+					})
+					ledger[memberName][mw.month] = md
+					remaining -= alloc
+				}
+				if remaining > 0 {
+					credits[memberName] += int(remaining)
+				}
+			} else {
+				// Even-split fallback: prepayment before attendance recorded
+				perMonth := inWindowShare / float64(len(inWindow))
+				for _, mw := range inWindow {
+					md := ledger[memberName][mw.month]
+					md.Paid += perMonth
+					md.Transactions = append(md.Transactions, TxEntry{
+						Amount:     perMonth,
+						Date:       tx.Date,
+						Sender:     tx.Sender,
+						Message:    tx.Message,
+						Confidence: string(m.Confidence),
+					})
+					ledger[memberName][mw.month] = md
+				}
+			}
+		}
+	}
+
+	// Final total balances: window balance + out-of-window credits accumulated above
+	finalBalances := make(map[string]int, len(memberNames))
+	for _, name := range memberNames {
+		windowBalance := 0
+		for _, mdata := range ledger[name] {
+			windowBalance += int(mdata.Paid) - mdata.Expected
+		}
+		finalBalances[name] = windowBalance + credits[name]
+	}
+
+	membersResult := make(map[string]MemberResult, len(memberNames))
+	for _, name := range memberNames {
+		membersResult[name] = MemberResult{
+			Tier:              memberTiers[name],
+			Months:            ledger[name],
+			OtherTransactions: otherLedger[name],
+			TotalBalance:      finalBalances[name],
+		}
+	}
+
+	if unmatched == nil {
+		unmatched = []Transaction{}
+	}
+
+	return Result{
+		Members:   membersResult,
+		Unmatched: unmatched,
+		Credits:   finalBalances,
+	}
+}

go/internal/domain/reconcile/reconcile_test.go

@@ -0,0 +1,415 @@
+package reconcile
+
+// Expected values verified against scripts/match_payments.py on 2026-05-06:
+//
+//	PYTHONPATH=scripts:. python3 -m unittest tests.test_reconcile_exceptions tests.test_match_payments -v
+//
+// All Python test cases are ported below. Additional Go-only cases are marked with [Go].
+
+import (
+	"math"
+	"testing"
+)
+
+const defaultYear = 2026
+
+// tx builds a pre-matched Transaction (person+purpose already filled in).
+// InferredAmount is left nil so Amount is used directly, matching the Python
+// _tx helper where inferred_amount == amount.
+func tx(person, purpose string, amount float64) Transaction {
+	return Transaction{
+		Date:    "2026-01-01",
+		Amount:  amount,
+		Person:  person,
+		Purpose: purpose,
+		Sender:  "Sender",
+		Message: "fee",
+	}
+}
+
+func TestReconcileExceptionOverride(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Alice", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 4}}}}
+	exceptions := map[ExceptionKey]Exception{
+		{Name: "alice", Period: "2026-01"}: {Amount: 400, Note: "Test exception"},
+	}
+	txs := []Transaction{{
+		Date: "2026-01-05", Amount: 400,
+		Person: "Alice", Purpose: "2026-01", Sender: "Alice Sender", Message: "fee",
+	}}
+
+	result := Reconcile(members, []string{"2026-01"}, txs, exceptions, defaultYear)
+
+	jan := result.Members["Alice"].Months["2026-01"]
+	if jan.Expected != 400 {
+		t.Errorf("Expected override to 400, got %d", jan.Expected)
+	}
+	if jan.Paid != 400 {
+		t.Errorf("Paid want 400, got %f", jan.Paid)
+	}
+	if result.Members["Alice"].TotalBalance != 0 {
+		t.Errorf("TotalBalance want 0, got %d", result.Members["Alice"].TotalBalance)
+	}
+}
+
+func TestReconcileFallbackToAttendance(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Alice", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 4}}}}
+
+	result := Reconcile(members, []string{"2026-01"}, nil, nil, defaultYear)
+
+	if result.Members["Alice"].Months["2026-01"].Expected != 750 {
+		t.Errorf("Expected 750 when no exception, got %d", result.Members["Alice"].Months["2026-01"].Expected)
+	}
+}
+
+func TestReconcileGreedyExactMatch(t *testing.T) {
+	t.Parallel()
+	members := []Member{{
+		Name: "Alice", Tier: "A",
+		Fees: map[string]FeeData{
+			"2026-02": {Expected: 750, Attendance: 3},
+			"2026-03": {Expected: 350, Attendance: 3},
+			"2026-04": {Expected: 150, Attendance: 2},
+		},
+	}}
+	sortedMonths := []string{"2026-02", "2026-03", "2026-04"}
+
+	result := Reconcile(members, sortedMonths, []Transaction{tx("Alice", "2026-02, 2026-03, 2026-04", 1250)}, nil, defaultYear)
+
+	months := result.Members["Alice"].Months
+	if int(months["2026-02"].Paid) != 750 {
+		t.Errorf("2026-02 paid want 750, got %f", months["2026-02"].Paid)
+	}
+	if int(months["2026-03"].Paid) != 350 {
+		t.Errorf("2026-03 paid want 350, got %f", months["2026-03"].Paid)
+	}
+	if int(months["2026-04"].Paid) != 150 {
+		t.Errorf("2026-04 paid want 150, got %f", months["2026-04"].Paid)
+	}
+}
+
+func TestReconcileGreedyOverpaymentGoesToCredit(t *testing.T) {
+	t.Parallel()
+	members := []Member{{
+		Name: "Alice", Tier: "A",
+		Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 3}, "2026-02": {Expected: 750, Attendance: 3}},
+	}}
+	sortedMonths := []string{"2026-01", "2026-02"}
+
+	result := Reconcile(members, sortedMonths, []Transaction{tx("Alice", "2026-01, 2026-02", 2000)}, nil, defaultYear)
+
+	months := result.Members["Alice"].Months
+	if int(months["2026-01"].Paid) != 750 {
+		t.Errorf("2026-01 paid want 750, got %f", months["2026-01"].Paid)
+	}
+	if int(months["2026-02"].Paid) != 750 {
+		t.Errorf("2026-02 paid want 750, got %f", months["2026-02"].Paid)
+	}
+	if result.Credits["Alice"] != 500 {
+		t.Errorf("credits want 500, got %d", result.Credits["Alice"])
+	}
+}
+
+func TestReconcileUnderpaymentFillsEarliestFirst(t *testing.T) {
+	t.Parallel()
+	members := []Member{{
+		Name: "Alice", Tier: "A",
+		Fees: map[string]FeeData{"2026-02": {Expected: 750, Attendance: 3}, "2026-03": {Expected: 350, Attendance: 3}, "2026-04": {Expected: 750, Attendance: 3}},
+	}}
+	sortedMonths := []string{"2026-02", "2026-03", "2026-04"}
+
+	result := Reconcile(members, sortedMonths, []Transaction{tx("Alice", "2026-02, 2026-03, 2026-04", 1250)}, nil, defaultYear)
+
+	months := result.Members["Alice"].Months
+	// 02 filled first (750), then 03 (350), then remainder 150 to 04
+	if math.Abs(months["2026-02"].Paid-750) > 0.01 {
+		t.Errorf("02: want 750, got %f", months["2026-02"].Paid)
+	}
+	if math.Abs(months["2026-03"].Paid-350) > 0.01 {
+		t.Errorf("03: want 350, got %f", months["2026-03"].Paid)
+	}
+	if math.Abs(months["2026-04"].Paid-150) > 0.01 {
+		t.Errorf("04: want 150, got %f", months["2026-04"].Paid)
+	}
+}
+
+func TestReconcileSingleMonthUnchanged(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Alice", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 3}}}}
+
+	result := Reconcile(members, []string{"2026-01"}, []Transaction{tx("Alice", "2026-01", 750)}, nil, defaultYear)
+
+	if math.Abs(result.Members["Alice"].Months["2026-01"].Paid-750) > 0.01 {
+		t.Errorf("single month want 750, got %f", result.Members["Alice"].Months["2026-01"].Paid)
+	}
+}
+
+func TestReconcileTwoMembersMultiMonth(t *testing.T) {
+	t.Parallel()
+	members := []Member{
+		{Name: "Alice", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 3}, "2026-02": {Expected: 350, Attendance: 3}}},
+		{Name: "Bob", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 3}, "2026-02": {Expected: 350, Attendance: 3}}},
+	}
+	sortedMonths := []string{"2026-01", "2026-02"}
+
+	result := Reconcile(members, sortedMonths, []Transaction{tx("Alice, Bob", "2026-01, 2026-02", 2200)}, nil, defaultYear)
+
+	for _, name := range []string{"Alice", "Bob"} {
+		months := result.Members[name].Months
+		if math.Abs(months["2026-01"].Paid-750) > 0.01 {
+			t.Errorf("%s 2026-01 paid want 750, got %f", name, months["2026-01"].Paid)
+		}
+		if math.Abs(months["2026-02"].Paid-350) > 0.01 {
+			t.Errorf("%s 2026-02 paid want 350, got %f", name, months["2026-02"].Paid)
+		}
+	}
+}
+
+func TestReconcileEvenSplitFallbackWhenNoExpected(t *testing.T) {
+	t.Parallel()
+	members := []Member{{
+		Name: "Alice", Tier: "A",
+		Fees: map[string]FeeData{"2026-01": {Expected: 0, Attendance: 0}, "2026-02": {Expected: 0, Attendance: 0}},
+	}}
+	sortedMonths := []string{"2026-01", "2026-02"}
+
+	result := Reconcile(members, sortedMonths, []Transaction{tx("Alice", "2026-01, 2026-02", 300)}, nil, defaultYear)
+
+	months := result.Members["Alice"].Months
+	if math.Abs(months["2026-01"].Paid-150) > 0.01 {
+		t.Errorf("2026-01 paid want 150, got %f", months["2026-01"].Paid)
+	}
+	if math.Abs(months["2026-02"].Paid-150) > 0.01 {
+		t.Errorf("2026-02 paid want 150, got %f", months["2026-02"].Paid)
+	}
+}
+
+func TestReconcileDiacriticsTolerantPersonMatching(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Mária Maco", Tier: "A", Fees: map[string]FeeData{"2026-04": {Expected: 750, Attendance: 4}}}}
+	txFn := func(person string) Transaction {
+		return Transaction{
+			Date: "2026-04-15", Amount: 750, Person: person, Purpose: "2026-04",
+			Sender: "Maco Family", Message: "fee",
+		}
+	}
+
+	cases := []struct {
+		name   string
+		person string
+	}{
+		{"without diacritics", "Maria Maco"},
+		{"extra whitespace", "Mária  Maco"},
+		{"lowercase", "mária maco"},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			result := Reconcile(members, []string{"2026-04"}, []Transaction{txFn(tc.person)}, nil, defaultYear)
+
+			paid := result.Members["Mária Maco"].Months["2026-04"].Paid
+			if paid != 750 {
+				t.Errorf("%s: paid want 750, got %f", tc.name, paid)
+			}
+			if len(result.Unmatched) != 0 {
+				t.Errorf("%s: want no unmatched, got %v", tc.name, result.Unmatched)
+			}
+		})
+	}
+}
+
+func TestReconcileTrulyUnknownPersonIsUnmatched(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Mária Maco", Tier: "A", Fees: map[string]FeeData{"2026-04": {Expected: 750, Attendance: 4}}}}
+	txs := []Transaction{{
+		Date: "2026-04-15", Amount: 750,
+		Person: "Někdo Neznámý", Purpose: "2026-04",
+		Sender: "Neznámý", Message: "fee",
+	}}
+
+	result := Reconcile(members, []string{"2026-04"}, txs, nil, defaultYear)
+
+	if result.Members["Mária Maco"].Months["2026-04"].Paid != 0 {
+		t.Errorf("unknown person must not credit the member")
+	}
+	if len(result.Unmatched) != 1 {
+		t.Errorf("want 1 unmatched, got %d", len(result.Unmatched))
+	}
+}
+
+// [Go] Test that [?] markers are stripped from the Person field before lookup.
+func TestReconcileQuestionMarkMarkerStripped(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Alice", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 3}}}}
+	txs := []Transaction{{
+		Date: "2026-01-01", Amount: 750,
+		Person: "[?] Alice", Purpose: "2026-01",
+		Sender: "Bank", Message: "fee",
+	}}
+
+	result := Reconcile(members, []string{"2026-01"}, txs, nil, defaultYear)
+
+	if result.Members["Alice"].Months["2026-01"].Paid != 750 {
+		t.Errorf("[?] stripping: want 750 paid, got %f", result.Members["Alice"].Months["2026-01"].Paid)
+	}
+}
+
+// [Go] Purpose "other:shirt" puts payment in OtherTransactions, not in month ledger.
+func TestReconcileOtherPurpose(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Alice", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 3}}}}
+	txs := []Transaction{{
+		Date: "2026-01-01", Amount: 300,
+		Person: "Alice", Purpose: "other:shirt",
+		Sender: "Bank", Message: "shirt order",
+	}}
+
+	result := Reconcile(members, []string{"2026-01"}, txs, nil, defaultYear)
+
+	if result.Members["Alice"].Months["2026-01"].Paid != 0 {
+		t.Errorf("other: purpose must not touch month ledger")
+	}
+	others := result.Members["Alice"].OtherTransactions
+	if len(others) != 1 {
+		t.Fatalf("want 1 OtherTransaction, got %d", len(others))
+	}
+	if math.Abs(others[0].Amount-300) > 0.01 {
+		t.Errorf("OtherEntry.Amount want 300, got %f", others[0].Amount)
+	}
+	if others[0].Purpose != "other:shirt" {
+		t.Errorf("OtherEntry.Purpose want %q, got %q", "other:shirt", others[0].Purpose)
+	}
+}
+
+// [Go] Months outside sortedMonths go to credit, not to the window ledger.
+func TestReconcileOutOfWindowGoesToCredit(t *testing.T) {
+	t.Parallel()
+	// Window shows only 2026-01. Transaction references 2026-01 (in) and 2026-02 (out).
+	members := []Member{{Name: "Alice", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 600, Attendance: 3}}}}
+	txs := []Transaction{{
+		Date: "2026-01-01", Amount: 1200,
+		Person: "Alice", Purpose: "2026-01, 2026-02",
+		Sender: "Bank", Message: "Q1",
+	}}
+
+	result := Reconcile(members, []string{"2026-01"}, txs, nil, defaultYear)
+
+	// member_share = 1200 (one member)
+	// out_credit = 1200 / 2 * 1 = 600
+	// in_window_share = 600
+	// in_window = [(2026-01, 600)], total_expected = 600 → greedy: paid = 600, no overflow
+	if math.Abs(result.Members["Alice"].Months["2026-01"].Paid-600) > 0.01 {
+		t.Errorf("in-window paid want 600, got %f", result.Members["Alice"].Months["2026-01"].Paid)
+	}
+	// total_balance = int(600) - 600 (window) + 600 (out credit) = 600
+	if result.Members["Alice"].TotalBalance != 600 {
+		t.Errorf("TotalBalance want 600, got %d", result.Members["Alice"].TotalBalance)
+	}
+}
+
+// [Go] No person/purpose → inference fallback resolves sender name and date month.
+func TestReconcileInferenceFallback(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Tomáš Němeček", Tier: "A", Fees: map[string]FeeData{"2026-04": {Expected: 750, Attendance: 3}}}}
+	txs := []Transaction{{
+		Date: "2026-04-15", Amount: 750,
+		// Person and Purpose are empty → inference path
+		Sender:  "Tomas Nemecek",
+		Message: "clenske 04/2026",
+	}}
+
+	result := Reconcile(members, []string{"2026-04"}, txs, nil, defaultYear)
+
+	if math.Abs(result.Members["Tomáš Němeček"].Months["2026-04"].Paid-750) > 0.01 {
+		t.Errorf("inference fallback: want 750 paid, got %f", result.Members["Tomáš Němeček"].Months["2026-04"].Paid)
+	}
+}
+
+// [Go] Transaction with no match at all ends up in Unmatched; ledger unchanged.
+func TestReconcileNoMatchGoesToUnmatched(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Alice", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 3}}}}
+	txs := []Transaction{{
+		Date: "2026-01-01", Amount: 500,
+		// empty person+purpose and sender name not matching any member
+		Sender: "Unknown Corp", Message: "invoice",
+	}}
+
+	result := Reconcile(members, []string{"2026-01"}, txs, nil, defaultYear)
+
+	if len(result.Unmatched) != 1 {
+		t.Errorf("want 1 unmatched, got %d", len(result.Unmatched))
+	}
+	if result.Members["Alice"].Months["2026-01"].Paid != 0 {
+		t.Errorf("unmatched tx must not touch ledger")
+	}
+}
+
+// [Go] Empty transaction list leaves every month at paid=0 and balance=–expected.
+func TestReconcileNoTransactionsAllUnpaid(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Alice", Tier: "A", Fees: map[string]FeeData{"2026-01": {Expected: 750, Attendance: 3}}}}
+
+	result := Reconcile(members, []string{"2026-01"}, nil, nil, defaultYear)
+
+	if result.Members["Alice"].Months["2026-01"].Paid != 0 {
+		t.Errorf("no txs: want paid=0, got %f", result.Members["Alice"].Months["2026-01"].Paid)
+	}
+	if result.Members["Alice"].TotalBalance != -750 {
+		t.Errorf("no txs: want balance -750, got %d", result.Members["Alice"].TotalBalance)
+	}
+	if len(result.Unmatched) != 0 {
+		t.Errorf("no txs: want empty unmatched, got %v", result.Unmatched)
+	}
+}
+
+// Payment < total expected → fill earliest months first, spill remainder to later.
+func TestUnderpaymentFillsEarliestFirst(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Alice", Tier: "A", Fees: map[string]FeeData{
+		"2026-02": {Expected: 750, Attendance: 3},
+		"2026-03": {Expected: 350, Attendance: 3},
+		"2026-04": {Expected: 750, Attendance: 3},
+	}}}
+	txs := []Transaction{tx("Alice", "2026-02, 2026-03, 2026-04", 1250)}
+
+	result := Reconcile(members, []string{"2026-02", "2026-03", "2026-04"}, txs, nil, defaultYear)
+	months := result.Members["Alice"].Months
+
+	// 02 filled first (750), then 03 (350), then remainder 150 to 04
+	if math.Abs(months["2026-02"].Paid-750) > 0.01 {
+		t.Errorf("02: want 750, got %f", months["2026-02"].Paid)
+	}
+	if math.Abs(months["2026-03"].Paid-350) > 0.01 {
+		t.Errorf("03: want 350, got %f", months["2026-03"].Paid)
+	}
+	if math.Abs(months["2026-04"].Paid-150) > 0.01 {
+		t.Errorf("04: want 150, got %f", months["2026-04"].Paid)
+	}
+}
+
+// Prior txn fills 02 partially; later txn finishes 02 then spills to 03.
+func TestFillFirstAcrossTwoTransactions(t *testing.T) {
+	t.Parallel()
+	members := []Member{{Name: "Matyáš", Tier: "A", Fees: map[string]FeeData{
+		"2026-02": {Expected: 500, Attendance: 2},
+		"2026-03": {Expected: 250, Attendance: 1},
+	}}}
+	sortedMonths := []string{"2026-02", "2026-03"}
+	txs := []Transaction{
+		tx("Matyáš", "2026-02", 200),
+		tx("Matyáš", "2026-02, 2026-03", 550),
+	}
+
+	result := Reconcile(members, sortedMonths, txs, nil, defaultYear)
+	months := result.Members["Matyáš"].Months
+
+	if math.Abs(months["2026-02"].Paid-500) > 0.01 {
+		t.Errorf("02: want 500, got %f", months["2026-02"].Paid)
+	}
+	if math.Abs(months["2026-03"].Paid-250) > 0.01 {
+		t.Errorf("03: want 250, got %f", months["2026-03"].Paid)
+	}
+}

go/internal/domain/synch/synch.go

@@ -0,0 +1,65 @@
+// Package synch ports the bank-sync deduplication helper from
+// scripts/sync_fio_to_sheets.py.
+package synch
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"math"
+	"strconv"
+	"strings"
+)
+
+// Transaction is the projection of a Fio transaction that participates
+// in the Sync ID hash. Other fields (ks, ss, sender_account, …) are
+// intentionally excluded — they are not part of the Python hash.
+//
+// Currency: leave "" to inherit the Python default of "CZK" (matches
+// the HTML scraper path which omits the key entirely).
+type Transaction struct {
+	Date     string
+	Amount   float64
+	Currency string
+	Sender   string
+	VS       string
+	Message  string
+	BankID   string
+}
+
+// GenerateSyncID returns the lowercase SHA-256 hex digest of
+// "date|amount|currency|sender|vs|message|bank_id" (lower-cased), used
+// as the dedup key in column K of the payments sheet.
+//
+// Byte-stable with scripts/sync_fio_to_sheets.py generate_sync_id.
+func GenerateSyncID(tx Transaction) string {
+	currency := tx.Currency
+	if currency == "" {
+		currency = "CZK"
+	}
+	raw := strings.ToLower(strings.Join([]string{
+		tx.Date,
+		formatAmount(tx.Amount),
+		currency,
+		tx.Sender,
+		tx.VS,
+		tx.Message,
+		tx.BankID,
+	}, "|"))
+	sum := sha256.Sum256([]byte(raw))
+	return hex.EncodeToString(sum[:])
+}
+
+// formatAmount mimics Python's str(float) for Fio transaction amounts.
+// Python uses decimal notation for abs(f) in [1e-4, 1e16) and scientific
+// notation outside that range, always adding ".0" to whole-valued decimals.
+func formatAmount(f float64) string {
+	abs := math.Abs(f)
+	if abs != 0 && (abs < 1e-4 || abs >= 1e16) {
+		return strconv.FormatFloat(f, 'e', -1, 64)
+	}
+	s := strconv.FormatFloat(f, 'f', -1, 64)
+	if !strings.ContainsRune(s, '.') {
+		s += ".0"
+	}
+	return s
+}

go/internal/domain/synch/synch_test.go

@@ -0,0 +1,119 @@
+package synch
+
+import (
+	"testing"
+)
+
+// All expected digests verified against the live Python implementation on 2026-05-06:
+//
+//	PYTHONPATH=scripts:. python -c '
+//	from sync_fio_to_sheets import generate_sync_id
+//	cases = [
+//	    {"date":"2026-01-15","amount":500.0,"currency":"CZK","sender":"Jan Novak","vs":"123","message":"clenske 1/2026","bank_id":"abc123"},
+//	    {"date":"2026-01-15","amount":500.0,"sender":"Jan Novak","vs":"123","message":"clenske 1/2026","bank_id":"abc123"},
+//	    {"date":"2026-02-10","amount":1234.56,"currency":"CZK","sender":"ABC SRO","vs":"","message":"FAKTURA 42","bank_id":"xyz"},
+//	    {"date":"2026-03-01","amount":-500.0,"currency":"CZK","sender":"refund","vs":"","message":"","bank_id":""},
+//	    {"date":"2026-04-01","amount":0.0,"currency":"CZK","sender":"","vs":"","message":"","bank_id":""},
+//	    {"date":"","amount":0.0,"currency":"CZK","sender":"","vs":"","message":"","bank_id":""},
+//	]
+//	for c in cases: print(generate_sync_id(c))
+//	'
+func TestGenerateSyncID(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		name string
+		tx   Transaction
+		want string
+	}{
+		{
+			name: "all fields set",
+			tx: Transaction{
+				Date: "2026-01-15", Amount: 500.0, Currency: "CZK",
+				Sender: "Jan Novak", VS: "123", Message: "clenske 1/2026", BankID: "abc123",
+			},
+			want: "4ac26598b6f23965380690172156a438a7e97a97dcedf222e5afe1afbe2c1bc4",
+		},
+		{
+			name: "currency empty defaults to CZK",
+			tx: Transaction{
+				Date: "2026-01-15", Amount: 500.0, Currency: "",
+				Sender: "Jan Novak", VS: "123", Message: "clenske 1/2026", BankID: "abc123",
+			},
+			want: "4ac26598b6f23965380690172156a438a7e97a97dcedf222e5afe1afbe2c1bc4",
+		},
+		{
+			name: "mixed-case fields lowercased before hashing",
+			tx: Transaction{
+				Date: "2026-02-10", Amount: 1234.56, Currency: "CZK",
+				Sender: "ABC SRO", VS: "", Message: "FAKTURA 42", BankID: "xyz",
+			},
+			want: "d40fa224d4fa572ffcd58e308e5c6508c4d5ca087b24ef6ff9284528fc128250",
+		},
+		{
+			name: "negative amount",
+			tx: Transaction{
+				Date: "2026-03-01", Amount: -500.0, Currency: "CZK",
+				Sender: "refund", VS: "", Message: "", BankID: "",
+			},
+			want: "0c630a407160367c396a2beec08efb94c319b4d84a8b90cc2be89e6ea10c391f",
+		},
+		{
+			name: "zero amount",
+			tx: Transaction{
+				Date: "2026-04-01", Amount: 0.0, Currency: "CZK",
+				Sender: "", VS: "", Message: "", BankID: "",
+			},
+			want: "6a23ce53717cd539064d550d2c2ec5de2e9bf81016d16852820ca9b8e259331f",
+		},
+		{
+			// Python equivalent: {"date":"","amount":0.0,"currency":"CZK","sender":"","vs":"","message":"","bank_id":""}
+			// Note: Python generate_sync_id({}) hashes "" for missing amount, not "0.0".
+			name: "zero-value Transaction",
+			tx:   Transaction{},
+			want: "d33d7e391f5a43f0192bb5a34c0ec15715139125678ecef8e1324af7d943b21d",
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := GenerateSyncID(tc.tx)
+			if got != tc.want {
+				t.Errorf("GenerateSyncID(%+v) = %q, want %q", tc.tx, got, tc.want)
+			}
+		})
+	}
+}
+
+// All expected strings verified against the live Python implementation on 2026-05-06:
+//
+//	PYTHONPATH=scripts:. python -c '
+//	for v in [0.0, 500.0, -500.0, 0.1, 1234.56, 99999.99, 1500000.0, 1e16, 1e-5]:
+//	    print(repr(v), "->", repr(str(v)))
+//	'
+func TestFormatAmount(t *testing.T) {
+	t.Parallel()
+
+	cases := []struct {
+		in   float64
+		want string
+	}{
+		{0.0, "0.0"},
+		{500.0, "500.0"},
+		{-500.0, "-500.0"},
+		{0.1, "0.1"},
+		{1234.56, "1234.56"},
+		{99999.99, "99999.99"},
+		{1500000.0, "1500000.0"},
+		{1e16, "1e+16"},
+		{1e-5, "1e-05"},
+	}
+
+	for _, tc := range cases {
+		got := formatAmount(tc.in)
+		if got != tc.want {
+			t.Errorf("formatAmount(%v) = %q, want %q", tc.in, got, tc.want)
+		}
+	}
+}

go/internal/io/attendance/client.go

@@ -0,0 +1,64 @@
+// Package attendance fetches attendance CSV exports from Google Sheets.
+// No auth required — the sheet must be publicly readable.
+package attendance
+
+import (
+	"context"
+	"encoding/csv"
+	"fmt"
+	"io"
+	"net/http"
+	"strings"
+)
+
+const exportBase = "https://docs.google.com/spreadsheets/d"
+
+// Client fetches attendance CSV exports from a public Google Spreadsheet.
+type Client struct {
+	http      *http.Client
+	sheetID   string
+	adultGID  string
+	juniorGID string
+}
+
+// New returns a Client for the given spreadsheet.
+// adultGID is typically "0"; juniorGID is the GID of the junior tab.
+func New(httpClient *http.Client, sheetID, adultGID, juniorGID string) *Client {
+	if httpClient == nil {
+		httpClient = http.DefaultClient
+	}
+	return &Client{http: httpClient, sheetID: sheetID, adultGID: adultGID, juniorGID: juniorGID}
+}
+
+// FetchAdults returns the adult attendance tab as raw CSV rows.
+func (c *Client) FetchAdults(ctx context.Context) ([][]string, error) {
+	return c.fetch(ctx, c.adultGID)
+}
+
+// FetchJuniors returns the junior attendance tab as raw CSV rows.
+func (c *Client) FetchJuniors(ctx context.Context) ([][]string, error) {
+	return c.fetch(ctx, c.juniorGID)
+}
+
+func (c *Client) fetch(ctx context.Context, gid string) ([][]string, error) {
+	url := fmt.Sprintf("%s/%s/export?format=csv&gid=%s", exportBase, c.sheetID, gid)
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := c.http.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("attendance fetch: HTTP %d for gid=%s", resp.StatusCode, gid)
+	}
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	r := csv.NewReader(strings.NewReader(string(body)))
+	r.FieldsPerRecord = -1 // rows may have different lengths
+	return r.ReadAll()
+}

go/internal/io/attendance/client_test.go

@@ -0,0 +1,93 @@
+package attendance
+
+import (
+	"context"
+	"encoding/csv"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestClientFetchAdults(t *testing.T) {
+	data, err := os.ReadFile("testdata/adults_minimal.csv")
+	if err != nil {
+		t.Fatal(err)
+	}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		_, _ = w.Write(data)
+	}))
+	defer srv.Close()
+
+	// Point the client at our test server by re-implementing fetch against its URL.
+	rows, err := fetchURL(context.Background(), srv.Client(), srv.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(rows) < 2 {
+		t.Fatalf("want ≥2 rows, got %d", len(rows))
+	}
+	if rows[0][0] != "Jméno" {
+		t.Errorf("unexpected header: %q", rows[0][0])
+	}
+}
+
+func TestFake(t *testing.T) {
+	adultRows := parseCSV(t, "testdata/adults_minimal.csv")
+	juniorRows := parseCSV(t, "testdata/juniors_minimal.csv")
+
+	f := &Fake{Adults: adultRows, Juniors: juniorRows}
+
+	got, err := f.FetchAdults(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got[0][0] != "Jméno" {
+		t.Errorf("adults header: %q", got[0][0])
+	}
+
+	got, err = f.FetchJuniors(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got[1][0] != "Junior One" {
+		t.Errorf("juniors first member: %q", got[1][0])
+	}
+}
+
+func parseCSV(t *testing.T, path string) [][]string {
+	t.Helper()
+	b, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	r := csv.NewReader(strings.NewReader(string(b)))
+	r.FieldsPerRecord = -1
+	rows, err := r.ReadAll()
+	if err != nil {
+		t.Fatal(err)
+	}
+	return rows
+}
+
+// fetchURL is a test helper that exercises the shared fetch logic against an arbitrary URL.
+func fetchURL(ctx context.Context, hc *http.Client, url string) ([][]string, error) {
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := hc.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	b, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	r := csv.NewReader(strings.NewReader(string(b)))
+	r.FieldsPerRecord = -1
+	return r.ReadAll()
+}

go/internal/io/attendance/fake.go

@@ -0,0 +1,12 @@
+package attendance
+
+import "context"
+
+// Fake is an in-memory replacement for Client, used in tests.
+type Fake struct {
+	Adults  [][]string
+	Juniors [][]string
+}
+
+func (f *Fake) FetchAdults(_ context.Context) ([][]string, error)  { return f.Adults, nil }
+func (f *Fake) FetchJuniors(_ context.Context) ([][]string, error) { return f.Juniors, nil }

go/internal/io/attendance/testdata/adults_minimal.csv

@@ -0,0 +1,4 @@
+Jméno,Tier,,,01.09.2025,08.09.2025,15.09.2025
+Member One,A,,,TRUE,TRUE,FALSE
+Member Two,A,,,TRUE,FALSE,FALSE
+# last line,,,,,

go/internal/io/attendance/testdata/juniors_minimal.csv

@@ -0,0 +1,4 @@
+Jméno,Tier,,,01.09.2025,08.09.2025,15.09.2025
+Junior One,J,,,TRUE,TRUE,TRUE
+# Trenéři,,,,,
+Coach One,X,,,FALSE,FALSE,FALSE

go/internal/io/cache/filecache.go

@@ -0,0 +1,209 @@
+// Package cache implements a Drive-modifiedTime-gated JSON file cache,
+// mirroring scripts/cache_utils.py.
+package cache
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"fuj-management/go/internal/io/drive"
+	"os"
+	"path/filepath"
+	"sync"
+	"time"
+)
+
+// DriveClient is the subset of drive.Client used by FileCache.
+type DriveClient interface {
+	ModifiedTime(ctx context.Context, fileID string) (string, error)
+}
+
+type cacheFile struct {
+	ModifiedTime string          `json:"modifiedTime"`
+	Data         json.RawMessage `json:"data"`
+	CachedAt     string          `json:"cachedAt"`
+}
+
+// FileCache wraps a Drive client to gate JSON file caching on sheet modifiedTime.
+//
+// Two TTL knobs mirror scripts/cache_utils.py:
+//   - ttl: if the cache file on disk is younger than this, skip the Drive check entirely.
+//   - apiCheckTTL: debounces in-memory Drive API calls per sheet ID.
+//
+// Atomic writes: data is marshaled to a .tmp file then os.Rename'd.
+// Cache files are compatible with Python's format:
+//
+//	{"modifiedTime":"…","data":…,"cachedAt":"…"}
+type FileCache struct {
+	drive       DriveClient
+	dir         string
+	sheetMap    map[string]string // cache key → Drive file ID
+	ttl         time.Duration
+	apiCheckTTL time.Duration
+	mu          sync.Mutex
+	lastChecked map[string]time.Time
+}
+
+// New creates a FileCache.
+// sheetMap maps cache keys to Google Sheets/Drive file IDs (mirrors CACHE_SHEET_MAP in config).
+func New(d DriveClient, dir string, sheetMap map[string]string, ttl, apiCheckTTL time.Duration) *FileCache {
+	return &FileCache{
+		drive:       d,
+		dir:         dir,
+		sheetMap:    sheetMap,
+		ttl:         ttl,
+		apiCheckTTL: apiCheckTTL,
+		lastChecked: make(map[string]time.Time),
+	}
+}
+
+// Get returns the cached value for cacheKey, calling fetch if the cache is stale.
+// T must be JSON-marshalable.
+func Get[T any](ctx context.Context, fc *FileCache, cacheKey string, fetch func(context.Context) (T, error)) (T, error) {
+	sheetID := fc.sheetMap[cacheKey]
+	if sheetID == "" {
+		sheetID = cacheKey
+	}
+	cacheFilePath := filepath.Join(fc.dir, cacheKey+"_cache.json")
+
+	currentModTime, err := fc.currentModifiedTime(ctx, sheetID, cacheFilePath)
+	if err != nil {
+		return *new(T), fmt.Errorf("cache: modifiedTime for %s: %w", cacheKey, err)
+	}
+
+	// Try cache hit
+	if data, ok := readCache[T](cacheFilePath, currentModTime); ok {
+		return data, nil
+	}
+
+	// Cache miss — fetch fresh data
+	fresh, err := fetch(ctx)
+	if err != nil {
+		return *new(T), err
+	}
+	if err := writeCache(cacheFilePath, currentModTime, fresh); err != nil {
+		// Non-fatal: log but don't fail the request
+		_, _ = fmt.Fprintf(os.Stderr, "cache: write %s: %v\n", cacheKey, err)
+	}
+	return fresh, nil
+}
+
+// Flush deletes all *_cache.json files in the cache dir and resets in-memory state.
+func (fc *FileCache) Flush() (int, error) {
+	fc.mu.Lock()
+	fc.lastChecked = make(map[string]time.Time)
+	fc.mu.Unlock()
+
+	pattern := filepath.Join(fc.dir, "*_cache.json")
+	matches, err := filepath.Glob(pattern)
+	if err != nil {
+		return 0, err
+	}
+	for _, f := range matches {
+		_ = os.Remove(f)
+	}
+	return len(matches), nil
+}
+
+// currentModifiedTime returns a stable string representing the current version
+// of the sheet, using the in-memory + file-mtime TTL guards before hitting Drive.
+// On Drive failure, falls back to a 5-minute bucket string (matching Python).
+func (fc *FileCache) currentModifiedTime(ctx context.Context, sheetID, cacheFilePath string) (string, error) {
+	now := time.Now()
+
+	fc.mu.Lock()
+	lastCheck := fc.lastChecked[sheetID]
+	fc.mu.Unlock()
+
+	// Guard 1: in-memory debounce — skip Drive if checked recently
+	if fc.apiCheckTTL > 0 && now.Sub(lastCheck) < fc.apiCheckTTL {
+		if mt, ok := readModifiedTime(cacheFilePath); ok {
+			return mt, nil
+		}
+	}
+
+	// Guard 2: cache file is young enough — trust the stored modifiedTime
+	if fc.ttl > 0 {
+		if info, err := os.Stat(cacheFilePath); err == nil {
+			if now.Sub(info.ModTime()) < fc.ttl {
+				if mt, ok := readModifiedTime(cacheFilePath); ok {
+					fc.mu.Lock()
+					fc.lastChecked[sheetID] = now
+					fc.mu.Unlock()
+					return mt, nil
+				}
+			}
+		}
+	}
+
+	// Hit Drive API
+	mt, err := fc.drive.ModifiedTime(ctx, sheetID)
+	if err != nil {
+		// Fallback: 5-minute bucket string, matches Python _fallback_ttl()
+		bucket := time.Now().Unix() / 300
+		return fmt.Sprintf("ttl-5m-%d", bucket), nil
+	}
+	fc.mu.Lock()
+	fc.lastChecked[sheetID] = now
+	fc.mu.Unlock()
+	return mt, nil
+}
+
+func readModifiedTime(path string) (string, bool) {
+	cf, ok := readCacheFile(path)
+	if !ok {
+		return "", false
+	}
+	return cf.ModifiedTime, cf.ModifiedTime != ""
+}
+
+func readCacheFile(path string) (cacheFile, bool) {
+	b, err := os.ReadFile(path)
+	if err != nil {
+		return cacheFile{}, false
+	}
+	var cf cacheFile
+	if err := json.Unmarshal(b, &cf); err != nil {
+		return cacheFile{}, false
+	}
+	return cf, true
+}
+
+func readCache[T any](path, currentModTime string) (T, bool) {
+	cf, ok := readCacheFile(path)
+	if !ok || cf.ModifiedTime != currentModTime {
+		return *new(T), false
+	}
+	var v T
+	if err := json.Unmarshal(cf.Data, &v); err != nil {
+		return *new(T), false
+	}
+	return v, true
+}
+
+func writeCache(path, modTime string, data any) error {
+	raw, err := json.Marshal(data)
+	if err != nil {
+		return err
+	}
+	cf := cacheFile{
+		ModifiedTime: modTime,
+		Data:         json.RawMessage(raw),
+		CachedAt:     time.Now().Format(time.RFC3339),
+	}
+	b, err := json.Marshal(cf)
+	if err != nil {
+		return err
+	}
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		return err
+	}
+	tmp := path + ".tmp"
+	if err := os.WriteFile(tmp, b, 0o600); err != nil {
+		return err
+	}
+	return os.Rename(tmp, path)
+}
+
+// Ensure *drive.Client satisfies DriveClient at compile time.
+var _ DriveClient = (*drive.Client)(nil)

go/internal/io/cache/filecache_test.go

@@ -0,0 +1,125 @@
+package cache
+
+import (
+	"context"
+	"errors"
+	"fuj-management/go/internal/io/drive"
+	"os"
+	"testing"
+	"time"
+)
+
+func TestGet_FreshFetch(t *testing.T) {
+	dir := t.TempDir()
+	d := &drive.Fake{Times: map[string]string{"sheet1": "2026-01-01T00:00:00Z"}}
+	fc := New(d, dir, map[string]string{"mykey": "sheet1"}, time.Minute, time.Minute)
+
+	calls := 0
+	got, err := Get(context.Background(), fc, "mykey", func(_ context.Context) ([]string, error) {
+		calls++
+		return []string{"a", "b"}, nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(got) != 2 || got[0] != "a" {
+		t.Errorf("unexpected: %v", got)
+	}
+	if calls != 1 {
+		t.Errorf("want 1 fetch call, got %d", calls)
+	}
+}
+
+func TestGet_CacheHit(t *testing.T) {
+	dir := t.TempDir()
+	d := &drive.Fake{Times: map[string]string{"sheet1": "2026-01-01T00:00:00Z"}}
+	fc := New(d, dir, map[string]string{"mykey": "sheet1"}, time.Minute, time.Minute)
+
+	fetch := func(_ context.Context) ([]string, error) { return []string{"a"}, nil }
+	if _, err := Get(context.Background(), fc, "mykey", fetch); err != nil {
+		t.Fatal(err)
+	}
+
+	// Second call — modifiedTime unchanged, should hit cache
+	calls := 0
+	got, err := Get(context.Background(), fc, "mykey", func(_ context.Context) ([]string, error) {
+		calls++
+		return []string{"SHOULD_NOT_CALL"}, nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got[0] != "a" {
+		t.Errorf("want cache hit with 'a', got %q", got[0])
+	}
+	if calls != 0 {
+		t.Errorf("want 0 fetch calls on hit, got %d", calls)
+	}
+}
+
+func TestGet_CacheMiss_OnModifiedTimeChange(t *testing.T) {
+	dir := t.TempDir()
+	d := &drive.Fake{Times: map[string]string{"sheet1": "2026-01-01T00:00:00Z"}}
+	// No TTL guards so we always hit Drive
+	fc := New(d, dir, map[string]string{"mykey": "sheet1"}, 0, 0)
+
+	fetch := func(_ context.Context) ([]string, error) { return []string{"v1"}, nil }
+	if _, err := Get(context.Background(), fc, "mykey", fetch); err != nil {
+		t.Fatal(err)
+	}
+
+	// Sheet updated — change modifiedTime
+	d.Times["sheet1"] = "2026-02-01T00:00:00Z"
+	got, err := Get(context.Background(), fc, "mykey", func(_ context.Context) ([]string, error) {
+		return []string{"v2"}, nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got[0] != "v2" {
+		t.Errorf("want v2 after sheet update, got %q", got[0])
+	}
+}
+
+func TestGet_DriveFailureFallback(t *testing.T) {
+	dir := t.TempDir()
+	d := &drive.Fake{Err: errors.New("drive down")}
+	fc := New(d, dir, nil, 0, 0)
+
+	calls := 0
+	_, err := Get(context.Background(), fc, "mykey", func(_ context.Context) ([]string, error) {
+		calls++
+		return []string{"fallback"}, nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if calls != 1 {
+		t.Errorf("want 1 fetch call, got %d", calls)
+	}
+}
+
+func TestFlush(t *testing.T) {
+	dir := t.TempDir()
+	d := &drive.Fake{Times: map[string]string{"sheet1": "t1"}}
+	fc := New(d, dir, map[string]string{"k": "sheet1"}, 0, 0)
+
+	if _, err := Get(context.Background(), fc, "k", func(_ context.Context) (int, error) { return 42, nil }); err != nil {
+		t.Fatal(err)
+	}
+
+	n, err := fc.Flush()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 1 {
+		t.Errorf("want 1 deleted file, got %d", n)
+	}
+	// Cache dir should be empty of _cache.json files
+	entries, _ := os.ReadDir(dir)
+	for _, e := range entries {
+		if e.Name() != "" {
+			t.Errorf("expected empty dir after flush, found %s", e.Name())
+		}
+	}
+}

go/internal/io/drive/client.go

@@ -0,0 +1,46 @@
+// Package drive provides a thin wrapper around the Google Drive v3 API,
+// used only to read modifiedTime for cache invalidation.
+package drive
+
+import (
+	"context"
+	"net/http"
+	"time"
+
+	"google.golang.org/api/drive/v3"
+	"google.golang.org/api/option"
+)
+
+// Client wraps the Drive v3 API, scoped to read-only modifiedTime checks.
+type Client struct {
+	svc *drive.Service
+}
+
+// New builds a Client using a service-account credentials file.
+// timeout applies to each Drive API call.
+func New(ctx context.Context, credentialsPath string, timeout time.Duration) (*Client, error) {
+	hc := &http.Client{Timeout: timeout}
+	svc, err := drive.NewService(ctx,
+		option.WithCredentialsFile(credentialsPath), //nolint:staticcheck
+		option.WithScopes(drive.DriveReadonlyScope),
+		option.WithHTTPClient(hc),
+	)
+	if err != nil {
+		return nil, err
+	}
+	return &Client{svc: svc}, nil
+}
+
+// ModifiedTime returns the RFC3339 modifiedTime for the given Drive file ID.
+// Returns ("", err) if the Drive API call fails.
+func (c *Client) ModifiedTime(ctx context.Context, fileID string) (string, error) {
+	meta, err := c.svc.Files.Get(fileID).
+		Fields("modifiedTime").
+		SupportsAllDrives(true).
+		Context(ctx).
+		Do()
+	if err != nil {
+		return "", err
+	}
+	return meta.ModifiedTime, nil
+}

go/internal/io/drive/fake.go

@@ -0,0 +1,18 @@
+package drive
+
+import "context"
+
+// Fake is an in-memory replacement for Client used in tests.
+type Fake struct {
+	// Times maps file ID → modifiedTime string returned by ModifiedTime.
+	Times map[string]string
+	// Err, if non-nil, is returned instead of looking up Times.
+	Err error
+}
+
+func (f *Fake) ModifiedTime(_ context.Context, fileID string) (string, error) {
+	if f.Err != nil {
+		return "", f.Err
+	}
+	return f.Times[fileID], nil
+}

go/internal/io/fio/api.go

@@ -0,0 +1,136 @@
+package fio
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"strings"
+	"time"
+)
+
+// httpDoer is the subset of *http.Client used by both Fio impls.
+type httpDoer interface {
+	Do(*http.Request) (*http.Response, error)
+}
+
+// apiClient fetches transactions from the Fio REST API (JSON).
+// Ports scripts/fio_utils.py fetch_transactions_api.
+type apiClient struct {
+	token string
+	hc    httpDoer
+}
+
+func (c *apiClient) FetchTransactions(ctx context.Context, from, to time.Time) ([]Transaction, error) {
+	const layout = "2006-01-02"
+	url := fmt.Sprintf("https://fioapi.fio.cz/v1/rest/periods/%s/%s/%s/transactions.json",
+		c.token, from.Format(layout), to.Format(layout))
+	slog.Debug("fio api: GET",
+		"url", strings.Replace(url, c.token, "****", 1),
+		"from", from.Format(layout), "to", to.Format(layout))
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := c.hc.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	slog.Debug("fio api: response", "status", resp.StatusCode)
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("fio api: HTTP %d", resp.StatusCode)
+	}
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	txns, err := parseAPIResponse(body)
+	slog.Debug("fio api: parsed", "body_bytes", len(body), "parsed_count", len(txns))
+	return txns, err
+}
+
+// fioAPIResponse is the top-level envelope from the Fio JSON API.
+type fioAPIResponse struct {
+	AccountStatement struct {
+		TransactionList struct {
+			Transaction []map[string]json.RawMessage `json:"transaction"`
+		} `json:"transactionList"`
+	} `json:"accountStatement"`
+}
+
+func parseAPIResponse(body []byte) ([]Transaction, error) {
+	var resp fioAPIResponse
+	if err := json.Unmarshal(body, &resp); err != nil {
+		return nil, fmt.Errorf("fio api: parse JSON: %w", err)
+	}
+
+	var txns []Transaction
+	for _, raw := range resp.AccountStatement.TransactionList.Transaction {
+		amount := colFloat(raw, "column1")
+		if amount <= 0 {
+			continue // skip outgoing
+		}
+		dateRaw := colString(raw, "column0")
+		dateStr := ""
+		if len(dateRaw) >= 10 {
+			dateStr = dateRaw[:10]
+		}
+		txns = append(txns, Transaction{
+			Date:          dateStr,
+			Amount:        amount,
+			Sender:        colString(raw, "column10"),
+			Message:       colString(raw, "column16"),
+			VS:            colString(raw, "column5"),
+			KS:            colString(raw, "column4"),
+			SS:            colString(raw, "column6"),
+			UserID:        colString(raw, "column7"),
+			SenderAccount: colString(raw, "column2"),
+			BankID:        colString(raw, "column22"),
+			Currency:      colStringOr(raw, "column14", "CZK"),
+		})
+	}
+	return txns, nil
+}
+
+// colString extracts {"value":…} as a string from a column map.
+func colString(m map[string]json.RawMessage, col string) string {
+	raw, ok := m[col]
+	if !ok {
+		return ""
+	}
+	var cell struct {
+		Value *string `json:"value"`
+	}
+	if json.Unmarshal(raw, &cell) != nil || cell.Value == nil {
+		return ""
+	}
+	return *cell.Value
+}
+
+// colStringOr is colString with a fallback value.
+func colStringOr(m map[string]json.RawMessage, col, fallback string) string {
+	if v := colString(m, col); v != "" {
+		return v
+	}
+	return fallback
+}
+
+// colFloat extracts {"value":…} as a float64 from a column map.
+// Returns 0 on any error (null column, non-numeric value).
+func colFloat(m map[string]json.RawMessage, col string) float64 {
+	raw, ok := m[col]
+	if !ok {
+		return 0
+	}
+	var cell struct {
+		Value *float64 `json:"value"`
+	}
+	if json.Unmarshal(raw, &cell) != nil || cell.Value == nil {
+		return 0
+	}
+	return *cell.Value
+}

go/internal/io/fio/client.go

@@ -0,0 +1,45 @@
+// Package fio fetches Fio bank transactions via the JSON API or the
+// transparent-page HTML scraper, behind a common Client interface.
+package fio
+
+import (
+	"context"
+	"log/slog"
+	"net/http"
+	"time"
+)
+
+// Transaction is one incoming bank payment. Fields absent from the HTML scraper
+// (BankID, Currency, UserID, SenderAccount) are empty strings on that path.
+type Transaction struct {
+	Date          string
+	Amount        float64
+	Sender        string
+	Message       string
+	VS            string
+	KS            string
+	SS            string
+	UserID        string // column7; empty on HTML path
+	SenderAccount string // column2; empty on HTML path
+	BankID        string // column22; empty on HTML path
+	Currency      string // column14; empty on HTML path (assume CZK)
+}
+
+// Client fetches transactions for a date window.
+type Client interface {
+	FetchTransactions(ctx context.Context, from, to time.Time) ([]Transaction, error)
+}
+
+// New returns an apiClient when token is non-empty, otherwise a transparentClient.
+// hc may be nil, in which case http.DefaultClient is used.
+func New(token, accountNum string, hc httpDoer) Client {
+	if hc == nil {
+		hc = http.DefaultClient
+	}
+	if token != "" {
+		slog.Debug("fio: client selected", "type", "api")
+		return &apiClient{token: token, hc: hc}
+	}
+	slog.Debug("fio: client selected", "type", "transparent", "account_num", accountNum)
+	return &transparentClient{accountNum: accountNum, hc: hc}
+}

go/internal/io/fio/fake.go

@@ -0,0 +1,19 @@
+package fio
+
+import (
+	"context"
+	"time"
+)
+
+// Fake is an in-memory replacement for Client, used in tests.
+type Fake struct {
+	Transactions []Transaction
+	Err          error
+}
+
+func (f *Fake) FetchTransactions(_ context.Context, _, _ time.Time) ([]Transaction, error) {
+	if f.Err != nil {
+		return nil, f.Err
+	}
+	return f.Transactions, nil
+}

go/internal/io/fio/fio_test.go

@@ -0,0 +1,178 @@
+package fio
+
+import (
+	"context"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"testing"
+	"time"
+)
+
+func TestAPIClient_ParseResponse(t *testing.T) {
+	body, err := os.ReadFile("testdata/api_response.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	txns, err := parseAPIResponse(body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(txns) != 1 {
+		t.Fatalf("want 1 txn (outgoing filtered), got %d", len(txns))
+	}
+	tx := txns[0]
+	if tx.Date != "2026-04-10" {
+		t.Errorf("date: want '2026-04-10', got %q", tx.Date)
+	}
+	if tx.Amount != 750 {
+		t.Errorf("amount: want 750, got %v", tx.Amount)
+	}
+	if tx.Sender != "Jana Novakova" {
+		t.Errorf("sender: want 'Jana Novakova', got %q", tx.Sender)
+	}
+	if tx.Message != "duben 2026" {
+		t.Errorf("message: want 'duben 2026', got %q", tx.Message)
+	}
+	if tx.VS != "123" {
+		t.Errorf("vs: want '123', got %q", tx.VS)
+	}
+	if tx.BankID != "12345678901" {
+		t.Errorf("bank_id: want '12345678901', got %q", tx.BankID)
+	}
+}
+
+func TestAPIClient_HTTPRoundTrip(t *testing.T) {
+	body, _ := os.ReadFile("testdata/api_response.json")
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
+		_, _ = w.Write(body)
+	}))
+	defer srv.Close()
+
+	c := &apiClient{token: "TESTTOKEN", hc: &overrideClient{base: srv.Client(), baseURL: srv.URL}}
+	txns, err := c.FetchTransactions(context.Background(), time.Now().AddDate(0, -1, 0), time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(txns) != 1 {
+		t.Fatalf("want 1 txn, got %d", len(txns))
+	}
+}
+
+func TestTransparentClient_ParseHTML(t *testing.T) {
+	body, err := os.ReadFile("testdata/transparent.html")
+	if err != nil {
+		t.Fatal(err)
+	}
+	txns, err := parseTransparentHTML(body)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Only the incoming row (750 CZK) should be kept; -200 is outgoing
+	if len(txns) != 1 {
+		t.Fatalf("want 1 txn (outgoing filtered), got %d", len(txns))
+	}
+	tx := txns[0]
+	if tx.Date != "2026-04-10" {
+		t.Errorf("date: want '2026-04-10', got %q", tx.Date)
+	}
+	if tx.Amount != 750 {
+		t.Errorf("amount: want 750, got %v", tx.Amount)
+	}
+	if tx.Sender != "Jana Novakova" {
+		t.Errorf("sender: want 'Jana Novakova', got %q", tx.Sender)
+	}
+	if tx.VS != "123" {
+		t.Errorf("vs: want '123', got %q", tx.VS)
+	}
+	if tx.BankID != "" {
+		t.Errorf("bank_id: want empty on HTML path, got %q", tx.BankID)
+	}
+}
+
+func TestParseCzechDate(t *testing.T) {
+	cases := []struct{ in, want string }{
+		{"10.04.2026", "2026-04-10"},
+		{"10/04/2026", "2026-04-10"},
+		{"7.5.2026", "2026-05-07"},  // non-padded — real Fio transparent page format
+		{"3.12.2025", "2025-12-03"}, // non-padded single-digit day, double-digit month
+		{"07.05.26", "2026-05-07"},  // padded 2-digit year — current Fio transparent page format
+		{"7.5.26", "2026-05-07"},    // non-padded 2-digit year
+		{"07/05/26", "2026-05-07"},  // slash variant
+		{"", ""},
+		{"invalid", ""},
+	}
+	for _, c := range cases {
+		if got := parseCzechDate(c.in); got != c.want {
+			t.Errorf("parseCzechDate(%q) = %q, want %q", c.in, got, c.want)
+		}
+	}
+}
+
+func TestExtractSecondTableRows_NestedTable(t *testing.T) {
+	// Regression: a nested <table> inside the target must not cause early exit.
+	html := `<table class="table"><tr><td>nav</td></tr></table>
+<table class="table">
+  <thead><tr><th>Date</th></tr></thead>
+  <tbody>
+    <tr><td>7.5.2026</td><td><table><tr><td>nested</td></tr></table></td></tr>
+    <tr><td>6.5.2026</td><td></td></tr>
+  </tbody>
+</table>`
+	rows := extractSecondTableRows([]byte(html))
+	if len(rows) != 2 {
+		t.Errorf("want 2 data rows, got %d: %v", len(rows), rows)
+	}
+}
+
+func TestParseCzechAmount(t *testing.T) {
+	cases := []struct {
+		in   string
+		want float64
+	}{
+		{"750,00 CZK", 750},
+		{"1.500,00", 1500},
+		{"1500.00", 1500},
+		{"-200,00 CZK", -200},
+	}
+	for _, c := range cases {
+		if got := parseCzechAmount(c.in); got != c.want {
+			t.Errorf("parseCzechAmount(%q) = %v, want %v", c.in, got, c.want)
+		}
+	}
+}
+
+func TestFake(t *testing.T) {
+	f := &Fake{Transactions: []Transaction{{Date: "2026-04-01", Amount: 500}}}
+	txns, err := f.FetchTransactions(context.Background(), time.Now(), time.Now())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(txns) != 1 || txns[0].Date != "2026-04-01" {
+		t.Errorf("unexpected: %v", txns)
+	}
+}
+
+// overrideClient replaces the URL in requests so we can hit a local test server
+// instead of the real Fio URL.
+type overrideClient struct {
+	base    *http.Client
+	baseURL string
+}
+
+func (o *overrideClient) Do(req *http.Request) (*http.Response, error) {
+	r2, _ := http.NewRequestWithContext(req.Context(), req.Method, o.baseURL+req.URL.Path, nil)
+	resp, err := o.base.Do(r2)
+	if err != nil {
+		return nil, err
+	}
+	// The api client reads the body, so re-serve whatever the test server returned.
+	return resp, nil
+}
+
+// verify Fake satisfies Client
+var _ Client = (*Fake)(nil)
+
+// ensure io.ReadAll isn't called at top level (compile-time reference suppressor)
+var _ = io.ReadAll

go/internal/io/fio/testdata/api_response.json

@@ -0,0 +1,29 @@
+{
+  "accountStatement": {
+    "transactionList": {
+      "transaction": [
+        {
+          "column0": {"value": "2026-04-10+0200", "name": "Datum", "id": 0},
+          "column1": {"value": 750.0, "name": "Objem", "id": 1},
+          "column2": {"value": "123456789/0300", "name": "Protiúčet", "id": 2},
+          "column4": {"value": "0308", "name": "KS", "id": 4},
+          "column5": {"value": "123", "name": "VS", "id": 5},
+          "column6": {"value": "", "name": "SS", "id": 6},
+          "column7": {"value": "Jana Nováková", "name": "Uživatelská identifikace", "id": 7},
+          "column10": {"value": "Jana Novakova", "name": "Název protiúčtu", "id": 10},
+          "column14": {"value": "CZK", "name": "Měna", "id": 14},
+          "column16": {"value": "duben 2026", "name": "Zpráva pro příjemce", "id": 16},
+          "column22": {"value": "12345678901", "name": "ID operace", "id": 22}
+        },
+        {
+          "column0": {"value": "2026-04-11+0200", "name": "Datum", "id": 0},
+          "column1": {"value": -200.0, "name": "Objem", "id": 1},
+          "column10": {"value": "Outgoing", "name": "Název protiúčtu", "id": 10},
+          "column14": {"value": "CZK", "name": "Měna", "id": 14},
+          "column16": {"value": "", "name": "Zpráva pro příjemce", "id": 16},
+          "column22": {"value": "99999999999", "name": "ID operace", "id": 22}
+        }
+      ]
+    }
+  }
+}

go/internal/io/fio/testdata/transparent.html

@@ -0,0 +1,37 @@
+<!DOCTYPE html>
+<html>
+<body>
+<!-- First table (ignored) -->
+<table class="table"><tr><td>ignored</td></tr></table>
+<!-- Second table (target) -->
+<table class="table">
+  <thead>
+    <tr><th>Datum</th><th>Částka</th><th>Typ</th><th>Název protiúčtu</th><th>Zpráva</th><th>KS</th><th>VS</th><th>SS</th><th>Poznámka</th></tr>
+  </thead>
+  <tbody>
+    <tr>
+      <td>10.04.2026</td>
+      <td>750,00&nbsp;CZK</td>
+      <td>Příjem</td>
+      <td>Jana Novakova</td>
+      <td>duben 2026</td>
+      <td>0308</td>
+      <td>123</td>
+      <td></td>
+      <td></td>
+    </tr>
+    <tr>
+      <td>09.04.2026</td>
+      <td>-200,00&nbsp;CZK</td>
+      <td>Odchozí</td>
+      <td>Someone</td>
+      <td>outgoing</td>
+      <td></td>
+      <td></td>
+      <td></td>
+      <td></td>
+    </tr>
+  </tbody>
+</table>
+</body>
+</html>

go/internal/io/fio/transparent.go

@@ -0,0 +1,247 @@
+package fio
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"log/slog"
+	"net/http"
+	"regexp"
+	"strings"
+	"time"
+	"unicode"
+
+	ghtml "golang.org/x/net/html"
+)
+
+// transparentClient fetches transactions from the Fio transparent account page (HTML).
+// Ports scripts/fio_utils.py FioTableParser + fetch_transactions_transparent.
+type transparentClient struct {
+	accountNum string
+	hc         httpDoer
+}
+
+func (c *transparentClient) FetchTransactions(ctx context.Context, from, to time.Time) ([]Transaction, error) {
+	// Transparent page date format: D.M.YYYY
+	url := fmt.Sprintf(
+		"https://ib.fio.cz/ib/transparent?a=%s&f=%s&t=%s",
+		c.accountNum,
+		from.Format("2.1.2006"),
+		to.Format("2.1.2006"),
+	)
+	slog.Debug("fio transparent: GET",
+		"url", url,
+		"from", from.Format("2006-01-02"), "to", to.Format("2006-01-02"))
+
+	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return nil, err
+	}
+	resp, err := c.hc.Do(req)
+	if err != nil {
+		return nil, err
+	}
+	defer resp.Body.Close()
+	slog.Debug("fio transparent: response", "status", resp.StatusCode)
+	if resp.StatusCode != http.StatusOK {
+		return nil, fmt.Errorf("fio transparent: HTTP %d", resp.StatusCode)
+	}
+	body, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return nil, err
+	}
+	slog.Debug("fio transparent: body read", "body_bytes", len(body))
+	return parseTransparentHTML(body)
+}
+
+// Column indices in the transparent-page table (0-based).
+// Datum | Částka | Typ | Název protiúčtu | Zpráva pro příjemce | KS | VS | SS | Poznámka
+const (
+	tColDate    = 0
+	tColAmount  = 1
+	tColSender  = 3
+	tColMessage = 4
+	tColKS      = 5
+	tColVS      = 6
+	tColSS      = 7
+)
+
+func parseTransparentHTML(body []byte) ([]Transaction, error) {
+	rows := extractSecondTableRows(body)
+
+	var txns []Transaction
+	var droppedBadDate, droppedNonpositive int
+	for _, row := range rows {
+		col := func(i int) string {
+			if i < len(row) {
+				return strings.TrimSpace(row[i])
+			}
+			return ""
+		}
+		dateStr := parseCzechDate(col(tColDate))
+		amount := parseCzechAmount(col(tColAmount))
+		if dateStr == "" {
+			droppedBadDate++
+			continue
+		}
+		if amount <= 0 {
+			droppedNonpositive++
+			continue
+		}
+		txns = append(txns, Transaction{
+			Date:    dateStr,
+			Amount:  amount,
+			Sender:  col(tColSender),
+			Message: col(tColMessage),
+			KS:      col(tColKS),
+			VS:      col(tColVS),
+			SS:      col(tColSS),
+			BankID:  "", // not available on HTML path
+		})
+	}
+	slog.Debug("fio transparent: parsed",
+		"raw_rows", len(rows),
+		"kept", len(txns),
+		"dropped_bad_date", droppedBadDate,
+		"dropped_nonpositive_amount", droppedNonpositive)
+	return txns, nil
+}
+
+// extractSecondTableRows walks the HTML token stream and returns data rows
+// from the second <table class="table"> element, skipping the <thead>.
+// It tracks nesting depth so that nested <table> elements inside the target
+// do not trigger an early exit.
+func extractSecondTableRows(body []byte) [][]string {
+	z := ghtml.NewTokenizer(strings.NewReader(string(body)))
+
+	tableCount := 0
+	targetDepth := 0 // >0 while inside the target table (handles nesting)
+	inThead := false
+	inRow := false
+	inCell := false
+	var currentRow []string
+	var cellBuf strings.Builder
+	var rows [][]string
+
+	for {
+		tt := z.Next()
+		if tt == ghtml.ErrorToken {
+			break
+		}
+		switch tt {
+		case ghtml.StartTagToken:
+			t := z.Token()
+			switch t.Data {
+			case "table":
+				if targetDepth > 0 {
+					targetDepth++ // nested table inside target; track so </table> doesn't exit early
+				} else if hasClass(t, "table") {
+					tableCount++
+					if tableCount == 2 {
+						targetDepth = 1
+					}
+				}
+			case "thead":
+				if targetDepth > 0 {
+					inThead = true
+				}
+			case "tr":
+				if targetDepth > 0 && !inThead {
+					inRow = true
+					currentRow = nil
+				}
+			case "td", "th":
+				if inRow {
+					inCell = true
+					cellBuf.Reset()
+				}
+			}
+		case ghtml.EndTagToken:
+			t := z.Token()
+			switch t.Data {
+			case "td", "th":
+				if inCell {
+					currentRow = append(currentRow, cellBuf.String())
+					inCell = false
+				}
+			case "thead":
+				inThead = false
+			case "tr":
+				if inRow {
+					if len(currentRow) > 0 {
+						rows = append(rows, currentRow)
+					}
+					inRow = false
+				}
+			case "table":
+				if targetDepth > 0 {
+					targetDepth--
+					if targetDepth == 0 {
+						return rows
+					}
+				}
+			}
+		case ghtml.TextToken:
+			if inCell {
+				cellBuf.WriteString(z.Token().Data)
+			}
+		}
+	}
+	return rows
+}
+
+func hasClass(t ghtml.Token, cls string) bool {
+	for _, a := range t.Attr {
+		if a.Key == "class" {
+			for _, c := range strings.Fields(a.Val) {
+				if c == cls {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+// parseCzechDate parses Czech date strings → "YYYY-MM-DD".
+// Handles both zero-padded ("07.05.2026") and non-padded ("7.5.2026") variants
+// with dot or slash separators, as the Fio transparent page omits leading zeros.
+// Returns "" on parse error.
+func parseCzechDate(s string) string {
+	s = strings.TrimSpace(s)
+	for _, layout := range []string{
+		"2.1.2006", "02.01.2006", "2/1/2006", "02/01/2006",
+		"2.1.06", "02.01.06", "2/1/06", "02/01/06",
+	} {
+		if t, err := time.Parse(layout, s); err == nil {
+			return t.Format("2006-01-02")
+		}
+	}
+	return ""
+}
+
+var nonNumericRe = regexp.MustCompile(`[^\d.,]`)
+
+// parseCzechAmount parses "1 500,00 CZK" / "1.500,00" / "1500.00" → float64.
+// Returns 0 on error.
+func parseCzechAmount(s string) float64 {
+	// Remove NBSP, regular spaces, currency letters
+	s = strings.Map(func(r rune) rune {
+		if r == ' ' || unicode.IsSpace(r) || unicode.IsLetter(r) {
+			return -1
+		}
+		return r
+	}, s)
+
+	if strings.Contains(s, ",") {
+		// Czech decimal: 1.500,00 → remove dots (thousand sep), comma → dot
+		s = strings.ReplaceAll(s, ".", "")
+		s = strings.ReplaceAll(s, ",", ".")
+	} else {
+		// Remove any remaining non-numeric except one dot
+		s = nonNumericRe.ReplaceAllString(s, "")
+	}
+	var f float64
+	_, _ = fmt.Sscanf(s, "%f", &f)
+	return f
+}

go/internal/io/sheets/client.go

@@ -0,0 +1,124 @@
+// Package sheets provides a typed wrapper around the Google Sheets v4 API.
+package sheets
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"google.golang.org/api/option"
+	sheetsv4 "google.golang.org/api/sheets/v4"
+)
+
+// ValueRange pairs an R1C1 range with its cell values, used for batchUpdate.
+type ValueRange struct {
+	Range  string  // R1C1 notation, e.g. "R2C4:R2C6"
+	Values [][]any // one sub-slice per row
+}
+
+// Client wraps the Sheets v4 API with the operations needed by this project.
+type Client struct {
+	svc *sheetsv4.Service
+}
+
+// New builds a Client using a service-account credentials file.
+func New(ctx context.Context, credentialsPath string, _ time.Duration) (*Client, error) {
+	svc, err := sheetsv4.NewService(ctx,
+		option.WithCredentialsFile(credentialsPath), //nolint:staticcheck
+		option.WithScopes(sheetsv4.SpreadsheetsScope),
+	)
+	if err != nil {
+		return nil, err
+	}
+	return &Client{svc: svc}, nil
+}
+
+// GetValues fetches a range from a spreadsheet with UNFORMATTED_VALUE rendering
+// (numbers as numbers, dates as serial floats — matching Python's behaviour).
+func (c *Client) GetValues(ctx context.Context, spreadsheetID, a1Range string) ([][]any, error) {
+	resp, err := c.svc.Spreadsheets.Values.
+		Get(spreadsheetID, a1Range).
+		ValueRenderOption("UNFORMATTED_VALUE").
+		Context(ctx).
+		Do()
+	if err != nil {
+		return nil, err
+	}
+	rows := make([][]any, len(resp.Values))
+	copy(rows, resp.Values)
+	return rows, nil
+}
+
+// AppendValues appends rows to the first empty row after a1Range.
+func (c *Client) AppendValues(ctx context.Context, spreadsheetID, a1Range string, rows [][]any) error {
+	vals := make([][]any, len(rows))
+	copy(vals, rows)
+	_, err := c.svc.Spreadsheets.Values.
+		Append(spreadsheetID, a1Range, &sheetsv4.ValueRange{Values: vals}).
+		ValueInputOption("USER_ENTERED").
+		Context(ctx).
+		Do()
+	return err
+}
+
+// BatchUpdateValues writes multiple non-contiguous ranges in one API call.
+func (c *Client) BatchUpdateValues(ctx context.Context, spreadsheetID string, updates []ValueRange) error {
+	data := make([]*sheetsv4.ValueRange, len(updates))
+	for i, u := range updates {
+		vals := make([][]any, len(u.Values))
+		copy(vals, u.Values)
+		data[i] = &sheetsv4.ValueRange{Range: u.Range, Values: vals}
+	}
+	_, err := c.svc.Spreadsheets.Values.
+		BatchUpdate(spreadsheetID, &sheetsv4.BatchUpdateValuesRequest{
+			ValueInputOption: "USER_ENTERED",
+			Data:             data,
+		}).
+		Context(ctx).
+		Do()
+	return err
+}
+
+// WriteHeader overwrites row 1 of the spreadsheet with the given labels.
+func (c *Client) WriteHeader(ctx context.Context, spreadsheetID string, labels []string) error {
+	row := make([]any, len(labels))
+	for i, l := range labels {
+		row[i] = l
+	}
+	_, err := c.svc.Spreadsheets.Values.
+		Update(spreadsheetID, "A1", &sheetsv4.ValueRange{Values: [][]any{row}}).
+		ValueInputOption("USER_ENTERED").
+		Context(ctx).
+		Do()
+	return err
+}
+
+// SortByDateColumn sorts rows 2..10000 of the first sheet ascending by column A (Date).
+// Looks up the sheetId (gid) from spreadsheet metadata.
+func (c *Client) SortByDateColumn(ctx context.Context, spreadsheetID string) error {
+	meta, err := c.svc.Spreadsheets.Get(spreadsheetID).Context(ctx).Do()
+	if err != nil {
+		return fmt.Errorf("sheets: get spreadsheet: %w", err)
+	}
+	if len(meta.Sheets) == 0 {
+		return fmt.Errorf("sheets: spreadsheet has no sheets")
+	}
+	sheetID := meta.Sheets[0].Properties.SheetId
+
+	_, err = c.svc.Spreadsheets.BatchUpdate(spreadsheetID, &sheetsv4.BatchUpdateSpreadsheetRequest{
+		Requests: []*sheetsv4.Request{{
+			SortRange: &sheetsv4.SortRangeRequest{
+				Range: &sheetsv4.GridRange{
+					SheetId:       sheetID,
+					StartRowIndex: 1,
+					EndRowIndex:   10000,
+				},
+				SortSpecs: []*sheetsv4.SortSpec{{
+					DimensionIndex: 0,
+					SortOrder:      "ASCENDING",
+				}},
+			},
+		}},
+	}).Context(ctx).Do()
+	return err
+}

go/internal/io/sheets/fake.go

@@ -0,0 +1,53 @@
+package sheets
+
+import (
+	"context"
+	"fmt"
+)
+
+// Fake is an in-memory replacement for Client used in tests.
+// Values maps a "<spreadsheetID>/<a1Range>" key to pre-seeded rows.
+type Fake struct {
+	// Values maps "spreadsheetID/range" → rows returned by GetValues.
+	Values map[string][][]any
+	// Appended collects rows passed to AppendValues for assertion.
+	Appended []AppendCall
+	// BatchUpdated collects calls to BatchUpdateValues.
+	BatchUpdated []BatchCall
+}
+
+// AppendCall records one AppendValues invocation.
+type AppendCall struct {
+	SpreadsheetID string
+	Range         string
+	Rows          [][]any
+}
+
+// BatchCall records one BatchUpdateValues invocation.
+type BatchCall struct {
+	SpreadsheetID string
+	Updates       []ValueRange
+}
+
+func (f *Fake) GetValues(_ context.Context, spreadsheetID, a1Range string) ([][]any, error) {
+	key := spreadsheetID + "/" + a1Range
+	rows, ok := f.Values[key]
+	if !ok {
+		return nil, fmt.Errorf("sheets fake: no seed for %q", key)
+	}
+	return rows, nil
+}
+
+func (f *Fake) AppendValues(_ context.Context, spreadsheetID, a1Range string, rows [][]any) error {
+	f.Appended = append(f.Appended, AppendCall{SpreadsheetID: spreadsheetID, Range: a1Range, Rows: rows})
+	return nil
+}
+
+func (f *Fake) BatchUpdateValues(_ context.Context, spreadsheetID string, updates []ValueRange) error {
+	f.BatchUpdated = append(f.BatchUpdated, BatchCall{SpreadsheetID: spreadsheetID, Updates: updates})
+	return nil
+}
+
+func (f *Fake) WriteHeader(_ context.Context, _ string, _ []string) error { return nil }
+
+func (f *Fake) SortByDateColumn(_ context.Context, _ string) error { return nil }

go/internal/services/banksync/fio_table.go

@@ -0,0 +1,31 @@
+package banksync
+
+import (
+	"fmt"
+	"fuj-management/go/internal/io/fio"
+	"io"
+	"text/tabwriter"
+)
+
+func printFioTable(w io.Writer, txns []fio.Transaction, syncIDs []string, existing map[string]bool) {
+	tw := tabwriter.NewWriter(w, 0, 0, 2, ' ', 0)
+	fmt.Fprintln(tw, "DATE\tAMOUNT\tSENDER\tVS\tMESSAGE\tBANKID\tSTATUS")
+	for i, tx := range txns {
+		status := "NEW"
+		if existing[syncIDs[i]] {
+			status = "DUP"
+		}
+		fmt.Fprintf(tw, "%s\t%.2f\t%s\t%s\t%s\t%s\t%s\n",
+			tx.Date, tx.Amount, tx.Sender, tx.VS,
+			truncRunes(tx.Message, 40), tx.BankID, status)
+	}
+	_ = tw.Flush()
+}
+
+func truncRunes(s string, n int) string {
+	rs := []rune(s)
+	if len(rs) <= n {
+		return s
+	}
+	return string(rs[:n-1]) + "…"
+}

go/internal/services/banksync/infer.go

@@ -0,0 +1,170 @@
+package banksync
+
+import (
+	"context"
+	"fmt"
+	"fuj-management/go/internal/domain/matching"
+	"fuj-management/go/internal/domain/reconcile"
+	"fuj-management/go/internal/io/sheets"
+	"strings"
+	"time"
+)
+
+// InferOpts controls infer behaviour.
+type InferOpts struct {
+	DryRun bool // print planned updates without writing to the sheet
+}
+
+// AttendanceSource can load both adult and junior member lists.
+type AttendanceSource interface {
+	LoadAdults(ctx context.Context) ([]reconcile.Member, []string, error)
+	LoadJuniors(ctx context.Context) ([]reconcile.Member, []string, error)
+}
+
+// sheetReadWriter is the subset of *sheets.Client used by InferPayments.
+type sheetReadWriter interface {
+	GetValues(ctx context.Context, spreadsheetID, a1Range string) ([][]any, error)
+	BatchUpdateValues(ctx context.Context, spreadsheetID string, updates []sheets.ValueRange) error
+}
+
+// InferPayments fills empty Person/Purpose/Inferred Amount cells in the payments
+// sheet using name and month matching against the member list.
+// Returns the number of rows updated (or that would be updated on dry-run).
+// Ports scripts/infer_payments.py infer_payments.
+func InferPayments(
+	ctx context.Context,
+	spreadsheetID string,
+	sh sheetReadWriter,
+	attendance AttendanceSource,
+	opts InferOpts,
+) (int, error) {
+	rows, err := sh.GetValues(ctx, spreadsheetID, "A1:Z")
+	if err != nil {
+		return 0, fmt.Errorf("infer: read sheet: %w", err)
+	}
+	if len(rows) == 0 {
+		return 0, nil
+	}
+
+	header := rows[0]
+	colIdx := func(label string) int {
+		label = strings.ToLower(strings.TrimSpace(label))
+		for i, h := range header {
+			if strings.ToLower(strings.TrimSpace(fmt.Sprint(h))) == label {
+				return i
+			}
+		}
+		return -1
+	}
+
+	idxDate := colIdx("date")
+	idxAmount := colIdx("amount")
+	idxSender := colIdx("sender")
+	idxMessage := colIdx("message")
+	idxVS := colIdx("vs")
+	idxManual := colIdx("manual fix")
+	idxPerson := colIdx("person")
+	idxPurpose := colIdx("purpose")
+	idxInferred := colIdx("inferred amount")
+
+	for _, req := range []string{"person", "purpose", "inferred amount"} {
+		if colIdx(req) == -1 {
+			return 0, fmt.Errorf("infer: required column %q not found in sheet", req)
+		}
+	}
+
+	// Build union member list: adults + juniors, deduped by canonical key.
+	adults, _, err := attendance.LoadAdults(ctx)
+	if err != nil {
+		return 0, fmt.Errorf("infer: load adults: %w", err)
+	}
+	juniors, _, err := attendance.LoadJuniors(ctx)
+	if err != nil {
+		return 0, fmt.Errorf("infer: load juniors: %w", err)
+	}
+	memberNames := dedupeMembers(append(adults, juniors...))
+
+	defaultYear := time.Now().Year()
+
+	var updates []sheets.ValueRange
+	for i, row := range rows[1:] {
+		rowNum := i + 2 // 1-based, skip header
+
+		get := func(idx int) string {
+			if idx < 0 || idx >= len(row) {
+				return ""
+			}
+			return strings.TrimSpace(fmt.Sprint(row[idx]))
+		}
+
+		// Skip rule: any of manual fix / Person / Purpose non-empty → leave alone
+		if get(idxManual) != "" || get(idxPerson) != "" || get(idxPurpose) != "" {
+			continue
+		}
+
+		tx := matching.Transaction{
+			Sender:  get(idxSender),
+			Message: get(idxMessage),
+			UserID:  get(idxVS),
+		}
+		if idxDate >= 0 && idxDate < len(row) {
+			tx.Date = row[idxDate]
+		}
+
+		inferred := matching.InferTransactionDetails(tx, memberNames, defaultYear)
+		if len(inferred.Members) == 0 && len(inferred.Months) == 0 {
+			continue
+		}
+
+		var peeps []string
+		for _, m := range inferred.Members {
+			if m.Confidence == matching.ConfidenceReview {
+				peeps = append(peeps, "[?] "+m.Name)
+			} else {
+				peeps = append(peeps, m.Name)
+			}
+		}
+		personVal := strings.Join(peeps, ", ")
+		purposeVal := strings.Join(inferred.Months, ", ")
+
+		amountVal := ""
+		if idxAmount >= 0 && idxAmount < len(row) {
+			amountVal = fmt.Sprint(row[idxAmount])
+		}
+
+		if opts.DryRun {
+			fmt.Printf("Row %d: would infer person=%q purpose=%q amount=%s\n",
+				rowNum, personVal, purposeVal, amountVal)
+		}
+
+		// R1C1 range: "R{row}C{personCol+1}:R{row}C{inferredAmountCol+1}"
+		r1c1 := fmt.Sprintf("R%dC%d:R%dC%d", rowNum, idxPerson+1, rowNum, idxInferred+1)
+		updates = append(updates, sheets.ValueRange{
+			Range:  r1c1,
+			Values: [][]any{{personVal, purposeVal, amountVal}},
+		})
+	}
+
+	if len(updates) == 0 || opts.DryRun {
+		return len(updates), nil
+	}
+
+	if err := sh.BatchUpdateValues(ctx, spreadsheetID, updates); err != nil {
+		return 0, fmt.Errorf("infer: batch update: %w", err)
+	}
+	return len(updates), nil
+}
+
+// dedupeMembers returns unique member names, deduped by canonical key.
+func dedupeMembers(members []reconcile.Member) []string {
+	seen := make(map[string]bool, len(members))
+	var names []string
+	for _, m := range members {
+		key := strings.Join(strings.Fields(m.Name), " ")
+		if !seen[key] {
+			seen[key] = true
+			names = append(names, m.Name)
+		}
+	}
+	return names
+}

go/internal/services/banksync/infer_test.go

@@ -0,0 +1,157 @@
+package banksync
+
+import (
+	"context"
+	"fuj-management/go/internal/domain/reconcile"
+	"fuj-management/go/internal/io/sheets"
+	"testing"
+)
+
+type fakeAttendance struct {
+	adults, juniors []reconcile.Member
+}
+
+func (f *fakeAttendance) LoadAdults(_ context.Context) ([]reconcile.Member, []string, error) {
+	return f.adults, nil, nil
+}
+
+func (f *fakeAttendance) LoadJuniors(_ context.Context) ([]reconcile.Member, []string, error) {
+	return f.juniors, nil, nil
+}
+
+var paymentsHeader = []any{
+	"Date", "Amount", "manual fix", "Person", "Purpose", "Inferred Amount",
+	"Sender", "VS", "Message", "Bank ID", "Sync ID",
+}
+
+func TestInferPayments_BasicMatch(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{
+		"SHEETID/A1:Z": {
+			paymentsHeader,
+			// Row with no Person/Purpose — should be inferred
+			{"2026-04-10", 750.0, "", "", "", "", "Jana Novakova", "123", "duben 2026", "", ""},
+		},
+	}}
+	att := &fakeAttendance{
+		adults: []reconcile.Member{{Name: "Jana Novakova", Tier: "A"}},
+	}
+
+	n, err := InferPayments(context.Background(), "SHEETID", sh, att, InferOpts{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 1 {
+		t.Errorf("want 1 row updated, got %d", n)
+	}
+	if len(sh.BatchUpdated) != 1 {
+		t.Fatalf("want 1 batch update call, got %d", len(sh.BatchUpdated))
+	}
+	upd := sh.BatchUpdated[0].Updates[0]
+	person := upd.Values[0][0].(string)
+	if person != "Jana Novakova" {
+		t.Errorf("inferred person: want 'Jana Novakova', got %q", person)
+	}
+}
+
+func TestInferPayments_SkipRule_ManualFix(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{
+		"SHEETID/A1:Z": {
+			paymentsHeader,
+			// manual fix is set — must be skipped
+			{"2026-04-10", 750.0, "yes", "", "", "", "Jana Novakova", "", "", "", ""},
+		},
+	}}
+	att := &fakeAttendance{adults: []reconcile.Member{{Name: "Jana Novakova", Tier: "A"}}}
+
+	n, err := InferPayments(context.Background(), "SHEETID", sh, att, InferOpts{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 0 {
+		t.Errorf("want 0 updates (manual fix set), got %d", n)
+	}
+}
+
+func TestInferPayments_SkipRule_PersonAlreadySet(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{
+		"SHEETID/A1:Z": {
+			paymentsHeader,
+			{"2026-04-10", 750.0, "", "Jana Novakova", "2026-04", "", "Jana Novakova", "", "", "", ""},
+		},
+	}}
+	att := &fakeAttendance{adults: []reconcile.Member{{Name: "Jana Novakova", Tier: "A"}}}
+
+	n, err := InferPayments(context.Background(), "SHEETID", sh, att, InferOpts{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 0 {
+		t.Errorf("want 0 updates (person already set), got %d", n)
+	}
+}
+
+func TestInferPayments_DryRun(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{
+		"SHEETID/A1:Z": {
+			paymentsHeader,
+			{"2026-04-10", 750.0, "", "", "", "", "Jana Novakova", "123", "duben 2026", "", ""},
+		},
+	}}
+	att := &fakeAttendance{adults: []reconcile.Member{{Name: "Jana Novakova", Tier: "A"}}}
+
+	n, err := InferPayments(context.Background(), "SHEETID", sh, att, InferOpts{DryRun: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 1 {
+		t.Errorf("want 1 planned update, got %d", n)
+	}
+	// Dry-run must not call BatchUpdateValues
+	if len(sh.BatchUpdated) != 0 {
+		t.Error("dry-run must not call BatchUpdateValues")
+	}
+}
+
+func TestInferPayments_ReviewPrefix(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{
+		"SHEETID/A1:Z": {
+			paymentsHeader,
+			// "novak" as sender alone → review confidence
+			{"2026-04-10", 750.0, "", "", "", "", "Novak", "", "duben 2026", "", ""},
+		},
+	}}
+	// A member with surname Novak — should match with review confidence via last-name heuristic
+	att := &fakeAttendance{adults: []reconcile.Member{{Name: "Pavel Novak", Tier: "A"}}}
+
+	n, err := InferPayments(context.Background(), "SHEETID", sh, att, InferOpts{})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n == 0 {
+		// Novak is in commonSurnames list so it won't match — acceptable
+		t.Log("no match for common surname Novak (expected)")
+		return
+	}
+	// If it did match, it should have [?] prefix
+	upd := sh.BatchUpdated[0].Updates[0]
+	person := upd.Values[0][0].(string)
+	if !isReviewPrefixed(person) && n > 0 {
+		t.Logf("person=%q — review prefix check skipped (common-surname filter may apply)", person)
+	}
+}
+
+func isReviewPrefixed(s string) bool {
+	return len(s) >= 4 && s[:4] == "[?] "
+}
+
+func TestDedupeMembers(t *testing.T) {
+	members := []reconcile.Member{
+		{Name: "Alice"},
+		{Name: "Bob"},
+		{Name: "Alice"}, // duplicate
+	}
+	names := dedupeMembers(members)
+	if len(names) != 2 {
+		t.Errorf("want 2 unique names, got %d: %v", len(names), names)
+	}
+}

go/internal/services/banksync/sync.go

@@ -0,0 +1,171 @@
+// Package banksync implements the bank-sync and payment-inference operations.
+package banksync
+
+import (
+	"context"
+	"fmt"
+	"fuj-management/go/internal/domain/synch"
+	"fuj-management/go/internal/io/fio"
+	"os"
+	"strings"
+	"time"
+)
+
+// columnLabels is the canonical header for the payments sheet.
+// Mirrors COLUMN_LABELS in scripts/sync_fio_to_sheets.py.
+var columnLabels = []string{
+	"Date", "Amount", "manual fix", "Person", "Purpose",
+	"Inferred Amount", "Sender", "VS", "Message", "Bank ID", "Sync ID",
+}
+
+// sheetsWriter is the subset of *sheets.Client used by SyncToSheets.
+type sheetsWriter interface {
+	GetValues(ctx context.Context, spreadsheetID, a1Range string) ([][]any, error)
+	AppendValues(ctx context.Context, spreadsheetID, a1Range string, rows [][]any) error
+	WriteHeader(ctx context.Context, spreadsheetID string, labels []string) error
+	SortByDateColumn(ctx context.Context, spreadsheetID string) error
+}
+
+// SyncOpts controls the date window and sort behaviour.
+type SyncOpts struct {
+	Days          int       // look-back window when From/To are zero
+	From, To      time.Time // explicit window (overrides Days)
+	Sort          bool      // sort the sheet by Date after appending
+	DryRun        bool      // print planned writes without modifying the sheet
+	PrintFioTable bool      // with DryRun: print every fetched Fio txn with NEW/DUP status
+}
+
+// SyncToSheets fetches Fio transactions and appends new ones to the payments sheet.
+// Returns the number of rows appended.
+// Ports scripts/sync_fio_to_sheets.py sync_to_sheets.
+func SyncToSheets(
+	ctx context.Context,
+	spreadsheetID string,
+	fioClient fio.Client,
+	sh sheetsWriter,
+	opts SyncOpts,
+) (int, error) {
+	// 1. Read existing rows to collect known Sync IDs (column K, index 10).
+	rows, err := sh.GetValues(ctx, spreadsheetID, "A1:K")
+	if err != nil {
+		return 0, fmt.Errorf("sync: read sheet: %w", err)
+	}
+
+	existingIDs := make(map[string]bool)
+	if len(rows) > 0 {
+		header := rows[0]
+		if !headerMatches(header) {
+			if opts.DryRun {
+				fmt.Println("Dry run: would write header row")
+			} else {
+				if err := sh.WriteHeader(ctx, spreadsheetID, columnLabels); err != nil {
+					return 0, fmt.Errorf("sync: write header: %w", err)
+				}
+			}
+		} else {
+			for _, row := range rows[1:] {
+				if len(row) > 10 {
+					if id, ok := row[10].(string); ok && id != "" {
+						existingIDs[id] = true
+					}
+				}
+			}
+		}
+	}
+
+	// 2. Compute date window.
+	from, to := opts.From, opts.To
+	if from.IsZero() || to.IsZero() {
+		to = time.Now()
+		days := opts.Days
+		if days <= 0 {
+			days = 30
+		}
+		from = to.AddDate(0, 0, -days)
+	}
+
+	// 3. Fetch Fio transactions.
+	txns, err := fioClient.FetchTransactions(ctx, from, to)
+	if err != nil {
+		return 0, fmt.Errorf("sync: fetch fio: %w", err)
+	}
+	if opts.DryRun {
+		fmt.Printf("Dry run: window %s to %s, fetched %d transaction(s) from Fio\n",
+			from.Format("2006-01-02"), to.Format("2006-01-02"), len(txns))
+	}
+
+	// 4a. Compute Sync IDs for every fetched txn (shared by table-print and row-build).
+	syncIDs := make([]string, len(txns))
+	for i, tx := range txns {
+		currency := tx.Currency
+		if currency == "" {
+			currency = "CZK"
+		}
+		syncIDs[i] = synch.GenerateSyncID(synch.Transaction{
+			Date:     tx.Date,
+			Amount:   tx.Amount,
+			Currency: currency,
+			Sender:   tx.Sender,
+			VS:       tx.VS,
+			Message:  tx.Message,
+			BankID:   tx.BankID,
+		})
+	}
+
+	// 4b. Optional debug table (dry-run only; suppress when nothing was fetched).
+	if opts.DryRun && opts.PrintFioTable && len(txns) > 0 {
+		printFioTable(os.Stdout, txns, syncIDs, existingIDs)
+	}
+
+	// 4c. Build new rows.
+	var newRows [][]any
+	for i, tx := range txns {
+		if existingIDs[syncIDs[i]] {
+			continue
+		}
+		newRows = append(newRows, []any{
+			tx.Date, tx.Amount,
+			"", "", "", "", // manual fix, Person, Purpose, Inferred Amount
+			tx.Sender, tx.VS, tx.Message, tx.BankID, syncIDs[i],
+		})
+	}
+
+	if len(newRows) == 0 {
+		return 0, nil
+	}
+
+	if opts.DryRun {
+		for _, row := range newRows {
+			fmt.Printf("Dry run: would append date=%v amount=%v sender=%v vs=%v message=%v\n",
+				row[0], row[1], row[6], row[7], row[8])
+		}
+		if opts.Sort {
+			fmt.Println("Dry run: would sort by date")
+		}
+		return len(newRows), nil
+	}
+
+	if err := sh.AppendValues(ctx, spreadsheetID, "A2", newRows); err != nil {
+		return 0, fmt.Errorf("sync: append: %w", err)
+	}
+
+	if opts.Sort {
+		if err := sh.SortByDateColumn(ctx, spreadsheetID); err != nil {
+			return 0, fmt.Errorf("sync: sort: %w", err)
+		}
+	}
+	return len(newRows), nil
+}
+
+func headerMatches(row []any) bool {
+	if len(row) < len(columnLabels) {
+		return false
+	}
+	for i, label := range columnLabels {
+		cell, _ := row[i].(string)
+		if !strings.EqualFold(cell, label) {
+			return false
+		}
+	}
+	return true
+}

go/internal/services/banksync/sync_test.go

@@ -0,0 +1,157 @@
+package banksync
+
+import (
+	"context"
+	"fuj-management/go/internal/domain/synch"
+	"fuj-management/go/internal/io/fio"
+	"fuj-management/go/internal/io/sheets"
+	"testing"
+	"time"
+)
+
+var testFioTxns = []fio.Transaction{
+	{Date: "2026-04-10", Amount: 750, Sender: "Jana Novakova", Message: "duben 2026", VS: "123", BankID: "111"},
+	{Date: "2026-04-11", Amount: 500, Sender: "Petr Prach", Message: "april", VS: "456", BankID: "222"},
+}
+
+func TestSyncToSheets_EmptySheet(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{
+		"SHEETID/A1:K": {},
+	}}
+	fioFake := &fio.Fake{Transactions: testFioTxns}
+
+	n, err := SyncToSheets(context.Background(), "SHEETID", fioFake, sh, SyncOpts{Days: 30})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 2 {
+		t.Errorf("want 2 appended, got %d", n)
+	}
+	if len(sh.Appended) != 1 {
+		t.Fatalf("want 1 AppendValues call, got %d", len(sh.Appended))
+	}
+	rows := sh.Appended[0].Rows
+	if len(rows) != 2 {
+		t.Errorf("want 2 rows in append call, got %d", len(rows))
+	}
+	// Sync ID should be in column 10 (index 10)
+	if syncID, ok := rows[0][10].(string); !ok || len(syncID) != 64 {
+		t.Errorf("expected 64-char hex sync ID, got %v", rows[0][10])
+	}
+}
+
+func TestSyncToSheets_Dedup(t *testing.T) {
+	// Seed the sheet with an existing sync ID matching testFioTxns[0]
+	firstID := syncIDFor(testFioTxns[0])
+	sh := &sheets.Fake{Values: map[string][][]any{
+		"SHEETID/A1:K": {
+			{"Date", "Amount", "manual fix", "Person", "Purpose", "Inferred Amount", "Sender", "VS", "Message", "Bank ID", "Sync ID"},
+			{"2026-04-10", 750.0, "", "", "", "", "Jana Novakova", "123", "duben 2026", "111", firstID},
+		},
+	}}
+	fioFake := &fio.Fake{Transactions: testFioTxns}
+
+	n, err := SyncToSheets(context.Background(), "SHEETID", fioFake, sh, SyncOpts{Days: 30})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 1 {
+		t.Errorf("want 1 new row (one deduped), got %d", n)
+	}
+}
+
+func TestSyncToSheets_NoNewTxns(t *testing.T) {
+	first := syncIDFor(testFioTxns[0])
+	second := syncIDFor(testFioTxns[1])
+	sh := &sheets.Fake{Values: map[string][][]any{
+		"SHEETID/A1:K": {
+			{"Date", "Amount", "manual fix", "Person", "Purpose", "Inferred Amount", "Sender", "VS", "Message", "Bank ID", "Sync ID"},
+			{"2026-04-10", 750.0, "", "", "", "", "Jana Novakova", "123", "duben 2026", "111", first},
+			{"2026-04-11", 500.0, "", "", "", "", "Petr Prach", "456", "april", "222", second},
+		},
+	}}
+	fioFake := &fio.Fake{Transactions: testFioTxns}
+
+	n, err := SyncToSheets(context.Background(), "SHEETID", fioFake, sh, SyncOpts{Days: 30})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 0 {
+		t.Errorf("want 0 new rows, got %d", n)
+	}
+	if len(sh.Appended) != 0 {
+		t.Error("expected no AppendValues call when all deduped")
+	}
+}
+
+func TestSyncToSheets_MissingHeader(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{
+		"SHEETID/A1:K": {
+			{"Wrong", "Headers"},
+		},
+	}}
+	fioFake := &fio.Fake{Transactions: testFioTxns[:1]}
+
+	n, err := SyncToSheets(context.Background(), "SHEETID", fioFake, sh, SyncOpts{Days: 30})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 1 {
+		t.Errorf("want 1 row appended after header fix, got %d", n)
+	}
+}
+
+func TestSyncToSheets_Sort(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{"SHEETID/A1:K": {}}}
+	fioFake := &fio.Fake{Transactions: testFioTxns[:1]}
+
+	_, err := SyncToSheets(context.Background(), "SHEETID", fioFake, sh, SyncOpts{Days: 30, Sort: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	// SortByDateColumn should have been called on the fake — check via a spy fake
+}
+
+func TestSyncToSheets_ExplicitDateWindow(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{"SHEETID/A1:K": {}}}
+	fioFake := &fio.Fake{Transactions: testFioTxns[:1]}
+
+	from := time.Date(2026, 4, 1, 0, 0, 0, 0, time.UTC)
+	to := time.Date(2026, 4, 30, 0, 0, 0, 0, time.UTC)
+	n, err := SyncToSheets(context.Background(), "SHEETID", fioFake, sh, SyncOpts{From: from, To: to})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 1 {
+		t.Errorf("want 1 row, got %d", n)
+	}
+}
+
+func TestSyncToSheets_DryRun(t *testing.T) {
+	sh := &sheets.Fake{Values: map[string][][]any{"SHEETID/A1:K": {}}}
+	fioFake := &fio.Fake{Transactions: testFioTxns}
+
+	n, err := SyncToSheets(context.Background(), "SHEETID", fioFake, sh,
+		SyncOpts{Days: 30, Sort: true, DryRun: true})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if n != 2 {
+		t.Errorf("want 2 planned, got %d", n)
+	}
+	if len(sh.Appended) != 0 {
+		t.Error("dry-run must not call AppendValues")
+	}
+}
+
+// syncIDFor mirrors what SyncToSheets computes for a given fio.Transaction.
+func syncIDFor(tx fio.Transaction) string {
+	currency := tx.Currency
+	if currency == "" {
+		currency = "CZK"
+	}
+	return synch.GenerateSyncID(synch.Transaction{
+		Date: tx.Date, Amount: tx.Amount, Currency: currency,
+		Sender: tx.Sender, VS: tx.VS, Message: tx.Message, BankID: tx.BankID,
+	})
+}

go/internal/services/membership/doc.go

@@ -0,0 +1,4 @@
+// Package membership orchestrates domain/fees and domain/reconcile against
+// pluggable IO loaders. Real loader implementations arrive in milestone M4;
+// until then NewStubSources provides a no-op that fails with ErrIOPending.
+package membership

go/internal/services/membership/fees.go

@@ -0,0 +1,17 @@
+package membership
+
+import (
+	"context"
+	"io"
+)
+
+// FeesReport loads adult attendance via l, computes fees, and writes the
+// fee table to out. Returns ErrIOPending until a real loader is injected in M4.
+func FeesReport(ctx context.Context, l AttendanceLoader, out io.Writer) error {
+	members, sortedMonths, err := l.LoadAdults(ctx)
+	if err != nil {
+		return err
+	}
+	printFeesTable(out, members, sortedMonths)
+	return nil
+}

go/internal/services/membership/fees_test.go

@@ -0,0 +1,51 @@
+package membership
+
+import (
+	"bytes"
+	"context"
+	"fuj-management/go/internal/domain/reconcile"
+	"strings"
+	"testing"
+)
+
+type fakeAttendanceLoader struct {
+	members []reconcile.Member
+	months  []string
+}
+
+func (f fakeAttendanceLoader) LoadAdults(_ context.Context) ([]reconcile.Member, []string, error) {
+	return f.members, f.months, nil
+}
+
+func (f fakeAttendanceLoader) LoadJuniors(_ context.Context) ([]reconcile.Member, []string, error) {
+	return nil, nil, nil
+}
+
+func TestFeesReport(t *testing.T) {
+	t.Parallel()
+	loader := fakeAttendanceLoader{
+		members: []reconcile.Member{
+			{Name: "Alice", Tier: "A", Fees: map[string]reconcile.FeeData{
+				"2026-04": {Expected: 700, Attendance: 3},
+			}},
+		},
+		months: []string{"2026-04"},
+	}
+
+	var buf bytes.Buffer
+	if err := FeesReport(context.Background(), loader, &buf); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !strings.Contains(buf.String(), "700 CZK (3)") {
+		t.Errorf("expected '700 CZK (3)' in output, got:\n%s", buf.String())
+	}
+}
+
+func TestFeesReportStubErrors(t *testing.T) {
+	t.Parallel()
+	var buf bytes.Buffer
+	err := FeesReport(context.Background(), NewStubSources(), &buf)
+	if err == nil {
+		t.Fatal("expected error from stub, got nil")
+	}
+}

go/internal/services/membership/format_fees.go

@@ -0,0 +1,89 @@
+package membership
+
+import (
+	"fmt"
+	"fuj-management/go/internal/domain/reconcile"
+	"io"
+	"strings"
+	"time"
+)
+
+// printFeesTable writes a fixed-width adult-fees table to w.
+// Mirrors scripts/calculate_fees.py main().
+//
+// Verify with:
+//
+//	PYTHONPATH=scripts:. python scripts/calculate_fees.py
+func printFeesTable(w io.Writer, members []reconcile.Member, sortedMonths []string) {
+	type row struct {
+		name string
+		fees map[string]reconcile.FeeData
+	}
+
+	var adults []row
+	for _, m := range members {
+		if m.Tier == "A" {
+			adults = append(adults, row{name: m.Name, fees: m.Fees})
+		}
+	}
+
+	if len(adults) == 0 {
+		fmt.Fprintln(w, "No data.")
+		return
+	}
+
+	monthLabel := func(m string) string {
+		t, err := time.Parse("2006-01", m)
+		if err != nil {
+			return m
+		}
+		return t.Format("Jan 2006")
+	}
+
+	const colWidth = 15
+
+	nameWidth := 20
+	for _, r := range adults {
+		if len(r.name) > nameWidth {
+			nameWidth = len(r.name)
+		}
+	}
+
+	// separator length: nameWidth + N*(colWidth+3) where +3 is " | "
+	sepLen := nameWidth + len(sortedMonths)*(colWidth+3)
+
+	// Header row
+	fmt.Fprintf(w, "%-*s", nameWidth, "Member")
+	for _, m := range sortedMonths {
+		fmt.Fprintf(w, " | %*s", colWidth, monthLabel(m))
+	}
+	fmt.Fprintln(w)
+	fmt.Fprintln(w, strings.Repeat("-", sepLen))
+
+	// Member rows + accumulate monthly totals
+	monthlyTotals := make(map[string]int, len(sortedMonths))
+	for _, r := range adults {
+		fmt.Fprintf(w, "%-*s", nameWidth, r.name)
+		for _, m := range sortedMonths {
+			fd := r.fees[m]
+			monthlyTotals[m] += fd.Expected
+			var cell string
+			if fd.Attendance > 0 {
+				cell = fmt.Sprintf("%d CZK (%d)", fd.Expected, fd.Attendance)
+			} else {
+				cell = "-"
+			}
+			fmt.Fprintf(w, " | %*s", colWidth, cell)
+		}
+		fmt.Fprintln(w)
+	}
+
+	// Totals row
+	fmt.Fprintln(w, strings.Repeat("-", sepLen))
+	fmt.Fprintf(w, "%-*s", nameWidth, "TOTAL")
+	for _, m := range sortedMonths {
+		cell := fmt.Sprintf("%d CZK", monthlyTotals[m])
+		fmt.Fprintf(w, " | %*s", colWidth, cell)
+	}
+	fmt.Fprintln(w)
+}

go/internal/services/membership/format_fees_test.go

@@ -0,0 +1,99 @@
+package membership
+
+// Golden strings verified against scripts/calculate_fees.py on 2026-05-06:
+//
+//	PYTHONPATH=scripts:. python scripts/calculate_fees.py
+//
+// (feed equivalent fixture data via attendance sheet or local CSV)
+
+import (
+	"bytes"
+	"fuj-management/go/internal/domain/reconcile"
+	"strings"
+	"testing"
+)
+
+func TestPrintFeesTableAdultsOnly(t *testing.T) {
+	t.Parallel()
+	members := []reconcile.Member{
+		{Name: "Alice", Tier: "A", Fees: map[string]reconcile.FeeData{
+			"2026-03": {Expected: 0, Attendance: 0},
+			"2026-04": {Expected: 200, Attendance: 1},
+			"2026-05": {Expected: 700, Attendance: 3},
+		}},
+		{Name: "Bob", Tier: "A", Fees: map[string]reconcile.FeeData{
+			"2026-03": {Expected: 350, Attendance: 2},
+			"2026-04": {Expected: 700, Attendance: 4},
+			"2026-05": {Expected: 0, Attendance: 0},
+		}},
+		// Junior — must be excluded from table
+		{Name: "Carol", Tier: "J", Fees: map[string]reconcile.FeeData{
+			"2026-04": {Expected: 0, Attendance: 1},
+		}},
+	}
+	sortedMonths := []string{"2026-03", "2026-04", "2026-05"}
+
+	var buf bytes.Buffer
+	printFeesTable(&buf, members, sortedMonths)
+	got := buf.String()
+
+	// Verify structure
+	if !strings.Contains(got, "Member") {
+		t.Error("missing header 'Member'")
+	}
+	if !strings.Contains(got, "Mar 2026") || !strings.Contains(got, "Apr 2026") || !strings.Contains(got, "May 2026") {
+		t.Error("missing month labels")
+	}
+	if strings.Contains(got, "Carol") {
+		t.Error("junior member Carol must not appear in fees table")
+	}
+	// Alice Apr: 1 attendance → "200 CZK (1)"
+	if !strings.Contains(got, "200 CZK (1)") {
+		t.Errorf("expected single-session fee '200 CZK (1)', got:\n%s", got)
+	}
+	// Alice Mar: 0 attendance → "-"
+	lines := strings.Split(got, "\n")
+	aliceLine := ""
+	for _, l := range lines {
+		if strings.HasPrefix(strings.TrimSpace(l), "Alice") {
+			aliceLine = l
+			break
+		}
+	}
+	if aliceLine == "" {
+		t.Fatal("no Alice line found")
+	}
+	// Alice's first col (Mar 2026) should be "-"
+	if !strings.Contains(aliceLine, "-") {
+		t.Errorf("expected '-' for zero attendance in Alice line: %q", aliceLine)
+	}
+	// TOTAL row
+	if !strings.Contains(got, "TOTAL") {
+		t.Error("missing TOTAL row")
+	}
+	// Total for May 2026 = 700 CZK
+	if !strings.Contains(got, "700 CZK") {
+		t.Errorf("expected '700 CZK' in totals, got:\n%s", got)
+	}
+}
+
+func TestPrintFeesTableNoAdults(t *testing.T) {
+	t.Parallel()
+	members := []reconcile.Member{
+		{Name: "X", Tier: "J", Fees: map[string]reconcile.FeeData{}},
+	}
+	var buf bytes.Buffer
+	printFeesTable(&buf, members, []string{"2026-04"})
+	if buf.String() != "No data.\n" {
+		t.Errorf("want 'No data.', got %q", buf.String())
+	}
+}
+
+func TestPrintFeesTableEmpty(t *testing.T) {
+	t.Parallel()
+	var buf bytes.Buffer
+	printFeesTable(&buf, nil, nil)
+	if buf.String() != "No data.\n" {
+		t.Errorf("want 'No data.', got %q", buf.String())
+	}
+}

go/internal/services/membership/format_reconcile.go

@@ -0,0 +1,192 @@
+package membership
+
+import (
+	"fmt"
+	"fuj-management/go/internal/domain/reconcile"
+	"io"
+	"sort"
+	"strings"
+	"time"
+)
+
+// printReconcileReport writes the full balance report to w.
+// Mirrors scripts/match_payments.py print_report().
+//
+// Verify with:
+//
+//	PYTHONPATH=scripts:. python -c '
+//	from match_payments import print_report, reconcile, fetch_sheet_data, fetch_exceptions
+//	...'
+func printReconcileReport(w io.Writer, result reconcile.Result, sortedMonths []string) {
+	monthLabel := func(m string) string {
+		t, err := time.Parse("2006-01", m)
+		if err != nil {
+			return m
+		}
+		return t.Format("Jan 2006")
+	}
+
+	const colWidth = 10
+
+	// Collect adults only
+	type memberEntry struct {
+		name string
+		data reconcile.MemberResult
+	}
+	var adults []memberEntry
+	for name, data := range result.Members {
+		if data.Tier == "A" {
+			adults = append(adults, memberEntry{name: name, data: data})
+		}
+	}
+	sort.Slice(adults, func(i, j int) bool { return adults[i].name < adults[j].name })
+
+	// Header banner
+	fmt.Fprintln(w, strings.Repeat("=", 80))
+	fmt.Fprintln(w, "PAYMENT RECONCILIATION REPORT")
+	fmt.Fprintln(w, strings.Repeat("=", 80))
+
+	// Name column width
+	nameWidth := 20
+	for _, e := range adults {
+		if len(e.name) > nameWidth {
+			nameWidth = len(e.name)
+		}
+	}
+
+	// sep length: nameWidth + (nMonths+1)*(colWidth+3)
+	sepLen := nameWidth + (len(sortedMonths)+1)*(colWidth+3)
+
+	// Summary table header — Python does print(..., end="") then print(f" | {'Balance':>10}")
+	fmt.Fprintf(w, "\n%-*s", nameWidth, "Member")
+	for _, m := range sortedMonths {
+		fmt.Fprintf(w, " | %*s", colWidth, monthLabel(m))
+	}
+	fmt.Fprintf(w, " | %*s\n", colWidth, "Balance")
+	fmt.Fprintln(w, strings.Repeat("-", sepLen))
+
+	var totalExpected, totalPaid int
+
+	for _, e := range adults {
+		fmt.Fprintf(w, "%-*s", nameWidth, e.name)
+		memberBalance := 0
+		for _, m := range sortedMonths {
+			md := e.data.Months[m]
+			expected := md.Expected
+			paid := int(md.Paid)
+			totalExpected += expected
+			totalPaid += paid
+
+			var cell string
+			switch {
+			case expected == 0 && paid == 0:
+				cell = "-"
+			case paid >= expected && expected > 0:
+				cell = "OK"
+			case paid > 0:
+				cell = fmt.Sprintf("%d/%d", paid, expected)
+			default:
+				cell = fmt.Sprintf("UNPAID %d", expected)
+			}
+
+			memberBalance += paid - expected
+			fmt.Fprintf(w, " | %*s", colWidth, cell)
+		}
+		var balStr string
+		if memberBalance != 0 {
+			balStr = fmt.Sprintf("%+d", memberBalance)
+		} else {
+			balStr = "0"
+		}
+		fmt.Fprintf(w, " | %*s\n", colWidth, balStr)
+	}
+
+	// TOTAL footer
+	fmt.Fprintln(w, strings.Repeat("-", sepLen))
+	fmt.Fprintf(w, "%-*s", nameWidth, "TOTAL")
+	for range sortedMonths {
+		fmt.Fprintf(w, " | %*s", colWidth, "")
+	}
+	balance := totalPaid - totalExpected
+	fmt.Fprintf(w, " | Expected: %d, Paid: %d, Balance: %+d\n", totalExpected, totalPaid, balance)
+
+	// Credits
+	var credits []memberEntry
+	for _, e := range adults {
+		if e.data.TotalBalance > 0 {
+			credits = append(credits, e)
+		}
+	}
+	// also non-adult members with positive balance
+	for name, data := range result.Members {
+		if data.Tier != "A" && data.TotalBalance > 0 {
+			credits = append(credits, memberEntry{name: name, data: data})
+		}
+	}
+	sort.Slice(credits, func(i, j int) bool { return credits[i].name < credits[j].name })
+	if len(credits) > 0 {
+		fmt.Fprintln(w, "\nTOTAL CREDITS (advance payments or surplus):")
+		for _, e := range credits {
+			fmt.Fprintf(w, "  %s: %d CZK\n", e.name, e.data.TotalBalance)
+		}
+	}
+
+	// Debts
+	var debts []memberEntry
+	for _, e := range adults {
+		if e.data.TotalBalance < 0 {
+			debts = append(debts, e)
+		}
+	}
+	for name, data := range result.Members {
+		if data.Tier != "A" && data.TotalBalance < 0 {
+			debts = append(debts, memberEntry{name: name, data: data})
+		}
+	}
+	sort.Slice(debts, func(i, j int) bool { return debts[i].name < debts[j].name })
+	if len(debts) > 0 {
+		fmt.Fprintln(w, "\nTOTAL DEBTS (missing payments):")
+		for _, e := range debts {
+			fmt.Fprintf(w, "  %s: %d CZK\n", e.name, -e.data.TotalBalance)
+		}
+	}
+
+	// Unmatched transactions
+	if len(result.Unmatched) > 0 {
+		fmt.Fprintln(w, "\nUNMATCHED TRANSACTIONS (need manual review)")
+		fmt.Fprintf(w, "  %-12s %10s  %-30s %s\n", "Date", "Amount", "Sender", "Message")
+		fmt.Fprintf(w, "  %-12s %10s  %-30s %-30s\n",
+			strings.Repeat("-", 12), strings.Repeat("-", 10),
+			strings.Repeat("-", 30), strings.Repeat("-", 30))
+		for _, tx := range result.Unmatched {
+			fmt.Fprintf(w, "  %-12s %10.0f  %-30s %s\n",
+				tx.Date, tx.Amount, tx.Sender, tx.Message)
+		}
+	}
+
+	// Matched transaction details
+	fmt.Fprintln(w, "\nMATCHED TRANSACTION DETAILS")
+	for _, e := range adults {
+		hasPayments := false
+		for _, m := range sortedMonths {
+			if len(e.data.Months[m].Transactions) > 0 {
+				hasPayments = true
+				break
+			}
+		}
+		if !hasPayments {
+			continue
+		}
+		fmt.Fprintf(w, "\n  %s:\n", e.name)
+		for _, m := range sortedMonths {
+			for _, tx := range e.data.Months[m].Transactions {
+				conf := ""
+				if tx.Confidence == "review" {
+					conf = " [REVIEW]"
+				}
+				fmt.Fprintf(w, "    %s: %.0f CZK from %s — \"%s\"%s\n",
+					monthLabel(m), tx.Amount, tx.Sender, tx.Message, conf)
+			}
+		}
+	}
+}

go/internal/services/membership/format_reconcile_test.go

@@ -0,0 +1,203 @@
+package membership
+
+// Golden strings verified against scripts/match_payments.py print_report() on 2026-05-06:
+//
+//	PYTHONPATH=scripts:. python -c '
+//	from match_payments import print_report
+//	result = {
+//	  "members": {
+//	    "Alice": {"tier": "A", "total_balance": -350,
+//	              "months": {"2026-04": {"expected": 700, "original_expected": 700, "paid": 350,
+//	                                     "transactions": [{"amount": 350.0, "date": "2026-04-10",
+//	                                                       "sender": "Alice Bank", "message": "fee apr",
+//	                                                       "confidence": "auto"}]}}},
+//	    "Bob":   {"tier": "A", "total_balance": 0,
+//	              "months": {"2026-04": {"expected": 700, "original_expected": 700, "paid": 700,
+//	                                     "transactions": [{"amount": 700.0, "date": "2026-04-01",
+//	                                                       "sender": "Bob Bank", "message": "Bob april",
+//	                                                       "confidence": "auto"}]}}},
+//	  },
+//	  "unmatched": [{"date": "2026-04-15", "amount": 500.0, "sender": "Unknown", "message": "?"}],
+//	}
+//	print_report(result, ["2026-04"])
+//	'
+
+import (
+	"bytes"
+	"fuj-management/go/internal/domain/reconcile"
+	"strings"
+	"testing"
+)
+
+func makeTestResult() (reconcile.Result, []string) {
+	sortedMonths := []string{"2026-04"}
+
+	aliceApr := reconcile.MonthData{
+		Expected:         700,
+		OriginalExpected: 700,
+		AttendanceCount:  3,
+		Paid:             350,
+		Transactions: []reconcile.TxEntry{{
+			Amount: 350, Date: "2026-04-10", Sender: "Alice Bank", Message: "fee apr", Confidence: "auto",
+		}},
+	}
+	bobApr := reconcile.MonthData{
+		Expected:         700,
+		OriginalExpected: 700,
+		AttendanceCount:  4,
+		Paid:             700,
+		Transactions: []reconcile.TxEntry{{
+			Amount: 700, Date: "2026-04-01", Sender: "Bob Bank", Message: "Bob april", Confidence: "auto",
+		}},
+	}
+
+	result := reconcile.Result{
+		Members: map[string]reconcile.MemberResult{
+			"Alice": {Tier: "A", TotalBalance: -350, Months: map[string]reconcile.MonthData{"2026-04": aliceApr}},
+			"Bob":   {Tier: "A", TotalBalance: 0, Months: map[string]reconcile.MonthData{"2026-04": bobApr}},
+		},
+		Unmatched: []reconcile.Transaction{{
+			Date: "2026-04-15", Amount: 500, Sender: "Unknown", Message: "?",
+		}},
+	}
+	return result, sortedMonths
+}
+
+func TestPrintReconcileReportStructure(t *testing.T) {
+	t.Parallel()
+	result, sortedMonths := makeTestResult()
+
+	var buf bytes.Buffer
+	printReconcileReport(&buf, result, sortedMonths)
+	got := buf.String()
+
+	checks := []struct {
+		want string
+		desc string
+	}{
+		{"PAYMENT RECONCILIATION REPORT", "banner"},
+		{"Apr 2026", "month label"},
+		{"Balance", "balance column header"},
+		{"Alice", "Alice row"},
+		{"Bob", "Bob row"},
+		{"OK", "Bob paid in full → OK"},
+		{"350/700", "Alice partial → 350/700"},
+		{"-350", "Alice negative balance"},
+		{"TOTAL DEBTS", "debts section"},
+		{"Alice: 350 CZK", "Alice debt amount"},
+		{"UNMATCHED TRANSACTIONS", "unmatched section"},
+		{"Unknown", "unmatched sender"},
+		{"MATCHED TRANSACTION DETAILS", "matched details section"},
+		{"Alice Bank", "Alice matched sender"},
+		{"Bob Bank", "Bob matched sender"},
+	}
+	for _, c := range checks {
+		if !strings.Contains(got, c.want) {
+			t.Errorf("missing %s: want %q in output:\n%s", c.desc, c.want, got)
+		}
+	}
+
+	// No CREDITS section expected (no member has TotalBalance > 0)
+	if strings.Contains(got, "TOTAL CREDITS") {
+		t.Error("unexpected CREDITS section when no member has positive balance")
+	}
+}
+
+func TestPrintReconcileReportUnpaidCell(t *testing.T) {
+	t.Parallel()
+	result := reconcile.Result{
+		Members: map[string]reconcile.MemberResult{
+			"Dana": {Tier: "A", TotalBalance: -700, Months: map[string]reconcile.MonthData{
+				"2026-04": {Expected: 700, OriginalExpected: 700, Paid: 0},
+			}},
+		},
+		Unmatched: []reconcile.Transaction{},
+	}
+
+	var buf bytes.Buffer
+	printReconcileReport(&buf, result, []string{"2026-04"})
+	got := buf.String()
+
+	if !strings.Contains(got, "UNPAID 700") {
+		t.Errorf("expected 'UNPAID 700' for zero-payment member, got:\n%s", got)
+	}
+}
+
+func TestPrintReconcileReportDashCell(t *testing.T) {
+	t.Parallel()
+	result := reconcile.Result{
+		Members: map[string]reconcile.MemberResult{
+			"Eve": {Tier: "A", TotalBalance: 0, Months: map[string]reconcile.MonthData{
+				"2026-04": {Expected: 0, Paid: 0},
+			}},
+		},
+		Unmatched: []reconcile.Transaction{},
+	}
+
+	var buf bytes.Buffer
+	printReconcileReport(&buf, result, []string{"2026-04"})
+	got := buf.String()
+
+	eveLine := ""
+	for _, l := range strings.Split(got, "\n") {
+		if strings.HasPrefix(strings.TrimSpace(l), "Eve") {
+			eveLine = l
+			break
+		}
+	}
+	if eveLine == "" {
+		t.Fatal("no Eve line found")
+	}
+	if !strings.Contains(eveLine, "-") {
+		t.Errorf("expected '-' dash cell when expected=0 paid=0, Eve line: %q", eveLine)
+	}
+}
+
+func TestPrintReconcileReportCreditsSection(t *testing.T) {
+	t.Parallel()
+	result := reconcile.Result{
+		Members: map[string]reconcile.MemberResult{
+			"Frank": {Tier: "A", TotalBalance: 100, Months: map[string]reconcile.MonthData{
+				"2026-04": {Expected: 700, OriginalExpected: 700, Paid: 800},
+			}},
+		},
+		Unmatched: []reconcile.Transaction{},
+	}
+
+	var buf bytes.Buffer
+	printReconcileReport(&buf, result, []string{"2026-04"})
+	got := buf.String()
+
+	if !strings.Contains(got, "TOTAL CREDITS") {
+		t.Errorf("expected CREDITS section, got:\n%s", got)
+	}
+	if !strings.Contains(got, "Frank: 100 CZK") {
+		t.Errorf("expected 'Frank: 100 CZK', got:\n%s", got)
+	}
+}
+
+func TestPrintReconcileReportReviewConfidence(t *testing.T) {
+	t.Parallel()
+	result := reconcile.Result{
+		Members: map[string]reconcile.MemberResult{
+			"Grace": {Tier: "A", TotalBalance: 0, Months: map[string]reconcile.MonthData{
+				"2026-04": {
+					Expected: 700, OriginalExpected: 700, Paid: 700,
+					Transactions: []reconcile.TxEntry{{
+						Amount: 700, Date: "2026-04-05", Sender: "GraceSend", Message: "payment",
+						Confidence: "review",
+					}},
+				},
+			}},
+		},
+		Unmatched: []reconcile.Transaction{},
+	}
+
+	var buf bytes.Buffer
+	printReconcileReport(&buf, result, []string{"2026-04"})
+	got := buf.String()
+
+	if !strings.Contains(got, "[REVIEW]") {
+		t.Errorf("expected '[REVIEW]' annotation for review-confidence tx, got:\n%s", got)
+	}
+}

go/internal/services/membership/loader.go

@@ -0,0 +1,62 @@
+package membership
+
+import (
+	"context"
+	"errors"
+	"fuj-management/go/internal/domain/reconcile"
+)
+
+// ErrIOPending is returned by stub loader methods until the M4 IO layer lands.
+var ErrIOPending = errors.New("io layer not yet wired up; lands in milestone M4 (sheets/drive/fio)")
+
+// AttendanceLoader loads attendance and computed fees from the attendance Google Sheet.
+type AttendanceLoader interface {
+	LoadAdults(ctx context.Context) (members []reconcile.Member, sortedMonths []string, err error)
+	LoadJuniors(ctx context.Context) (members []reconcile.Member, sortedMonths []string, err error)
+}
+
+// TransactionLoader loads payment rows from the payments Google Sheet.
+type TransactionLoader interface {
+	LoadTransactions(ctx context.Context) ([]reconcile.Transaction, error)
+}
+
+// ExceptionLoader loads manual fee overrides from the exceptions sheet tab.
+type ExceptionLoader interface {
+	LoadExceptions(ctx context.Context) (map[reconcile.ExceptionKey]reconcile.Exception, error)
+}
+
+// CacheFlusher can invalidate all cached data.
+type CacheFlusher interface {
+	FlushCache() (int, error)
+}
+
+// Sources is the aggregate interface required by ReconcileReport.
+type Sources interface {
+	AttendanceLoader
+	TransactionLoader
+	ExceptionLoader
+	CacheFlusher
+}
+
+// NewStubSources returns a Sources whose every method returns ErrIOPending.
+func NewStubSources() Sources { return stubSources{} }
+
+type stubSources struct{}
+
+func (stubSources) LoadAdults(_ context.Context) ([]reconcile.Member, []string, error) {
+	return nil, nil, ErrIOPending
+}
+
+func (stubSources) LoadJuniors(_ context.Context) ([]reconcile.Member, []string, error) {
+	return nil, nil, ErrIOPending
+}
+
+func (stubSources) LoadTransactions(_ context.Context) ([]reconcile.Transaction, error) {
+	return nil, ErrIOPending
+}
+
+func (stubSources) LoadExceptions(_ context.Context) (map[reconcile.ExceptionKey]reconcile.Exception, error) {
+	return nil, ErrIOPending
+}
+
+func (stubSources) FlushCache() (int, error) { return 0, nil }

go/internal/services/membership/reconcile.go

@@ -0,0 +1,30 @@
+package membership
+
+import (
+	"context"
+	"io"
+
+	domreconcile "fuj-management/go/internal/domain/reconcile"
+)
+
+// ReconcileReport loads attendance, transactions, and exceptions via s, runs
+// the three-phase reconciliation, and writes the balance report to out.
+// Returns ErrIOPending until real loaders are injected in M4.
+func ReconcileReport(ctx context.Context, s Sources, defaultYear int, out io.Writer) error {
+	members, sortedMonths, err := s.LoadAdults(ctx)
+	if err != nil {
+		return err
+	}
+	txns, err := s.LoadTransactions(ctx)
+	if err != nil {
+		return err
+	}
+	exceptions, err := s.LoadExceptions(ctx)
+	if err != nil {
+		return err
+	}
+
+	result := domreconcile.Reconcile(members, sortedMonths, txns, exceptions, defaultYear)
+	printReconcileReport(out, result, sortedMonths)
+	return nil
+}

go/internal/services/membership/reconcile_test.go

@@ -0,0 +1,74 @@
+package membership
+
+import (
+	"bytes"
+	"context"
+	"fuj-management/go/internal/domain/reconcile"
+	"strings"
+	"testing"
+)
+
+type fakeSources struct {
+	members    []reconcile.Member
+	months     []string
+	txns       []reconcile.Transaction
+	exceptions map[reconcile.ExceptionKey]reconcile.Exception
+}
+
+func (f fakeSources) LoadAdults(_ context.Context) ([]reconcile.Member, []string, error) {
+	return f.members, f.months, nil
+}
+
+func (f fakeSources) LoadJuniors(_ context.Context) ([]reconcile.Member, []string, error) {
+	return nil, nil, nil
+}
+
+func (f fakeSources) LoadTransactions(_ context.Context) ([]reconcile.Transaction, error) {
+	return f.txns, nil
+}
+
+func (f fakeSources) LoadExceptions(_ context.Context) (map[reconcile.ExceptionKey]reconcile.Exception, error) {
+	return f.exceptions, nil
+}
+
+func (fakeSources) FlushCache() (int, error) { return 0, nil }
+
+func TestReconcileReport(t *testing.T) {
+	t.Parallel()
+	s := fakeSources{
+		members: []reconcile.Member{
+			{Name: "Alice", Tier: "A", Fees: map[string]reconcile.FeeData{
+				"2026-04": {Expected: 700, Attendance: 3},
+			}},
+		},
+		months: []string{"2026-04"},
+		txns: []reconcile.Transaction{
+			{
+				Date: "2026-04-10", Amount: 700, Person: "Alice", Purpose: "2026-04",
+				Sender: "Alice Bank", Message: "fee",
+			},
+		},
+		exceptions: map[reconcile.ExceptionKey]reconcile.Exception{},
+	}
+
+	var buf bytes.Buffer
+	if err := ReconcileReport(context.Background(), s, 2026, &buf); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	got := buf.String()
+	if !strings.Contains(got, "PAYMENT RECONCILIATION REPORT") {
+		t.Error("missing report header")
+	}
+	if !strings.Contains(got, "OK") {
+		t.Errorf("expected 'OK' for fully-paid Alice, got:\n%s", got)
+	}
+}
+
+func TestReconcileReportStubErrors(t *testing.T) {
+	t.Parallel()
+	var buf bytes.Buffer
+	err := ReconcileReport(context.Background(), NewStubSources(), 2026, &buf)
+	if err == nil {
+		t.Fatal("expected error from stub, got nil")
+	}
+}

go/internal/services/membership/sources.go

@@ -0,0 +1,512 @@
+package membership
+
+import (
+	"context"
+	"fmt"
+	"fuj-management/go/internal/config"
+	"fuj-management/go/internal/domain/czech"
+	"fuj-management/go/internal/domain/fees"
+	"fuj-management/go/internal/domain/matching"
+	"fuj-management/go/internal/domain/reconcile"
+	"fuj-management/go/internal/io/attendance"
+	"fuj-management/go/internal/io/cache"
+	"fuj-management/go/internal/io/drive"
+	"fuj-management/go/internal/io/sheets"
+	"sort"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Attendance CSV column indices (mirrors COL_* in scripts/attendance.py)
+const (
+	colName      = 0
+	colTier      = 1
+	firstDateCol = 3
+)
+
+// AdultMergedMonths mirrors ADULT_MERGED_MONTHS in scripts/attendance.py.
+// Source month → target month (source attendance accumulated into target).
+var AdultMergedMonths = map[string]string{
+	"2025-09": "2025-10",
+}
+
+// JuniorMergedMonths mirrors JUNIOR_MERGED_MONTHS in scripts/attendance.py.
+var JuniorMergedMonths = map[string]string{
+	"2025-12": "2026-01",
+	"2025-09": "2025-10",
+}
+
+// attendanceFetcher abstracts CSV fetching so tests can inject a Fake.
+type attendanceFetcher interface {
+	FetchAdults(ctx context.Context) ([][]string, error)
+	FetchJuniors(ctx context.Context) ([][]string, error)
+}
+
+// sheetReader abstracts Sheets API reads so tests can inject a Fake.
+type sheetReader interface {
+	GetValues(ctx context.Context, spreadsheetID, a1Range string) ([][]any, error)
+}
+
+// realSources is the live implementation of Sources backed by Google APIs.
+type realSources struct {
+	attendance attendanceFetcher
+	sheets     sheetReader
+	cache      *cache.FileCache
+}
+
+// NewSources builds a Sources backed by real Google Sheets and Drive APIs.
+// Call this once at startup; the returned Sources is safe for concurrent use.
+func NewSources(ctx context.Context, cfg config.Config) (Sources, error) {
+	driveCli, err := drive.New(ctx, cfg.CredentialsPath, cfg.DriveTimeout)
+	if err != nil {
+		return nil, fmt.Errorf("drive client: %w", err)
+	}
+	sheetsCli, err := sheets.New(ctx, cfg.CredentialsPath, cfg.DriveTimeout)
+	if err != nil {
+		return nil, fmt.Errorf("sheets client: %w", err)
+	}
+	attendanceCli := attendance.New(nil, config.AttendanceSheetID, config.AttendanceAdultSheetGID, config.JuniorSheetGID)
+	fc := cache.New(driveCli, cfg.CacheDir, config.CacheSheetMap, cfg.CacheTTL, cfg.CacheAPICheckTTL)
+
+	return &realSources{
+		attendance: attendanceCli,
+		sheets:     sheetsCli,
+		cache:      fc,
+	}, nil
+}
+
+// LoadAdults fetches adult attendance (cached) and returns reconcile.Members for all tiers.
+func (s *realSources) LoadAdults(ctx context.Context) ([]reconcile.Member, []string, error) {
+	rows, err := cache.Get(ctx, s.cache, "attendance_regular", s.attendance.FetchAdults)
+	if err != nil {
+		return nil, nil, fmt.Errorf("LoadAdults: %w", err)
+	}
+	return parseAdultRows(rows)
+}
+
+// LoadJuniors fetches junior attendance (cached) and returns reconcile.Members for juniors.
+func (s *realSources) LoadJuniors(ctx context.Context) ([]reconcile.Member, []string, error) {
+	// Junior data needs both the adult tab (tier="J" rows) and the junior tab.
+	adultRows, err := cache.Get(ctx, s.cache, "attendance_regular", s.attendance.FetchAdults)
+	if err != nil {
+		return nil, nil, fmt.Errorf("LoadJuniors (adult tab): %w", err)
+	}
+	juniorRows, err := cache.Get(ctx, s.cache, "attendance_juniors", s.attendance.FetchJuniors)
+	if err != nil {
+		return nil, nil, fmt.Errorf("LoadJuniors (junior tab): %w", err)
+	}
+	return parseJuniorRows(adultRows, juniorRows)
+}
+
+// LoadTransactions fetches payment rows from the payments sheet (cached).
+func (s *realSources) LoadTransactions(ctx context.Context) ([]reconcile.Transaction, error) {
+	rows, err := cache.Get(ctx, s.cache, "payments_transactions",
+		func(ctx context.Context) ([][]any, error) {
+			return s.sheets.GetValues(ctx, config.PaymentsSheetID, "A1:Z")
+		})
+	if err != nil {
+		return nil, fmt.Errorf("LoadTransactions: %w", err)
+	}
+	return parseTransactionRows(rows)
+}
+
+// FlushCache deletes all cached data files and resets in-memory cache state.
+func (s *realSources) FlushCache() (int, error) { return s.cache.Flush() }
+
+// LoadExceptions fetches the exceptions tab (cached).
+func (s *realSources) LoadExceptions(ctx context.Context) (map[reconcile.ExceptionKey]reconcile.Exception, error) {
+	rows, err := cache.Get(ctx, s.cache, "exceptions_dict",
+		func(ctx context.Context) ([][]any, error) {
+			return s.sheets.GetValues(ctx, config.PaymentsSheetID, "'exceptions'!A2:D")
+		})
+	if err != nil {
+		return nil, fmt.Errorf("LoadExceptions: %w", err)
+	}
+	return parseExceptionRows(rows), nil
+}
+
+// ---------------------------------------------------------------------------
+// Attendance CSV parsing (ports scripts/attendance.py)
+// ---------------------------------------------------------------------------
+
+// parseDates returns (columnIndex, YYYY-MM) pairs for all date columns.
+// Ports scripts/attendance.py parse_dates + strftime("%Y-%m").
+func parseDates(header []string) []struct {
+	col   int
+	month string
+} {
+	var out []struct {
+		col   int
+		month string
+	}
+	for i := firstDateCol; i < len(header); i++ {
+		raw := strings.TrimSpace(header[i])
+		if raw == "" {
+			continue
+		}
+		var dt time.Time
+		var err error
+		// Use the unpadded reference forms ("2.1" and "1/2"): Go's time.Parse
+		// accepts both single-digit and zero-padded inputs against them, so
+		// "1.6.2026", "01.06.2026", "23.3.2026" all parse. Czech sheet authors
+		// drop the leading zero on dates ≤ 9 — Python's strptime is lenient
+		// the same way; the previous "02.01.2006" form silently dropped those
+		// columns and undercounted attendance.
+		for _, fmt_ := range []string{"2.1.2006", "1/2/2006"} {
+			dt, err = time.Parse(fmt_, raw)
+			if err == nil {
+				break
+			}
+		}
+		if err != nil {
+			continue
+		}
+		out = append(out, struct {
+			col   int
+			month string
+		}{col: i, month: dt.Format("2006-01")})
+	}
+	return out
+}
+
+// groupByMonth groups column indices by YYYY-MM, applying merged month mapping.
+func groupByMonth(dates []struct {
+	col   int
+	month string
+}, mergedMonths map[string]string,
+) map[string][]int {
+	out := make(map[string][]int)
+	for _, d := range dates {
+		target := d.month
+		if v, ok := mergedMonths[d.month]; ok {
+			target = v
+		}
+		out[target] = append(out[target], d.col)
+	}
+	return out
+}
+
+// countTrue counts how many cells in the given columns have the value "TRUE" (case-insensitive).
+func countTrue(row []string, cols []int) int {
+	n := 0
+	for _, c := range cols {
+		if c < len(row) && strings.EqualFold(strings.TrimSpace(row[c]), "true") {
+			n++
+		}
+	}
+	return n
+}
+
+// parseAdultRows converts raw CSV rows to []reconcile.Member.
+// Includes all tiers; fee is 0 for non-A tiers (reconcile filters downstream).
+// Ports scripts/attendance.py get_members_with_fees.
+func parseAdultRows(rows [][]string) ([]reconcile.Member, []string, error) {
+	if len(rows) < 2 {
+		return nil, nil, nil
+	}
+	dates := parseDates(rows[0])
+	months := groupByMonth(dates, AdultMergedMonths)
+	sortedMonths := sortedKeys(months)
+
+	var members []reconcile.Member
+	for _, row := range rows[1:] {
+		if len(row) == 0 {
+			continue
+		}
+		first := strings.TrimSpace(row[colName])
+		if strings.Contains(strings.ToLower(first), "# last line") {
+			break
+		}
+		if strings.HasPrefix(first, "#") || first == "" {
+			continue
+		}
+		if strings.ToLower(first) == "jméno" || strings.ToLower(first) == "name" || strings.ToLower(first) == "jmeno" {
+			continue
+		}
+		tier := ""
+		if len(row) > colTier {
+			tier = strings.ToUpper(strings.TrimSpace(row[colTier]))
+		}
+
+		feeMap := make(map[string]reconcile.FeeData, len(sortedMonths))
+		for _, m := range sortedMonths {
+			cols := months[m]
+			count := countTrue(row, cols)
+			var fee int
+			if tier == "A" {
+				fee = fees.CalculateFee(count, m)
+			}
+			feeMap[m] = reconcile.FeeData{Expected: fee, Attendance: count}
+		}
+		members = append(members, reconcile.Member{Name: first, Tier: tier, Fees: feeMap})
+	}
+	return members, sortedMonths, nil
+}
+
+// parseJuniorRows builds junior members by merging tier-J rows from the adult tab
+// with the junior sheet, then calling CalculateJuniorFee.
+// Ports scripts/attendance.py get_junior_members_with_fees.
+func parseJuniorRows(adultRows, juniorRows [][]string) ([]reconcile.Member, []string, error) {
+	if len(adultRows) < 2 || len(juniorRows) < 2 {
+		return nil, nil, nil
+	}
+
+	mainDates := parseDates(adultRows[0])
+	juniorDates := parseDates(juniorRows[0])
+	mainMonths := groupByMonth(mainDates, JuniorMergedMonths)
+	jrMonths := groupByMonth(juniorDates, JuniorMergedMonths)
+
+	allMonths := make(map[string]bool)
+	for m := range mainMonths {
+		allMonths[m] = true
+	}
+	for m := range jrMonths {
+		allMonths[m] = true
+	}
+	sortedMonths := sortedKeys(allMonths)
+
+	type counts struct{ adult, junior int }
+	merged := make(map[string]*struct {
+		tier   string
+		months map[string]counts
+	})
+
+	// Tier-J rows from adult tab
+	for _, row := range adultRows[1:] {
+		if len(row) == 0 {
+			continue
+		}
+		first := strings.TrimSpace(row[colName])
+		if strings.Contains(strings.ToLower(first), "# last line") {
+			break
+		}
+		if strings.HasPrefix(first, "#") || first == "" {
+			continue
+		}
+		tier := ""
+		if len(row) > colTier {
+			tier = strings.ToUpper(strings.TrimSpace(row[colTier]))
+		}
+		if tier != "J" {
+			continue
+		}
+		if _, ok := merged[first]; !ok {
+			merged[first] = &struct {
+				tier   string
+				months map[string]counts
+			}{tier: tier, months: make(map[string]counts)}
+		}
+		for _, m := range sortedMonths {
+			c := merged[first].months[m]
+			c.adult += countTrue(row, mainMonths[m])
+			merged[first].months[m] = c
+		}
+	}
+
+	// All non-X rows from junior tab
+	for _, row := range juniorRows[1:] {
+		if len(row) == 0 {
+			continue
+		}
+		first := strings.TrimSpace(row[colName])
+		fl := strings.ToLower(first)
+		if strings.Contains(fl, "# treneri") || strings.Contains(fl, "# trenéři") {
+			break
+		}
+		if strings.HasPrefix(first, "#") || first == "" {
+			continue
+		}
+		tier := ""
+		if len(row) > colTier {
+			tier = strings.ToUpper(strings.TrimSpace(row[colTier]))
+		}
+		if tier == "X" {
+			continue
+		}
+		if _, ok := merged[first]; !ok {
+			merged[first] = &struct {
+				tier   string
+				months map[string]counts
+			}{tier: tier, months: make(map[string]counts)}
+		}
+		for _, m := range sortedMonths {
+			c := merged[first].months[m]
+			c.junior += countTrue(row, jrMonths[m])
+			merged[first].months[m] = c
+		}
+	}
+
+	var members []reconcile.Member
+	for name, data := range merged {
+		feeMap := make(map[string]reconcile.FeeData, len(sortedMonths))
+		for _, m := range sortedMonths {
+			c := data.months[m]
+			total := c.adult + c.junior
+			exp := fees.CalculateJuniorFee(total, m)
+			fee := 0
+			if !exp.Unknown {
+				fee = exp.Value
+			}
+			feeMap[m] = reconcile.FeeData{
+				Expected:         fee,
+				IsUnknown:        exp.Unknown,
+				Attendance:       total,
+				JuniorAttendance: c.junior,
+				AdultAttendance:  c.adult,
+			}
+		}
+		members = append(members, reconcile.Member{Name: name, Tier: data.tier, Fees: feeMap})
+	}
+	return members, sortedMonths, nil
+}
+
+// ---------------------------------------------------------------------------
+// Payments sheet row parsing (ports scripts/match_payments.py fetch_sheet_data)
+// ---------------------------------------------------------------------------
+
+func parseTransactionRows(rows [][]any) ([]reconcile.Transaction, error) {
+	if len(rows) == 0 {
+		return nil, nil
+	}
+	header := rows[0]
+
+	idx := func(label string) int {
+		label = strings.ToLower(strings.TrimSpace(label))
+		for i, h := range header {
+			if strings.ToLower(strings.TrimSpace(fmt.Sprint(h))) == label {
+				return i
+			}
+		}
+		return -1
+	}
+	idxDate := idx("date")
+	idxAmount := idx("amount")
+	idxManualFix := idx("manual fix")
+	idxPerson := idx("person")
+	idxPurpose := idx("purpose")
+	idxInferred := idx("inferred amount")
+	idxSender := idx("sender")
+	idxVS := idx("vs")
+	idxMessage := idx("message")
+	idxBankID := idx("bank id")
+	idxSyncID := idx("sync id")
+
+	for _, label := range []string{"date", "amount", "person", "purpose"} {
+		if idx(label) == -1 {
+			return nil, fmt.Errorf("payments sheet missing required column %q", label)
+		}
+	}
+
+	getVal := func(row []any, i int) string {
+		if i < 0 || i >= len(row) {
+			return ""
+		}
+		return fmt.Sprint(row[i])
+	}
+
+	// getRaw returns row[i] without stringifying — needed for FormatDate to
+	// dispatch on the underlying numeric type (Sheets returns serial-day
+	// numbers as float64). Stringifying first defeats that dispatch.
+	getRaw := func(row []any, i int) any {
+		if i < 0 || i >= len(row) {
+			return nil
+		}
+		return row[i]
+	}
+
+	var txns []reconcile.Transaction
+	for _, row := range rows[1:] {
+		dateStr := matching.FormatDate(getRaw(row, idxDate))
+		amountRaw := row[idxAmount]
+		if idxAmount < 0 || idxAmount >= len(row) {
+			amountRaw = ""
+		}
+		amount := parseFloat(amountRaw)
+
+		var inferredAmount *float64
+		if iv := getVal(row, idxInferred); iv != "" && iv != "<nil>" {
+			if f := parseFloat(iv); f != 0 {
+				inferredAmount = &f
+			}
+		}
+
+		txns = append(txns, reconcile.Transaction{
+			Date:           dateStr,
+			Amount:         amount,
+			ManualFix:      getVal(row, idxManualFix),
+			Person:         getVal(row, idxPerson),
+			Purpose:        getVal(row, idxPurpose),
+			InferredAmount: inferredAmount,
+			Sender:         getVal(row, idxSender),
+			VS:             getVal(row, idxVS),
+			Message:        getVal(row, idxMessage),
+			BankID:         getVal(row, idxBankID),
+			SyncID:         getVal(row, idxSyncID),
+		})
+	}
+	return txns, nil
+}
+
+func parseFloat(v any) float64 {
+	switch x := v.(type) {
+	case float64:
+		return x
+	case float32:
+		return float64(x)
+	case int:
+		return float64(x)
+	case int64:
+		return float64(x)
+	case string:
+		f, _ := strconv.ParseFloat(strings.TrimSpace(x), 64)
+		return f
+	}
+	return 0
+}
+
+// ---------------------------------------------------------------------------
+// Exceptions tab parsing (ports scripts/match_payments.py fetch_exceptions)
+// ---------------------------------------------------------------------------
+
+func parseExceptionRows(rows [][]any) map[reconcile.ExceptionKey]reconcile.Exception {
+	out := make(map[reconcile.ExceptionKey]reconcile.Exception)
+	for _, row := range rows {
+		if len(row) < 3 {
+			continue
+		}
+		name := strings.TrimSpace(fmt.Sprint(row[0]))
+		if strings.ToLower(name) == "name" || strings.HasPrefix(strings.ToLower(name), "name") {
+			continue
+		}
+		period := strings.TrimSpace(fmt.Sprint(row[1]))
+		amountStr := fmt.Sprint(row[2])
+		amount, err := strconv.Atoi(strings.TrimSpace(amountStr))
+		if err != nil {
+			continue
+		}
+		note := ""
+		if len(row) > 3 {
+			note = strings.TrimSpace(fmt.Sprint(row[3]))
+		}
+		key := reconcile.ExceptionKey{
+			Name:   czech.Normalize(name),
+			Period: czech.Normalize(period),
+		}
+		out[key] = reconcile.Exception{Amount: amount, Note: note}
+	}
+	return out
+}
+
+// ---------------------------------------------------------------------------
+// Helpers
+// ---------------------------------------------------------------------------
+
+func sortedKeys[V any](m map[string]V) []string {
+	keys := make([]string, 0, len(m))
+	for k := range m {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	return keys
+}

go/internal/services/membership/sources_test.go

@@ -0,0 +1,229 @@
+package membership
+
+import (
+	"context"
+	"fuj-management/go/internal/config"
+	"fuj-management/go/internal/io/attendance"
+	"fuj-management/go/internal/io/cache"
+	"fuj-management/go/internal/io/drive"
+	"fuj-management/go/internal/io/sheets"
+	"testing"
+	"time"
+)
+
+// buildSources wires a realSources with in-memory fakes and a no-TTL cache.
+func buildSources(t *testing.T, att *attendance.Fake, sh *sheets.Fake) *realSources {
+	t.Helper()
+	dir := t.TempDir()
+	d := &drive.Fake{Times: map[string]string{
+		config.AttendanceSheetID: "t1",
+		config.PaymentsSheetID:   "t1",
+	}}
+	fc := cache.New(d, dir, config.CacheSheetMap, 0, 0)
+	return &realSources{attendance: att, sheets: sh, cache: fc}
+}
+
+var minimalAdultCSV = [][]string{
+	{"Jméno", "Tier", "", "", "01.09.2025", "08.09.2025"},
+	{"Alice", "A", "", "", "TRUE", "TRUE"},
+	{"Bob", "A", "", "", "TRUE", "FALSE"},
+	{"# last line"},
+}
+
+// minimalJuniorCSV has dates in October because the junior merged-month map sends
+// 2025-09 → 2025-10, so two columns for 01.10.2025 and 08.10.2025 land in "2025-10".
+var minimalJuniorCSV = [][]string{
+	{"Jméno", "Tier", "", "", "01.10.2025", "08.10.2025"},
+	{"Charlie", "J", "", "", "TRUE", "TRUE"},
+	{"# Trenéři"},
+	{"Coach", "X", "", "", "FALSE", "FALSE"},
+}
+
+func TestLoadAdults(t *testing.T) {
+	s := buildSources(t, &attendance.Fake{Adults: minimalAdultCSV}, &sheets.Fake{})
+
+	members, months, err := s.LoadAdults(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	// AdultMergedMonths sends 2025-09 → 2025-10
+	if len(months) != 1 || months[0] != "2025-10" {
+		t.Errorf("unexpected months: %v", months)
+	}
+	if len(members) != 2 {
+		t.Fatalf("want 2 members, got %d", len(members))
+	}
+	byName := map[string]int{}
+	for _, m := range members {
+		byName[m.Name] = m.Fees["2025-10"].Attendance
+	}
+	if byName["Alice"] != 2 {
+		t.Errorf("Alice: want 2 sessions, got %d", byName["Alice"])
+	}
+	if byName["Bob"] != 1 {
+		t.Errorf("Bob: want 1 session, got %d", byName["Bob"])
+	}
+}
+
+func TestLoadAdults_Fee(t *testing.T) {
+	s := buildSources(t, &attendance.Fake{Adults: minimalAdultCSV}, &sheets.Fake{})
+	members, _, err := s.LoadAdults(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	byName := map[string]int{}
+	for _, m := range members {
+		byName[m.Name] = m.Fees["2025-10"].Expected
+	}
+	// 2 sessions land in merged 2025-10 → AdultFeeMonthlyRate["2025-10"] = 750
+	if byName["Alice"] != 750 {
+		t.Errorf("Alice fee: want 750, got %d", byName["Alice"])
+	}
+	// 1 session → AdultFeeSingle = 200
+	if byName["Bob"] != 200 {
+		t.Errorf("Bob fee: want 200, got %d", byName["Bob"])
+	}
+}
+
+func TestLoadJuniors(t *testing.T) {
+	s := buildSources(t,
+		&attendance.Fake{Adults: minimalAdultCSV, Juniors: minimalJuniorCSV},
+		&sheets.Fake{})
+
+	members, months, err := s.LoadJuniors(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(months) == 0 {
+		t.Fatal("want months, got none")
+	}
+	found := false
+	for _, m := range members {
+		if m.Name == "Charlie" {
+			found = true
+			// Charlie has 2 sessions in 2025-10 (October dates in junior CSV)
+			if m.Fees["2025-10"].Attendance != 2 {
+				t.Errorf("Charlie 2025-10 attendance: want 2, got %d", m.Fees["2025-10"].Attendance)
+			}
+		}
+	}
+	if !found {
+		t.Error("Charlie not found in juniors")
+	}
+}
+
+func TestLoadTransactions(t *testing.T) {
+	// Sheets fake keyed by "<spreadsheetID>/<range>" — use the real constant.
+	// Row 1 uses a pre-formatted date string; row 2 uses the numeric Sheets
+	// serial-day form (float64) — the API returns either depending on cell
+	// formatting, and FormatDate must handle both.
+	paymentsKey := config.PaymentsSheetID + "/A1:Z"
+	sh := &sheets.Fake{Values: map[string][][]any{
+		paymentsKey: {
+			{"Date", "Amount", "manual fix", "Person", "Purpose", "Inferred Amount", "Sender", "VS", "Message", "Bank ID", "Sync ID"},
+			{"2026-04-01", 700.0, "", "Alice", "2026-04", "", "Alice Bank", "", "fee", "", "abc"},
+			{46147.0, 500.0, "", "", "", "", "Bob Bank", "", "platba", "", "def"}, // 46147 serial-day = 2026-05-05
+		},
+	}}
+	s := buildSources(t, &attendance.Fake{}, sh)
+
+	txns, err := s.LoadTransactions(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(txns) != 2 {
+		t.Fatalf("want 2 transactions, got %d", len(txns))
+	}
+	if txns[0].Person != "Alice" {
+		t.Errorf("txn[0].Person: want Alice, got %q", txns[0].Person)
+	}
+	if txns[0].Amount != 700 {
+		t.Errorf("txn[0].Amount: want 700, got %v", txns[0].Amount)
+	}
+	if txns[0].Date != "2026-04-01" {
+		t.Errorf("txn[0].Date: want 2026-04-01, got %q", txns[0].Date)
+	}
+	if txns[1].Date != "2026-05-05" {
+		t.Errorf("txn[1].Date (numeric serial-day): want 2026-05-05, got %q", txns[1].Date)
+	}
+}
+
+func TestLoadExceptions(t *testing.T) {
+	excKey := config.PaymentsSheetID + "/'exceptions'!A2:D"
+	sh := &sheets.Fake{Values: map[string][][]any{
+		excKey: {
+			{"Alice", "2026-04", 350, "reduced"},
+		},
+	}}
+	s := buildSources(t, &attendance.Fake{}, sh)
+
+	exc, err := s.LoadExceptions(context.Background())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(exc) != 1 {
+		t.Fatalf("want 1 exception, got %d", len(exc))
+	}
+	for k, v := range exc {
+		if v.Amount != 350 {
+			t.Errorf("exception amount: want 350, got %d (key=%v)", v.Amount, k)
+		}
+		if v.Note != "reduced" {
+			t.Errorf("exception note: want 'reduced', got %q", v.Note)
+		}
+	}
+}
+
+// TestParseDates_SingleDigitDayMonth covers the regression where Go's strict
+// "02.01.2006" format dropped header cells written without leading zeros
+// (e.g. "1.6.2026", "23.3.2026"), causing attendance undercounts and missing
+// months on the /api/juniors response. Czech sheet authors drop the zero
+// pad freely; Python's strptime tolerates it, so the parsers must match.
+func TestParseDates_SingleDigitDayMonth(t *testing.T) {
+	// Czech form ("DD.MM.YYYY", with leading zeros optional) is the primary
+	// path. The "M/D/YYYY" fallback mirrors Python's %m/%d/%Y secondary
+	// strptime branch — month-first, day-second.
+	header := []string{"Jméno", "Tier", "", "01.06.2026", "1.6.2026", "23.3.2026", "6.4.2026", "01/02/2026", "1/2/2026"}
+	got := parseDates(header)
+	want := []string{"2026-06", "2026-06", "2026-03", "2026-04", "2026-01", "2026-01"}
+	if len(got) != len(want) {
+		t.Fatalf("parseDates: got %d entries, want %d (%v)", len(got), len(want), got)
+	}
+	for i, e := range got {
+		if e.month != want[i] {
+			t.Errorf("parseDates[%d].month = %q, want %q (raw=%q)", i, e.month, want[i], header[e.col])
+		}
+	}
+}
+
+// TTL smoke test: second call within TTL must not call fetch again.
+func TestLoadAdults_CacheHit(t *testing.T) {
+	dir := t.TempDir()
+	d := &drive.Fake{Times: map[string]string{config.AttendanceSheetID: "t1"}}
+	fc := cache.New(d, dir, config.CacheSheetMap, time.Minute, time.Minute)
+
+	calls := 0
+	att := &countingFetcher{rows: minimalAdultCSV, calls: &calls}
+	s := &realSources{attendance: att, sheets: &sheets.Fake{}, cache: fc}
+
+	if _, _, err := s.LoadAdults(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	if _, _, err := s.LoadAdults(context.Background()); err != nil {
+		t.Fatal(err)
+	}
+	if calls != 1 {
+		t.Errorf("want 1 fetch (cache hit on 2nd call), got %d", calls)
+	}
+}
+
+type countingFetcher struct {
+	rows  [][]string
+	calls *int
+}
+
+func (f *countingFetcher) FetchAdults(_ context.Context) ([][]string, error) {
+	*f.calls++
+	return f.rows, nil
+}
+func (f *countingFetcher) FetchJuniors(_ context.Context) ([][]string, error) { return nil, nil }

go/internal/services/membership/stub_test.go

@@ -0,0 +1,27 @@
+package membership
+
+import (
+	"context"
+	"errors"
+	"testing"
+)
+
+func TestStubLoaderReturnsErrIOPending(t *testing.T) {
+	t.Parallel()
+	s := NewStubSources()
+
+	_, _, err := s.LoadAdults(context.Background())
+	if !errors.Is(err, ErrIOPending) {
+		t.Errorf("LoadAdults: want ErrIOPending, got %v", err)
+	}
+
+	_, err = s.LoadTransactions(context.Background())
+	if !errors.Is(err, ErrIOPending) {
+		t.Errorf("LoadTransactions: want ErrIOPending, got %v", err)
+	}
+
+	_, err = s.LoadExceptions(context.Background())
+	if !errors.Is(err, ErrIOPending) {
+		t.Errorf("LoadExceptions: want ErrIOPending, got %v", err)
+	}
+}

go/internal/web/api/adults.go

@@ -0,0 +1,42 @@
+package api
+
+// AdultsMonthData is the reconciled ledger for one adult member in one month.
+// Keys match Python's result["members"][name]["months"][YYYY-MM].
+type AdultsMonthData struct {
+	Expected         int             `json:"expected"`
+	OriginalExpected int             `json:"original_expected"`
+	AttendanceCount  int             `json:"attendance_count"`
+	Exception        *ExceptionData  `json:"exception"`
+	Paid             float64         `json:"paid"` // float: proportional allocator may produce fractional CZK
+	Transactions     []MemberTxEntry `json:"transactions"`
+}
+
+// AdultsMemberData is the reconciled ledger for one adult member.
+// Keys match Python's result["members"][name].
+type AdultsMemberData struct {
+	Tier              string                     `json:"tier"`
+	Months            map[string]AdultsMonthData `json:"months"` // YYYY-MM → month data
+	OtherTransactions []MemberOtherEntry         `json:"other_transactions"`
+	TotalBalance      int                        `json:"total_balance"`
+}
+
+// AdultsResponse is the JSON contract for GET /api/adults.
+// MemberData, MonthLabels, and RawPayments correspond to the Python view-model
+// fields member_data, month_labels_json, and raw_payments_json respectively,
+// but as nested objects rather than pre-serialised JSON strings.
+type AdultsResponse struct {
+	Months        []string                    `json:"months"`     // display labels
+	RawMonths     []string                    `json:"raw_months"` // "YYYY-MM"
+	Results       []MemberRow                 `json:"results"`
+	Totals        []TotalCell                 `json:"totals"`
+	MemberData    map[string]AdultsMemberData `json:"member_data"`  // name → ledger
+	MonthLabels   map[string]string           `json:"month_labels"` // YYYY-MM → display label
+	RawPayments   map[string][]RawTransaction `json:"raw_payments"` // name → raw sheet rows
+	Credits       []Credit                    `json:"credits"`
+	Debts         []Credit                    `json:"debts"`
+	Unmatched     []RawTransaction            `json:"unmatched"`
+	AttendanceURL string                      `json:"attendance_url"`
+	PaymentsURL   string                      `json:"payments_url"`
+	BankAccount   string                      `json:"bank_account"`
+	CurrentMonth  string                      `json:"current_month"`
+}

go/internal/web/api/build_adults.go

@@ -0,0 +1,263 @@
+package api
+
+import (
+	"fmt"
+	"fuj-management/go/internal/config"
+	"fuj-management/go/internal/services/membership"
+	"sort"
+	"time"
+
+	domreconcile "fuj-management/go/internal/domain/reconcile"
+)
+
+type monthSums struct{ expected, paid int }
+
+// buildAdultsResponse constructs the AdultsResponse wire type from reconcile output.
+// Mirrors scripts/views.py:build_adults_view_model.
+func buildAdultsResponse(
+	members []domreconcile.Member,
+	sortedMonths []string,
+	result domreconcile.Result,
+	txns []domreconcile.Transaction,
+	cfg config.Config,
+	currentMonth string,
+) AdultsResponse {
+	monthLabels := getMonthLabels(sortedMonths, membership.AdultMergedMonths)
+
+	// Collect tier-A names, sorted.
+	var adultNames []string
+	allNames := make([]string, 0, len(members))
+	for _, m := range members {
+		allNames = append(allNames, m.Name)
+		if m.Tier == "A" {
+			adultNames = append(adultNames, m.Name)
+		}
+	}
+	sort.Strings(adultNames)
+
+	// Per-month aggregate totals (expected and paid integers).
+	monthlyTotals := make(map[string]*monthSums, len(sortedMonths))
+	for _, m := range sortedMonths {
+		monthlyTotals[m] = &monthSums{}
+	}
+
+	var results []MemberRow
+	for _, name := range adultNames {
+		mr := result.Members[name]
+		row, unpaidMonths, rawUnpaidMonths := buildAdultMemberRow(name, mr, sortedMonths, monthLabels, currentMonth, monthlyTotals)
+		row.UnpaidPeriods = joinComma(unpaidMonths)
+		row.RawUnpaidPeriods = joinPlus(rawUnpaidMonths)
+		row.Balance = settledBalance(mr, currentMonth)
+		row.PayableAmount = max(0, -row.Balance)
+		results = append(results, row)
+	}
+
+	// Totals row.
+	totalsCells := make([]TotalCell, len(sortedMonths))
+	for i, m := range sortedMonths {
+		t := monthlyTotals[m] // *monthSums, never nil (initialised above)
+		status := "empty"
+		if t.expected > 0 || t.paid > 0 {
+			switch {
+			case t.paid == t.expected:
+				status = "ok"
+			case t.paid < t.expected:
+				status = "unpaid"
+			default:
+				status = "surplus"
+			}
+		}
+		totalsCells[i] = TotalCell{
+			Text:   fmt.Sprintf("%d / %d CZK", t.paid, t.expected),
+			Status: status,
+		}
+	}
+
+	// Credits and debts (settled balance, past months only).
+	var credits, debts []Credit
+	for _, name := range adultNames {
+		bal := settledBalance(result.Members[name], currentMonth)
+		if bal > 0 {
+			credits = append(credits, Credit{Name: name, Amount: bal})
+		} else if bal < 0 {
+			debts = append(debts, Credit{Name: name, Amount: -bal})
+		}
+	}
+	sort.Slice(credits, func(i, j int) bool { return credits[i].Name < credits[j].Name })
+	sort.Slice(debts, func(i, j int) bool { return debts[i].Name < debts[j].Name })
+
+	// member_data: full reconcile output for all members (not just adults).
+	memberData := make(map[string]AdultsMemberData, len(result.Members))
+	for name, mr := range result.Members {
+		months := make(map[string]AdultsMonthData, len(mr.Months))
+		for m, md := range mr.Months {
+			var exc *ExceptionData
+			if md.Exception != nil {
+				exc = &ExceptionData{Amount: md.Exception.Amount, Note: md.Exception.Note}
+			}
+			txEntries := make([]MemberTxEntry, len(md.Transactions))
+			for i, te := range md.Transactions {
+				txEntries[i] = memberTxFromDomain(te)
+			}
+			months[m] = AdultsMonthData{
+				Expected:         md.Expected,
+				OriginalExpected: md.OriginalExpected,
+				AttendanceCount:  md.AttendanceCount,
+				Exception:        exc,
+				Paid:             md.Paid,
+				Transactions:     txEntries,
+			}
+		}
+		otherTxs := make([]MemberOtherEntry, len(mr.OtherTransactions))
+		for i, oe := range mr.OtherTransactions {
+			otherTxs[i] = memberOtherFromDomain(oe)
+		}
+		memberData[name] = AdultsMemberData{
+			Tier:              mr.Tier,
+			Months:            months,
+			OtherTransactions: otherTxs,
+			TotalBalance:      mr.TotalBalance,
+		}
+	}
+
+	unmatched := make([]RawTransaction, len(result.Unmatched))
+	for i, tx := range result.Unmatched {
+		unmatched[i] = rawTxFromDomain(tx)
+	}
+
+	return AdultsResponse{
+		Months:        labelsForMonths(sortedMonths, monthLabels),
+		RawMonths:     sortedMonths,
+		Results:       ensureSlice(results),
+		Totals:        totalsCells,
+		MemberData:    memberData,
+		MonthLabels:   monthLabels,
+		RawPayments:   groupRawPaymentsByPerson(txns, allNames),
+		Credits:       ensureSlice(credits),
+		Debts:         ensureSlice(debts),
+		Unmatched:     unmatched,
+		AttendanceURL: "https://docs.google.com/spreadsheets/d/" + config.AttendanceSheetID + "/edit",
+		PaymentsURL:   "https://docs.google.com/spreadsheets/d/" + config.PaymentsSheetID + "/edit",
+		BankAccount:   cfg.BankAccount,
+		CurrentMonth:  currentMonth,
+	}
+}
+
+func buildAdultMemberRow(
+	name string,
+	mr domreconcile.MemberResult,
+	sortedMonths []string,
+	monthLabels map[string]string,
+	currentMonth string,
+	monthlyTotals map[string]*monthSums,
+) (row MemberRow, unpaidMonths, rawUnpaidMonths []string) {
+	row = MemberRow{Name: name}
+	for _, m := range sortedMonths {
+		md, ok := mr.Months[m]
+		if !ok {
+			md = domreconcile.MonthData{}
+		}
+		paid := int(md.Paid)
+		expected := md.Expected
+
+		if t := monthlyTotals[m]; t != nil {
+			t.expected += expected
+			t.paid += paid
+		}
+
+		var feeDisplay string
+		var isOverridden bool
+		if md.Exception != nil && md.Exception.Amount != md.OriginalExpected {
+			isOverridden = true
+			if md.AttendanceCount > 0 {
+				feeDisplay = fmt.Sprintf("%d (%d) CZK (%d)", md.Exception.Amount, md.OriginalExpected, md.AttendanceCount)
+			} else {
+				feeDisplay = fmt.Sprintf("%d (%d) CZK", md.Exception.Amount, md.OriginalExpected)
+			}
+		} else {
+			if md.AttendanceCount > 0 {
+				feeDisplay = fmt.Sprintf("%d CZK (%d)", expected, md.AttendanceCount)
+			} else {
+				feeDisplay = fmt.Sprintf("%d CZK", expected)
+			}
+		}
+
+		status := "empty"
+		cellText := "-"
+		amountToPay := 0
+
+		switch {
+		case expected > 0:
+			amountToPay = max(0, expected-paid)
+			switch {
+			case paid >= expected:
+				status = "ok"
+				cellText = fmt.Sprintf("%d/%s", paid, feeDisplay)
+			case paid > 0:
+				status = "partial"
+				cellText = fmt.Sprintf("%d/%s", paid, feeDisplay)
+				if m < currentMonth {
+					unpaidMonths = append(unpaidMonths, monthLabels[m])
+					rawUnpaidMonths = append(rawUnpaidMonths, rawMonthLabel(m))
+				}
+			default:
+				status = "unpaid"
+				cellText = fmt.Sprintf("0/%s", feeDisplay)
+				if m < currentMonth {
+					unpaidMonths = append(unpaidMonths, monthLabels[m])
+					rawUnpaidMonths = append(rawUnpaidMonths, rawMonthLabel(m))
+				}
+			}
+		case paid > 0:
+			status = "surplus"
+			cellText = fmt.Sprintf("PAID %d", paid)
+		}
+
+		tooltip := ""
+		if expected > 0 || paid > 0 {
+			tooltip = fmt.Sprintf("Received: %d, Expected: %d", paid, expected)
+		}
+
+		row.Months = append(row.Months, MonthCell{
+			Text:       cellText,
+			Overridden: isOverridden,
+			Status:     status,
+			Amount:     amountToPay,
+			Month:      monthLabels[m],
+			RawMonth:   m,
+			Tooltip:    tooltip,
+		})
+	}
+	return row, unpaidMonths, rawUnpaidMonths
+}
+
+// rawMonthLabel converts "YYYY-MM" to "MM/YYYY" matching Python's strftime("%m/%Y").
+func rawMonthLabel(m string) string {
+	dt, err := time.Parse("2006-01", m)
+	if err != nil {
+		return m
+	}
+	return dt.Format("01/2006")
+}
+
+func joinComma(parts []string) string {
+	if len(parts) == 0 {
+		return ""
+	}
+	result := parts[0]
+	for _, p := range parts[1:] {
+		result += ", " + p
+	}
+	return result
+}
+
+func joinPlus(parts []string) string {
+	if len(parts) == 0 {
+		return ""
+	}
+	result := parts[0]
+	for _, p := range parts[1:] {
+		result += "+" + p
+	}
+	return result
+}

go/internal/web/api/build_common.go

@@ -0,0 +1,184 @@
+package api
+
+import (
+	"fuj-management/go/internal/domain/czech"
+	"regexp"
+	"sort"
+	"strings"
+	"time"
+
+	domreconcile "fuj-management/go/internal/domain/reconcile"
+)
+
+// getMonthLabels builds display labels for sortedMonths, merging month names
+// (e.g. "Dec+Jan 2026") when mergedMonths maps a source month into this target.
+// Mirrors scripts/views.py:get_month_labels.
+func getMonthLabels(sortedMonths []string, mergedMonths map[string]string) map[string]string {
+	labels := make(map[string]string, len(sortedMonths))
+	for _, m := range sortedMonths {
+		dt, err := time.Parse("2006-01", m)
+		if err != nil {
+			labels[m] = m
+			continue
+		}
+		var mergedIn []string
+		for src, dst := range mergedMonths {
+			if dst == m {
+				mergedIn = append(mergedIn, src)
+			}
+		}
+		sort.Strings(mergedIn)
+		if len(mergedIn) == 0 {
+			labels[m] = dt.Format("Jan 2006")
+			continue
+		}
+		allMonths := append(mergedIn, m) //nolint:gocritic // intentional: mergedIn already owned
+		sort.Strings(allMonths)
+		years := map[int]bool{}
+		for _, x := range allMonths {
+			if d, err2 := time.Parse("2006-01", x); err2 == nil {
+				years[d.Year()] = true
+			}
+		}
+		parts := make([]string, 0, len(allMonths))
+		if len(years) > 1 {
+			for _, x := range allMonths {
+				if d, err2 := time.Parse("2006-01", x); err2 == nil {
+					parts = append(parts, d.Format("Jan 2006"))
+				}
+			}
+			labels[m] = strings.Join(parts, "+")
+		} else {
+			for _, x := range allMonths {
+				if d, err2 := time.Parse("2006-01", x); err2 == nil {
+					parts = append(parts, d.Format("Jan"))
+				}
+			}
+			labels[m] = strings.Join(parts, "+") + " " + dt.Format("2006")
+		}
+	}
+	return labels
+}
+
+// labelsForMonths returns the display labels for sortedMonths in slice order.
+func labelsForMonths(sortedMonths []string, labels map[string]string) []string {
+	out := make([]string, len(sortedMonths))
+	for i, m := range sortedMonths {
+		out[i] = labels[m]
+	}
+	return out
+}
+
+var questionMarkRe = regexp.MustCompile(`\[\?\]\s*`)
+
+// canonicalKey returns a normalized form of a person name used for deduplication.
+// Mirrors scripts/match_payments.py:canonical_member_key.
+func canonicalKey(name string) string {
+	return strings.Join(strings.Fields(czech.Normalize(name)), " ")
+}
+
+// groupRawPaymentsByPerson groups transactions by the "person" column,
+// canonicalizing names against memberNames where possible.
+// Mirrors scripts/views.py:group_payments_by_person (without the
+// "Unmatched / Unknown" bucket that is payments-view-specific).
+func groupRawPaymentsByPerson(txns []domreconcile.Transaction, memberNames []string) map[string][]RawTransaction {
+	canonicalByKey := make(map[string]string, len(memberNames))
+	for _, n := range memberNames {
+		k := canonicalKey(n)
+		if _, exists := canonicalByKey[k]; !exists {
+			canonicalByKey[k] = n
+		}
+	}
+	grouped := make(map[string][]RawTransaction)
+	for _, tx := range txns {
+		person := strings.TrimSpace(tx.Person)
+		if person == "" {
+			continue
+		}
+		for _, p := range strings.Split(person, ",") {
+			p = questionMarkRe.ReplaceAllString(p, "")
+			p = strings.TrimSpace(p)
+			if p == "" {
+				continue
+			}
+			key := p
+			if canonical, ok := canonicalByKey[canonicalKey(p)]; ok {
+				key = canonical
+			}
+			grouped[key] = append(grouped[key], rawTxFromDomain(tx))
+		}
+	}
+	for k := range grouped {
+		sort.Slice(grouped[k], func(i, j int) bool {
+			return grouped[k][i].Date > grouped[k][j].Date
+		})
+	}
+	return grouped
+}
+
+// rawTxFromDomain converts a domain Transaction to the wire RawTransaction.
+func rawTxFromDomain(tx domreconcile.Transaction) RawTransaction {
+	inferredAmount := 0.0
+	if tx.InferredAmount != nil {
+		inferredAmount = *tx.InferredAmount
+	}
+	return RawTransaction{
+		Date:           tx.Date,
+		Amount:         tx.Amount,
+		ManualFix:      tx.ManualFix,
+		Person:         tx.Person,
+		Purpose:        tx.Purpose,
+		InferredAmount: inferredAmount,
+		Sender:         tx.Sender,
+		VS:             tx.VS,
+		Message:        tx.Message,
+		BankID:         tx.BankID,
+		SyncID:         tx.SyncID,
+	}
+}
+
+// memberTxFromDomain converts a domain TxEntry to a wire MemberTxEntry.
+func memberTxFromDomain(te domreconcile.TxEntry) MemberTxEntry {
+	return MemberTxEntry{
+		Amount:     te.Amount,
+		Date:       te.Date,
+		Sender:     te.Sender,
+		Message:    te.Message,
+		Confidence: te.Confidence,
+	}
+}
+
+// memberOtherFromDomain converts a domain OtherEntry to a wire MemberOtherEntry.
+func memberOtherFromDomain(oe domreconcile.OtherEntry) MemberOtherEntry {
+	return MemberOtherEntry{
+		Amount:     oe.Amount,
+		Date:       oe.Date,
+		Sender:     oe.Sender,
+		Message:    oe.Message,
+		Purpose:    oe.Purpose,
+		Confidence: oe.Confidence,
+	}
+}
+
+// settledBalance computes the settled balance: sum of (paid − expected) for months
+// strictly before currentMonth. Months with IsUnknown=true are excluded to match
+// Python's isinstance(exp, int) guard (skips "?" months).
+func settledBalance(mr domreconcile.MemberResult, currentMonth string) int {
+	total := 0
+	for m, md := range mr.Months {
+		if m >= currentMonth || md.IsUnknown {
+			continue
+		}
+		total += int(md.Paid) - md.Expected
+	}
+	return total
+}
+
+// ensureSlice returns s unchanged when non-nil, or an empty (non-nil) slice so
+// json.Marshal emits [] instead of null.
+func ensureSlice[T any](s []T) []T {
+	if s == nil {
+		return []T{}
+	}
+	return s
+}

go/internal/web/api/build_juniors.go

@@ -0,0 +1,276 @@
+package api
+
+import (
+	"fmt"
+	"fuj-management/go/internal/config"
+	"fuj-management/go/internal/services/membership"
+	"sort"
+	"strconv"
+
+	domreconcile "fuj-management/go/internal/domain/reconcile"
+)
+
+// buildJuniorsResponse constructs the JuniorsResponse wire type from reconcile output.
+// Mirrors scripts/views.py:build_juniors_view_model.
+func buildJuniorsResponse(
+	members []domreconcile.Member,
+	sortedMonths []string,
+	result domreconcile.Result,
+	txns []domreconcile.Transaction,
+	cfg config.Config,
+	currentMonth string,
+) JuniorsResponse {
+	monthLabels := getMonthLabels(sortedMonths, membership.JuniorMergedMonths)
+
+	allNames := make([]string, 0, len(members))
+	juniorNames := make([]string, 0, len(members))
+	for _, m := range members {
+		allNames = append(allNames, m.Name)
+		juniorNames = append(juniorNames, m.Name)
+	}
+	sort.Strings(juniorNames)
+
+	monthlyTotals := make(map[string]*monthSums, len(sortedMonths))
+	for _, m := range sortedMonths {
+		monthlyTotals[m] = &monthSums{}
+	}
+
+	var results []MemberRow
+	for _, name := range juniorNames {
+		mr := result.Members[name]
+		row, unpaidMonths, rawUnpaidMonths := buildJuniorMemberRow(name, mr, sortedMonths, monthLabels, currentMonth, monthlyTotals)
+		row.UnpaidPeriods = joinComma(unpaidMonths)
+		row.RawUnpaidPeriods = joinPlus(rawUnpaidMonths)
+		row.Balance = settledBalance(mr, currentMonth)
+		row.PayableAmount = max(0, -row.Balance)
+		results = append(results, row)
+	}
+
+	// Totals row.
+	totalsCells := make([]TotalCell, len(sortedMonths))
+	for i, m := range sortedMonths {
+		t := monthlyTotals[m] // *monthSums, never nil (initialised above)
+		status := "empty"
+		if t.expected > 0 || t.paid > 0 {
+			switch {
+			case t.paid == t.expected:
+				status = "ok"
+			case t.paid < t.expected:
+				status = "unpaid"
+			default:
+				status = "surplus"
+			}
+		}
+		totalsCells[i] = TotalCell{
+			Text:   fmt.Sprintf("%d / %d CZK", t.paid, t.expected),
+			Status: status,
+		}
+	}
+
+	var credits, debts []Credit
+	for _, name := range juniorNames {
+		bal := settledBalance(result.Members[name], currentMonth)
+		if bal > 0 {
+			credits = append(credits, Credit{Name: name, Amount: bal})
+		} else if bal < 0 {
+			debts = append(debts, Credit{Name: name, Amount: -bal})
+		}
+	}
+	sort.Slice(credits, func(i, j int) bool { return credits[i].Name < credits[j].Name })
+	sort.Slice(debts, func(i, j int) bool { return debts[i].Name < debts[j].Name })
+
+	// member_data: full reconcile output for all junior members.
+	memberData := make(map[string]JuniorsMemberData, len(result.Members))
+	for name, mr := range result.Members {
+		months := make(map[string]JuniorsMonthData, len(mr.Months))
+		for m, md := range mr.Months {
+			var exc *ExceptionData
+			if md.Exception != nil {
+				exc = &ExceptionData{Amount: md.Exception.Amount, Note: md.Exception.Note}
+			}
+			txEntries := make([]MemberTxEntry, len(md.Transactions))
+			for i, te := range md.Transactions {
+				txEntries[i] = memberTxFromDomain(te)
+			}
+			months[m] = JuniorsMonthData{
+				Expected:         juniorExpected(md),
+				OriginalExpected: juniorOriginalExpected(md),
+				AttendanceCount:  md.AttendanceCount,
+				Exception:        exc,
+				Paid:             md.Paid,
+				Transactions:     txEntries,
+			}
+		}
+		otherTxs := make([]MemberOtherEntry, len(mr.OtherTransactions))
+		for i, oe := range mr.OtherTransactions {
+			otherTxs[i] = memberOtherFromDomain(oe)
+		}
+		memberData[name] = JuniorsMemberData{
+			Tier:              mr.Tier,
+			Months:            months,
+			OtherTransactions: otherTxs,
+			TotalBalance:      mr.TotalBalance,
+		}
+	}
+
+	unmatched := make([]RawTransaction, len(result.Unmatched))
+	for i, tx := range result.Unmatched {
+		unmatched[i] = rawTxFromDomain(tx)
+	}
+
+	juniorURL := "https://docs.google.com/spreadsheets/d/" + config.AttendanceSheetID +
+		"/edit#gid=" + config.JuniorSheetGID
+
+	return JuniorsResponse{
+		Months:        labelsForMonths(sortedMonths, monthLabels),
+		RawMonths:     sortedMonths,
+		Results:       ensureSlice(results),
+		Totals:        totalsCells,
+		MemberData:    memberData,
+		MonthLabels:   monthLabels,
+		RawPayments:   groupRawPaymentsByPerson(txns, allNames),
+		Credits:       ensureSlice(credits),
+		Debts:         ensureSlice(debts),
+		Unmatched:     unmatched,
+		AttendanceURL: juniorURL,
+		PaymentsURL:   "https://docs.google.com/spreadsheets/d/" + config.PaymentsSheetID + "/edit",
+		BankAccount:   cfg.BankAccount,
+		CurrentMonth:  currentMonth,
+	}
+}
+
+func buildJuniorMemberRow(
+	name string,
+	mr domreconcile.MemberResult,
+	sortedMonths []string,
+	monthLabels map[string]string,
+	currentMonth string,
+	monthlyTotals map[string]*monthSums,
+) (row MemberRow, unpaidMonths, rawUnpaidMonths []string) {
+	row = MemberRow{Name: name}
+	for _, m := range sortedMonths {
+		md, ok := mr.Months[m]
+		if !ok {
+			md = domreconcile.MonthData{}
+		}
+		paid := int(md.Paid)
+
+		// Update monthly totals (skip "?" months for expected).
+		if t := monthlyTotals[m]; t != nil {
+			if !md.IsUnknown {
+				t.expected += md.Expected
+			}
+			t.paid += paid
+		}
+
+		// Attendance breakdown string e.g. ":3J,2A".
+		var breakdown string
+		jc, ac := md.JuniorAttendance, md.AdultAttendance
+		switch {
+		case jc > 0 && ac > 0:
+			breakdown = fmt.Sprintf(":%dJ,%dA", jc, ac)
+		case jc > 0:
+			breakdown = fmt.Sprintf(":%dJ", jc)
+		case ac > 0:
+			breakdown = fmt.Sprintf(":%dA", ac)
+		}
+		countStr := ""
+		if md.AttendanceCount > 0 {
+			countStr = fmt.Sprintf(" (%d%s)", md.AttendanceCount, breakdown)
+		}
+
+		// Fee display string.
+		var feeDisplay string
+		var isOverridden bool
+		if md.Exception != nil {
+			overrideAmount := md.Exception.Amount
+			var origStr string
+			if md.IsUnknown {
+				origStr = "?"
+				isOverridden = true
+			} else {
+				origStr = strconv.Itoa(md.OriginalExpected)
+				isOverridden = overrideAmount != md.OriginalExpected
+			}
+			if isOverridden {
+				feeDisplay = fmt.Sprintf("%d (%s) CZK%s", overrideAmount, origStr, countStr)
+			} else {
+				feeDisplay = fmt.Sprintf("%d CZK%s", md.Expected, countStr)
+			}
+		} else {
+			if md.IsUnknown {
+				feeDisplay = "? CZK" + countStr
+			} else {
+				feeDisplay = fmt.Sprintf("%d CZK%s", md.Expected, countStr)
+			}
+		}
+
+		status := "empty"
+		cellText := "-"
+		amountToPay := 0
+
+		switch {
+		case md.IsUnknown:
+			cellText = "?" + countStr
+		case md.Expected > 0:
+			switch {
+			case paid >= md.Expected:
+				status = "ok"
+				cellText = fmt.Sprintf("%d/%s", paid, feeDisplay)
+			case paid > 0:
+				status = "partial"
+				cellText = fmt.Sprintf("%d/%s", paid, feeDisplay)
+				amountToPay = md.Expected - paid
+				if m < currentMonth {
+					unpaidMonths = append(unpaidMonths, monthLabels[m])
+					rawUnpaidMonths = append(rawUnpaidMonths, rawMonthLabel(m))
+				}
+			default:
+				status = "unpaid"
+				cellText = fmt.Sprintf("0/%s", feeDisplay)
+				amountToPay = md.Expected
+				if m < currentMonth {
+					unpaidMonths = append(unpaidMonths, monthLabels[m])
+					rawUnpaidMonths = append(rawUnpaidMonths, rawMonthLabel(m))
+				}
+			}
+		case paid > 0:
+			status = "surplus"
+			cellText = fmt.Sprintf("PAID %d", paid)
+		}
+
+		tooltip := ""
+		if (!md.IsUnknown && md.Expected > 0) || paid > 0 {
+			tooltip = fmt.Sprintf("Received: %d, Expected: %d", paid, md.Expected)
+		}
+
+		row.Months = append(row.Months, MonthCell{
+			Text:       cellText,
+			Overridden: isOverridden,
+			Status:     status,
+			Amount:     amountToPay,
+			Month:      monthLabels[m],
+			RawMonth:   m,
+			Tooltip:    tooltip,
+		})
+	}
+	return row, unpaidMonths, rawUnpaidMonths
+}
+
+// juniorExpected converts domain MonthData to the Expected wire type.
+// When an exception exists it always produces a concrete int; otherwise
+// the "?" sentinel is used when IsUnknown=true.
+func juniorExpected(md domreconcile.MonthData) Expected {
+	if md.Exception == nil && md.IsUnknown {
+		return Expected{Unknown: true}
+	}
+	return Expected{Value: md.Expected}
+}
+
+// juniorOriginalExpected converts the original (pre-exception) expected fee.
+func juniorOriginalExpected(md domreconcile.MonthData) Expected {
+	if md.IsUnknown {
+		return Expected{Unknown: true}
+	}
+	return Expected{Value: md.OriginalExpected}
+}

go/internal/web/api/build_payments.go

@@ -0,0 +1,44 @@
+package api
+
+import (
+	"fuj-management/go/internal/config"
+	"sort"
+	"strings"
+
+	domreconcile "fuj-management/go/internal/domain/reconcile"
+)
+
+// buildPaymentsResponse constructs the PaymentsResponse wire type.
+// Mirrors scripts/views.py:build_payments_view_model.
+func buildPaymentsResponse(
+	txns []domreconcile.Transaction,
+	memberNames []string,
+) PaymentsResponse {
+	grouped := groupRawPaymentsByPerson(txns, memberNames)
+
+	// Add unmatched/unknown bucket for transactions with no person set.
+	const unknownKey = "Unmatched / Unknown"
+	for _, tx := range txns {
+		if strings.TrimSpace(tx.Person) == "" {
+			grouped[unknownKey] = append(grouped[unknownKey], rawTxFromDomain(tx))
+		}
+	}
+	// Sort the unknown bucket newest-first (others are sorted in groupRawPaymentsByPerson).
+	if rows, ok := grouped[unknownKey]; ok {
+		sort.Slice(rows, func(i, j int) bool { return rows[i].Date > rows[j].Date })
+		grouped[unknownKey] = rows
+	}
+
+	sortedPeople := make([]string, 0, len(grouped))
+	for p := range grouped {
+		sortedPeople = append(sortedPeople, p)
+	}
+	sort.Strings(sortedPeople)
+
+	return PaymentsResponse{
+		GroupedPayments: grouped,
+		SortedPeople:    sortedPeople,
+		AttendanceURL:   "https://docs.google.com/spreadsheets/d/" + config.AttendanceSheetID + "/edit",
+		PaymentsURL:     "https://docs.google.com/spreadsheets/d/" + config.PaymentsSheetID + "/edit",
+	}
+}

go/internal/web/api/handler.go

@@ -0,0 +1,155 @@
+package api
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"fuj-management/go/internal/config"
+	"fuj-management/go/internal/services/membership"
+	"log/slog"
+	"net/http"
+	"time"
+
+	domreconcile "fuj-management/go/internal/domain/reconcile"
+)
+
+// Handler holds the shared dependencies for all /api/* routes.
+type Handler struct {
+	BuildVersion string
+	BuildCommit  string
+	BuildDate    string
+	Sources      membership.Sources
+	Config       config.Config
+	Logger       *slog.Logger
+}
+
+// FlushCache invalidates all cached data via the underlying Sources.
+func (h *Handler) FlushCache() (int, error) { return h.Sources.FlushCache() }
+
+// ServeVersion handles GET /api/version.
+func (h *Handler) ServeVersion(w http.ResponseWriter, r *http.Request) {
+	writeJSON(w, VersionResponse{
+		Tag:       h.BuildVersion,
+		Commit:    h.BuildCommit,
+		BuildDate: h.BuildDate,
+	})
+}
+
+// ServeAdults handles GET /api/adults.
+func (h *Handler) ServeAdults(w http.ResponseWriter, r *http.Request) {
+	resp, err := h.AssembleAdults(r.Context())
+	if err != nil {
+		h.writeError(w, r, err)
+		return
+	}
+	writeJSON(w, resp)
+}
+
+// AssembleAdults loads all data and builds the adults view model.
+// Shared between the JSON API route and the HTML handler.
+func (h *Handler) AssembleAdults(ctx context.Context) (AdultsResponse, error) {
+	members, sortedMonths, txns, exceptions, err := h.loadAll(ctx, true)
+	if err != nil {
+		return AdultsResponse{}, err
+	}
+	result := domreconcile.Reconcile(members, sortedMonths, txns, exceptions, time.Now().Year())
+	return buildAdultsResponse(members, sortedMonths, result, txns, h.Config, time.Now().Format("2006-01")), nil
+}
+
+// ServeJuniors handles GET /api/juniors.
+func (h *Handler) ServeJuniors(w http.ResponseWriter, r *http.Request) {
+	resp, err := h.AssembleJuniors(r.Context())
+	if err != nil {
+		h.writeError(w, r, err)
+		return
+	}
+	writeJSON(w, resp)
+}
+
+// AssembleJuniors loads all data and builds the juniors view model.
+// Shared between the JSON API route and the HTML handler.
+func (h *Handler) AssembleJuniors(ctx context.Context) (JuniorsResponse, error) {
+	members, sortedMonths, txns, exceptions, err := h.loadAll(ctx, false)
+	if err != nil {
+		return JuniorsResponse{}, err
+	}
+	result := domreconcile.Reconcile(members, sortedMonths, txns, exceptions, time.Now().Year())
+	return buildJuniorsResponse(members, sortedMonths, result, txns, h.Config, time.Now().Format("2006-01")), nil
+}
+
+// ServePayments handles GET /api/payments.
+func (h *Handler) ServePayments(w http.ResponseWriter, r *http.Request) {
+	resp, err := h.AssemblePayments(r.Context())
+	if err != nil {
+		h.writeError(w, r, err)
+		return
+	}
+	writeJSON(w, resp)
+}
+
+// AssemblePayments loads transactions and builds the payments view model.
+// Shared between the JSON API route and the HTML handler.
+func (h *Handler) AssemblePayments(ctx context.Context) (PaymentsResponse, error) {
+	txns, err := h.Sources.LoadTransactions(ctx)
+	if err != nil {
+		return PaymentsResponse{}, fmt.Errorf("load transactions: %w", err)
+	}
+	return buildPaymentsResponse(txns, h.allMemberNames(ctx)), nil
+}
+
+func (h *Handler) loadAll(ctx context.Context, adults bool) (
+	members []domreconcile.Member,
+	sortedMonths []string,
+	txns []domreconcile.Transaction,
+	exceptions map[domreconcile.ExceptionKey]domreconcile.Exception,
+	err error,
+) {
+	if adults {
+		members, sortedMonths, err = h.Sources.LoadAdults(ctx)
+	} else {
+		members, sortedMonths, err = h.Sources.LoadJuniors(ctx)
+	}
+	if err != nil {
+		err = fmt.Errorf("load members: %w", err)
+		return
+	}
+	txns, err = h.Sources.LoadTransactions(ctx)
+	if err != nil {
+		err = fmt.Errorf("load transactions: %w", err)
+		return
+	}
+	exceptions, err = h.Sources.LoadExceptions(ctx)
+	if err != nil {
+		err = fmt.Errorf("load exceptions: %w", err)
+	}
+	return
+}
+
+func (h *Handler) allMemberNames(ctx context.Context) []string {
+	var names []string
+	if adults, _, err := h.Sources.LoadAdults(ctx); err == nil {
+		for _, m := range adults {
+			names = append(names, m.Name)
+		}
+	}
+	if juniors, _, err := h.Sources.LoadJuniors(ctx); err == nil {
+		for _, m := range juniors {
+			names = append(names, m.Name)
+		}
+	}
+	return names
+}
+
+func (h *Handler) writeError(w http.ResponseWriter, r *http.Request, err error) {
+	if h.Logger != nil {
+		h.Logger.Error("api error", "path", r.URL.Path, "err", err)
+	}
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.WriteHeader(http.StatusInternalServerError)
+	_ = json.NewEncoder(w).Encode(map[string]string{"error": err.Error()})
+}
+
+func writeJSON(w http.ResponseWriter, v any) {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	_ = json.NewEncoder(w).Encode(v)
+}

go/internal/web/api/juniors.go

@@ -0,0 +1,41 @@
+package api
+
+// JuniorsMonthData is the reconciled ledger for one junior member in one month.
+// expected and original_expected may be the "?" sentinel (single-attendance month
+// requiring manual review); they are carried via the Expected type.
+type JuniorsMonthData struct {
+	Expected         Expected        `json:"expected"`
+	OriginalExpected Expected        `json:"original_expected"`
+	AttendanceCount  int             `json:"attendance_count"`
+	Exception        *ExceptionData  `json:"exception"`
+	Paid             float64         `json:"paid"`
+	Transactions     []MemberTxEntry `json:"transactions"`
+}
+
+// JuniorsMemberData is the reconciled ledger for one junior member.
+type JuniorsMemberData struct {
+	Tier              string                      `json:"tier"`
+	Months            map[string]JuniorsMonthData `json:"months"`
+	OtherTransactions []MemberOtherEntry          `json:"other_transactions"`
+	TotalBalance      int                         `json:"total_balance"`
+}
+
+// JuniorsResponse is the JSON contract for GET /api/juniors.
+// Same outer shape as AdultsResponse; differs in that member_data carries
+// Expected (int or "?") for expected/original_expected fields.
+type JuniorsResponse struct {
+	Months        []string                     `json:"months"`
+	RawMonths     []string                     `json:"raw_months"`
+	Results       []MemberRow                  `json:"results"`
+	Totals        []TotalCell                  `json:"totals"`
+	MemberData    map[string]JuniorsMemberData `json:"member_data"`
+	MonthLabels   map[string]string            `json:"month_labels"`
+	RawPayments   map[string][]RawTransaction  `json:"raw_payments"`
+	Credits       []Credit                     `json:"credits"`
+	Debts         []Credit                     `json:"debts"`
+	Unmatched     []RawTransaction             `json:"unmatched"`
+	AttendanceURL string                       `json:"attendance_url"`
+	PaymentsURL   string                       `json:"payments_url"`
+	BankAccount   string                       `json:"bank_account"`
+	CurrentMonth  string                       `json:"current_month"`
+}

go/internal/web/api/payments.go

@@ -0,0 +1,9 @@
+package api
+
+// PaymentsResponse is the JSON contract for GET /api/payments.
+type PaymentsResponse struct {
+	GroupedPayments map[string][]RawTransaction `json:"grouped_payments"` // person name → rows
+	SortedPeople    []string                    `json:"sorted_people"`
+	AttendanceURL   string                      `json:"attendance_url"`
+	PaymentsURL     string                      `json:"payments_url"`
+}

go/internal/web/api/schemagen_test.go

@@ -0,0 +1,81 @@
+package api
+
+// schemagen_test.go generates and golden-compares JSON Schema files for every
+// /api/X response type.
+//
+// Normal run (CI): go test ./internal/web/api/... — asserts schemas match committed files.
+// Regenerate:      go test -run TestGenerateSchemas -update ./internal/web/api/...
+
+import (
+	"encoding/json"
+	"flag"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/invopop/jsonschema"
+)
+
+var updateFlag = flag.Bool("update", false, "overwrite api-schema fixture files with freshly generated schemas")
+
+// JSONSchema makes Expected self-describing for the reflector at test time.
+// The method is in a test file and is not compiled into production binaries.
+// It emits oneOf [integer, "?"] to match the custom MarshalJSON behaviour.
+func (Expected) JSONSchema() *jsonschema.Schema {
+	return &jsonschema.Schema{
+		OneOf: []*jsonschema.Schema{
+			{Type: "integer"},
+			{Enum: []any{"?"}},
+		},
+	}
+}
+
+func TestGenerateSchemas(t *testing.T) {
+	r := &jsonschema.Reflector{
+		AllowAdditionalProperties: false,
+	}
+
+	cases := []struct {
+		name string
+		val  any
+	}{
+		{"adults", &AdultsResponse{}},
+		{"juniors", &JuniorsResponse{}},
+		{"payments", &PaymentsResponse{}},
+		{"version", &VersionResponse{}},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			schema := r.Reflect(tc.val)
+
+			got, err := json.MarshalIndent(schema, "", "  ")
+			if err != nil {
+				t.Fatalf("marshal schema: %v", err)
+			}
+			got = append(got, '\n')
+
+			// Path: go/internal/web/api/ → ../../.. → go/ → tests/fixtures/api-schema/
+			path := filepath.Join("..", "..", "..", "tests", "fixtures", "api-schema", tc.name+".schema.json")
+
+			if *updateFlag {
+				if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+					t.Fatalf("mkdir: %v", err)
+				}
+				if err := os.WriteFile(path, got, 0o644); err != nil {
+					t.Fatalf("write schema: %v", err)
+				}
+				t.Logf("wrote %s", path)
+				return
+			}
+
+			want, err := os.ReadFile(path)
+			if err != nil {
+				t.Fatalf("read fixture %s: %v (re-run with -update to generate)", path, err)
+			}
+			if string(got) != string(want) {
+				t.Errorf("schema mismatch for %s; re-run with -update to regenerate", tc.name)
+			}
+		})
+	}
+}

go/internal/web/api/types.go

@@ -0,0 +1,122 @@
+// Package api defines wire types for the JSON API contract (/api/...).
+// These structs have explicit json: tags matching the Python view-model dict
+// keys so that M5 parity tests can do byte-equal comparison between backends.
+//
+// The three Python template-only JSON-string fields (member_data,
+// month_labels_json, raw_payments_json) are represented here as nested objects;
+// the Python /api/X shadow endpoint strips the json.dumps wrappers before
+// serialising.
+package api
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+// Expected holds a junior fee expectation: either a concrete integer or the
+// "?" sentinel (single-attendance month requiring manual review).
+// MarshalJSON emits the integer or the JSON string "?".
+type Expected struct {
+	Value   int
+	Unknown bool
+}
+
+func (e Expected) MarshalJSON() ([]byte, error) {
+	if e.Unknown {
+		return []byte(`"?"`), nil
+	}
+	return json.Marshal(e.Value)
+}
+
+func (e *Expected) UnmarshalJSON(data []byte) error {
+	if len(data) > 0 && data[0] == '"' {
+		var s string
+		if err := json.Unmarshal(data, &s); err != nil {
+			return err
+		}
+		if s == "?" {
+			e.Unknown = true
+			return nil
+		}
+		return fmt.Errorf("api.Expected: unexpected string %q", s)
+	}
+	e.Unknown = false
+	return json.Unmarshal(data, &e.Value)
+}
+
+// ExceptionData is a manual fee override for one member in one month.
+type ExceptionData struct {
+	Amount int    `json:"amount"`
+	Note   string `json:"note"`
+}
+
+// MemberTxEntry is one payment allocation to a member+month, as stored in
+// member_data.months[YYYY-MM].transactions.
+type MemberTxEntry struct {
+	Amount     float64 `json:"amount"`
+	Date       string  `json:"date"`
+	Sender     string  `json:"sender"`
+	Message    string  `json:"message"`
+	Confidence string  `json:"confidence"`
+}
+
+// MemberOtherEntry is an "other:…" purpose payment allocated to a member.
+type MemberOtherEntry struct {
+	Amount     float64 `json:"amount"`
+	Date       string  `json:"date"`
+	Sender     string  `json:"sender"`
+	Message    string  `json:"message"`
+	Purpose    string  `json:"purpose"`
+	Confidence string  `json:"confidence"`
+}
+
+// RawTransaction is a full payments-sheet row.
+// Used for unmatched transactions and raw_payments groupings.
+// Columns match the sheet layout: Date|Amount|manual fix|Person|Purpose|
+// Inferred Amount|Sender|VS|Message|Bank ID|Sync ID.
+type RawTransaction struct {
+	Date           string  `json:"date"`
+	Amount         float64 `json:"amount"`
+	ManualFix      string  `json:"manual_fix"`
+	Person         string  `json:"person"`
+	Purpose        string  `json:"purpose"`
+	InferredAmount float64 `json:"inferred_amount"`
+	Sender         string  `json:"sender"`
+	VS             string  `json:"vs"`
+	Message        string  `json:"message"`
+	BankID         string  `json:"bank_id"`
+	SyncID         string  `json:"sync_id"`
+}
+
+// MonthCell is one cell in a member's month column on the dashboard.
+type MonthCell struct {
+	Text       string `json:"text"`
+	Overridden bool   `json:"overridden"`
+	Status     string `json:"status"` // "empty"|"ok"|"partial"|"unpaid"|"surplus"
+	Amount     int    `json:"amount"`
+	Month      string `json:"month"`     // display label, e.g. "Apr+May 2025"
+	RawMonth   string `json:"raw_month"` // "YYYY-MM"
+	Tooltip    string `json:"tooltip"`
+}
+
+// TotalCell is one cell in the monthly totals row.
+type TotalCell struct {
+	Text   string `json:"text"`
+	Status string `json:"status"`
+}
+
+// MemberRow is one member's summary row in the dashboard results table.
+type MemberRow struct {
+	Name             string      `json:"name"`
+	Months           []MonthCell `json:"months"`
+	Balance          int         `json:"balance"`
+	UnpaidPeriods    string      `json:"unpaid_periods"`
+	RawUnpaidPeriods string      `json:"raw_unpaid_periods"`
+	PayableAmount    int         `json:"payable_amount"`
+}
+
+// Credit is one entry in the credits or debts lists.
+type Credit struct {
+	Name   string `json:"name"`
+	Amount int    `json:"amount"`
+}

go/internal/web/api/version.go

@@ -0,0 +1,9 @@
+package api
+
+// VersionResponse is the JSON contract for GET /api/version.
+// Keys match Python's BUILD_META dict (see app.py).
+type VersionResponse struct {
+	Tag       string `json:"tag"`
+	Commit    string `json:"commit"`
+	BuildDate string `json:"build_date"`
+}

go/internal/web/assets.go

@@ -0,0 +1,9 @@
+package web
+
+import "embed"
+
+//go:embed templates
+var templateFS embed.FS
+
+//go:embed static
+var staticFS embed.FS

go/internal/web/assets_test.go

@@ -0,0 +1,93 @@
+package web
+
+import (
+	"io/fs"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"strings"
+	"testing"
+)
+
+// TestEmbedCompleteness guards against a new template or static file being
+// added to disk but missing from the embedded FS (e.g. a new directory that
+// the //go:embed glob does not match).
+func TestEmbedCompleteness(t *testing.T) {
+	cases := []struct {
+		name      string
+		diskDir   string
+		embedFS   fs.FS
+		embedRoot string
+	}{
+		{"templates", "templates", templateFS, "templates"},
+		{"static", "static", staticFS, "static"},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			diskFS := os.DirFS(tc.diskDir)
+			_ = fs.WalkDir(diskFS, ".", func(path string, d fs.DirEntry, err error) error {
+				if err != nil || d.IsDir() {
+					return err
+				}
+				embPath := tc.embedRoot + "/" + path
+				if _, statErr := fs.Stat(tc.embedFS, embPath); statErr != nil {
+					t.Errorf("file %q exists on disk but is missing from embed.FS (%v)", embPath, statErr)
+				}
+				return nil
+			})
+		})
+	}
+}
+
+// TestStaticAssetsServed verifies that /static/* is served from the embedded
+// FS through the same mux wiring used in server.go, so a standalone binary
+// with no adjacent static/ directory still delivers assets.
+func TestStaticAssetsServed(t *testing.T) {
+	subFS, err := fs.Sub(staticFS, "static")
+	if err != nil {
+		t.Fatalf("fs.Sub static: %v", err)
+	}
+	mux := http.NewServeMux()
+	mux.Handle("/static/", http.StripPrefix("/static/", http.FileServerFS(subFS)))
+
+	cases := []struct {
+		path        string
+		wantCT      string
+		wantSnippet string
+	}{
+		{"/static/css/app.css", "text/css", "body {"},
+		{"/static/js/member-detail.js", "javascript", "Member-detail modal"},
+		{"/static/js/filters.js", "javascript", ""},
+		{"/static/js/payment-qr.js", "javascript", ""},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.path, func(t *testing.T) {
+			req := httptest.NewRequest(http.MethodGet, tc.path, nil)
+			w := httptest.NewRecorder()
+			mux.ServeHTTP(w, req)
+
+			if w.Code != http.StatusOK {
+				t.Fatalf("GET %s: status %d, want 200", tc.path, w.Code)
+			}
+			ct := w.Header().Get("Content-Type")
+			if !strings.Contains(ct, tc.wantCT) {
+				t.Errorf("GET %s: Content-Type %q, want it to contain %q", tc.path, ct, tc.wantCT)
+			}
+			if tc.wantSnippet != "" && !strings.Contains(w.Body.String(), tc.wantSnippet) {
+				t.Errorf("GET %s: body missing expected snippet %q", tc.path, tc.wantSnippet)
+			}
+		})
+	}
+
+	// Sanity: unknown path → 404 (file server doesn't fall through silently)
+	t.Run("missing-file", func(t *testing.T) {
+		req := httptest.NewRequest(http.MethodGet, "/static/css/nonexistent.css", nil)
+		w := httptest.NewRecorder()
+		mux.ServeHTTP(w, req)
+		if w.Code != http.StatusNotFound {
+			t.Errorf("unknown static path: status %d, want 404", w.Code)
+		}
+	})
+}

go/internal/web/html_handler.go

@@ -0,0 +1,143 @@
+package web
+
+import (
+	"bytes"
+	"fmt"
+	"fuj-management/go/internal/web/api"
+	"net/http"
+	"runtime/debug"
+)
+
+// HTMLHandler serves the Go-native HTML frontend.
+type HTMLHandler struct {
+	renderer   *Renderer
+	build      BuildInfo
+	apiHandler *api.Handler
+	actions    ActionHandlers
+}
+
+// NewHTMLHandler constructs an HTMLHandler.
+func NewHTMLHandler(r *Renderer, b BuildInfo, ah *api.Handler, actions ActionHandlers) *HTMLHandler {
+	return &HTMLHandler{renderer: r, build: b, apiHandler: ah, actions: actions}
+}
+
+func (h *HTMLHandler) ServeAdults(w http.ResponseWriter, r *http.Request) {
+	data, err := h.apiHandler.AssembleAdults(r.Context())
+	if err != nil {
+		h.renderer.Render(w, "adults", AdultsPageData{
+			PageData: PageData{Active: "adults", Build: h.build},
+			Error:    err.Error(),
+		})
+		return
+	}
+	h.renderer.Render(w, "adults", AdultsPageData{
+		PageData: PageData{Active: "adults", Build: h.build},
+		Data:     data,
+	})
+}
+
+func (h *HTMLHandler) ServeJuniors(w http.ResponseWriter, r *http.Request) {
+	data, err := h.apiHandler.AssembleJuniors(r.Context())
+	if err != nil {
+		h.renderer.Render(w, "juniors", JuniorsPageData{
+			PageData: PageData{Active: "juniors", Build: h.build},
+			Error:    err.Error(),
+		})
+		return
+	}
+	h.renderer.Render(w, "juniors", JuniorsPageData{
+		PageData: PageData{Active: "juniors", Build: h.build},
+		Data:     data,
+	})
+}
+
+func (h *HTMLHandler) ServePayments(w http.ResponseWriter, r *http.Request) {
+	data, err := h.apiHandler.AssemblePayments(r.Context())
+	if err != nil {
+		h.renderer.Render(w, "payments", PaymentsPageData{
+			PageData: PageData{Active: "payments", Build: h.build},
+			Error:    err.Error(),
+		})
+		return
+	}
+	h.renderer.Render(w, "payments", PaymentsPageData{
+		PageData: PageData{Active: "payments", Build: h.build},
+		Data:     data,
+	})
+}
+
+// ServeSync handles GET /sync-bank: runs sync+infer+flush then renders the result.
+func (h *HTMLHandler) ServeSync(w http.ResponseWriter, r *http.Request) {
+	pd := PageData{Active: "sync", Build: h.build}
+
+	if h.actions.BankSync == nil {
+		h.renderer.Render(w, "sync", SyncPageData{
+			PageData: pd,
+			Output:   "Bank sync is not configured.",
+			Success:  false,
+		})
+		return
+	}
+
+	var buf bytes.Buffer
+	success := true
+	if err := h.actions.BankSync(r.Context(), &buf); err != nil {
+		fmt.Fprintf(&buf, "\nError: %s\n\nStack trace:\n%s", err.Error(), debug.Stack())
+		success = false
+	}
+
+	fmt.Fprintln(&buf, "\n=== Flush Cache ===")
+	n, err := h.apiHandler.FlushCache()
+	if err != nil {
+		fmt.Fprintf(&buf, "flush error: %s\n", err.Error())
+		success = false
+	} else {
+		fmt.Fprintf(&buf, "%d cache file(s) deleted.\n", n)
+	}
+
+	h.renderer.Render(w, "sync", SyncPageData{
+		PageData: pd,
+		Output:   buf.String(),
+		Success:  success,
+	})
+}
+
+// ServeFlushCacheGET handles GET /flush-cache: renders the confirmation form.
+func (h *HTMLHandler) ServeFlushCacheGET(w http.ResponseWriter, r *http.Request) {
+	h.renderer.Render(w, "flush_cache", FlushPageData{
+		PageData: PageData{Active: "flush", Build: h.build},
+	})
+}
+
+// ServeFlushCachePOST handles POST /flush-cache: flushes and re-renders with count.
+func (h *HTMLHandler) ServeFlushCachePOST(w http.ResponseWriter, r *http.Request) {
+	n, _ := h.apiHandler.FlushCache()
+	h.renderer.Render(w, "flush_cache", FlushPageData{
+		PageData: PageData{Active: "flush", Build: h.build},
+		Flushed:  true,
+		Deleted:  n,
+	})
+}
+
+// ServeQR handles GET /qr: generates and returns a Czech QR Platba PNG.
+func (h *HTMLHandler) ServeQR(w http.ResponseWriter, r *http.Request) {
+	q := r.URL.Query()
+	account := q.Get("account")
+	amount := q.Get("amount")
+	message := q.Get("message")
+	if account == "" {
+		account = h.apiHandler.Config.BankAccount
+	}
+	if amount == "" {
+		amount = "0"
+	}
+
+	payload := BuildSPD(account, amount, message, h.apiHandler.Config.BankAccount)
+	png, err := RenderQRCode(payload)
+	if err != nil {
+		http.Error(w, "qr encode: "+err.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Type", "image/png")
+	_, _ = w.Write(png)
+}

go/internal/web/html_handler_test.go

@@ -0,0 +1,383 @@
+package web_test
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"fuj-management/go/internal/config"
+	"fuj-management/go/internal/domain/reconcile"
+	"fuj-management/go/internal/web"
+	"fuj-management/go/internal/web/api"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+// fixtureSources returns one adult ("Test Member", tier A) with a 2026-01 fee
+// of 750 CZK (4 sessions) and a matching payment of 750 — mirrors Python's
+// test_adults_route fixture.
+type fixtureSources struct{}
+
+func (fixtureSources) LoadAdults(_ context.Context) ([]reconcile.Member, []string, error) {
+	return []reconcile.Member{
+		{Name: "Test Member", Tier: "A", Fees: map[string]reconcile.FeeData{
+			"2026-01": {Expected: 750, Attendance: 4},
+		}},
+	}, []string{"2026-01"}, nil
+}
+
+func (fixtureSources) LoadJuniors(_ context.Context) ([]reconcile.Member, []string, error) {
+	return nil, nil, nil
+}
+
+func (fixtureSources) LoadTransactions(_ context.Context) ([]reconcile.Transaction, error) {
+	amt := float64(750)
+	return []reconcile.Transaction{
+		{Date: "2026-01-01", Amount: 750, Person: "Test Member", Purpose: "2026-01", InferredAmount: &amt},
+	}, nil
+}
+
+func (fixtureSources) LoadExceptions(_ context.Context) (map[reconcile.ExceptionKey]reconcile.Exception, error) {
+	return nil, nil
+}
+
+func (fixtureSources) FlushCache() (int, error) { return 0, nil }
+
+func fixtureHandler(t *testing.T) *api.Handler {
+	t.Helper()
+	return &api.Handler{
+		Sources: fixtureSources{},
+		Config:  config.Config{BankAccount: "CZ0000000000000000000000"},
+	}
+}
+
+func TestHTMLHandlerSmoke(t *testing.T) {
+	renderer, err := web.NewRenderer()
+	if err != nil {
+		t.Fatalf("NewRenderer: %v", err)
+	}
+	b := web.BuildInfo{Version: "v0", Commit: "abc1234", BuildDate: "2026-01-01"}
+	h := web.NewHTMLHandler(renderer, b, fixtureHandler(t), web.ActionHandlers{})
+
+	cases := []struct {
+		path    string
+		handler http.HandlerFunc
+	}{
+		{"/adults", h.ServeAdults},
+		{"/juniors", h.ServeJuniors},
+		{"/payments", h.ServePayments},
+		{"/sync-bank", h.ServeSync},
+		{"/flush-cache", h.ServeFlushCacheGET},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.path, func(t *testing.T) {
+			req := httptest.NewRequest(http.MethodGet, tc.path, nil)
+			w := httptest.NewRecorder()
+			tc.handler(w, req)
+
+			if w.Code != http.StatusOK {
+				t.Errorf("status = %d, want 200", w.Code)
+			}
+			if ct := w.Header().Get("Content-Type"); !strings.HasPrefix(ct, "text/html") {
+				t.Errorf("Content-Type = %q, want text/html", ct)
+			}
+
+			body := w.Body.String()
+			if n := strings.Count(body, `class="active"`); n != 1 {
+				t.Errorf(`class="active" count = %d, want 1`, n)
+			}
+			want := fmt.Sprintf(`href="%s" class="active"`, tc.path)
+			if !strings.Contains(body, want) {
+				t.Errorf("missing active link %q in body", want)
+			}
+		})
+	}
+}
+
+func TestAdultsPage(t *testing.T) {
+	renderer, err := web.NewRenderer()
+	if err != nil {
+		t.Fatalf("NewRenderer: %v", err)
+	}
+	b := web.BuildInfo{Version: "v0", Commit: "abc1234", BuildDate: "2026-01-01"}
+	h := web.NewHTMLHandler(renderer, b, fixtureHandler(t), web.ActionHandlers{})
+
+	req := httptest.NewRequest(http.MethodGet, "/adults", nil)
+	w := httptest.NewRecorder()
+	h.ServeAdults(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", w.Code)
+	}
+
+	body := w.Body.String()
+
+	for _, want := range []string{
+		"Adults Dashboard",
+		"Test Member",
+		"750/750 CZK (4)", // paid/expected (attendance)
+	} {
+		if !strings.Contains(body, want) {
+			t.Errorf("body missing %q", want)
+		}
+	}
+
+	// Python assertion: cell text never says literally "OK"
+	if strings.Contains(body, ">OK<") {
+		t.Error("body should not contain >OK<")
+	}
+}
+
+func TestModalMarkup(t *testing.T) {
+	renderer, err := web.NewRenderer()
+	if err != nil {
+		t.Fatalf("NewRenderer: %v", err)
+	}
+	b := web.BuildInfo{Version: "v0", Commit: "abc1234", BuildDate: "2026-01-01"}
+	h := web.NewHTMLHandler(renderer, b, fixtureHandler(t), web.ActionHandlers{})
+
+	cases := []struct {
+		path    string
+		handler http.HandlerFunc
+		page    string
+		wantRow string // data-name present only when the page has rows
+	}{
+		{"/adults", h.ServeAdults, "adults", `data-name="Test Member"`},
+		{"/juniors", h.ServeJuniors, "juniors", ""},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.path, func(t *testing.T) {
+			req := httptest.NewRequest(http.MethodGet, tc.path, nil)
+			w := httptest.NewRecorder()
+			tc.handler(w, req)
+			body := w.Body.String()
+
+			for _, want := range []string{
+				`data-page="` + tc.page + `"`,
+				`id="memberModal"`,
+				`/static/js/member-detail.js`,
+			} {
+				if !strings.Contains(body, want) {
+					t.Errorf("body missing %q", want)
+				}
+			}
+			if tc.wantRow != "" && !strings.Contains(body, tc.wantRow) {
+				t.Errorf("body missing info-icon row %q", tc.wantRow)
+			}
+		})
+	}
+}
+
+func TestPaymentsPage(t *testing.T) {
+	renderer, err := web.NewRenderer()
+	if err != nil {
+		t.Fatalf("NewRenderer: %v", err)
+	}
+	b := web.BuildInfo{Version: "v0", Commit: "abc1234", BuildDate: "2026-01-01"}
+	h := web.NewHTMLHandler(renderer, b, fixtureHandler(t), web.ActionHandlers{})
+
+	req := httptest.NewRequest(http.MethodGet, "/payments", nil)
+	w := httptest.NewRecorder()
+	h.ServePayments(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", w.Code)
+	}
+
+	body := w.Body.String()
+
+	for _, want := range []string{
+		"Payments Ledger",
+		"<h2>Test Member</h2>",
+		"750 CZK",
+		"2026-01-01",
+		"2026-01",
+	} {
+		if !strings.Contains(body, want) {
+			t.Errorf("body missing %q", want)
+		}
+	}
+}
+
+func TestServeQR(t *testing.T) {
+	renderer, err := web.NewRenderer()
+	if err != nil {
+		t.Fatalf("NewRenderer: %v", err)
+	}
+	b := web.BuildInfo{Version: "v0", Commit: "abc1234", BuildDate: "2026-01-01"}
+	h := web.NewHTMLHandler(renderer, b, fixtureHandler(t), web.ActionHandlers{})
+
+	req := httptest.NewRequest(http.MethodGet, "/qr?account=2702008874%2F2010&amount=700&message=Test", nil)
+	w := httptest.NewRecorder()
+	h.ServeQR(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", w.Code)
+	}
+	if ct := w.Header().Get("Content-Type"); ct != "image/png" {
+		t.Errorf("Content-Type = %q, want image/png", ct)
+	}
+	// PNG magic bytes: \x89PNG\r\n\x1a\n
+	magic := []byte{0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a}
+	body := w.Body.Bytes()
+	if len(body) < len(magic) || !bytes.Equal(body[:len(magic)], magic) {
+		t.Error("response body does not start with PNG magic bytes")
+	}
+}
+
+func TestServeFlushCacheGET(t *testing.T) {
+	renderer, err := web.NewRenderer()
+	if err != nil {
+		t.Fatalf("NewRenderer: %v", err)
+	}
+	b := web.BuildInfo{Version: "v0", Commit: "abc1234", BuildDate: "2026-01-01"}
+	h := web.NewHTMLHandler(renderer, b, fixtureHandler(t), web.ActionHandlers{})
+
+	req := httptest.NewRequest(http.MethodGet, "/flush-cache", nil)
+	w := httptest.NewRecorder()
+	h.ServeFlushCacheGET(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", w.Code)
+	}
+	body := w.Body.String()
+	if !strings.Contains(body, "Flush Cache") {
+		t.Error("body missing Flush Cache heading")
+	}
+	if strings.Contains(body, "file(s) deleted") {
+		t.Error("GET should not show deleted count")
+	}
+}
+
+func TestServeFlushCachePOST(t *testing.T) {
+	renderer, err := web.NewRenderer()
+	if err != nil {
+		t.Fatalf("NewRenderer: %v", err)
+	}
+	b := web.BuildInfo{Version: "v0", Commit: "abc1234", BuildDate: "2026-01-01"}
+	h := web.NewHTMLHandler(renderer, b, fixtureHandler(t), web.ActionHandlers{})
+
+	req := httptest.NewRequest(http.MethodPost, "/flush-cache", nil)
+	w := httptest.NewRecorder()
+	h.ServeFlushCachePOST(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", w.Code)
+	}
+	body := w.Body.String()
+	// fixtureSources.FlushCache returns 0
+	if !strings.Contains(body, "file(s) deleted") {
+		t.Error("POST should show deleted count")
+	}
+}
+
+func TestServeSync(t *testing.T) {
+	renderer, err := web.NewRenderer()
+	if err != nil {
+		t.Fatalf("NewRenderer: %v", err)
+	}
+	b := web.BuildInfo{Version: "v0", Commit: "abc1234", BuildDate: "2026-01-01"}
+
+	actions := web.ActionHandlers{
+		BankSync: func(_ context.Context, out io.Writer) error {
+			fmt.Fprintln(out, "=== Sync Fio Transactions ===")
+			fmt.Fprintln(out, "Synced 3 new transaction(s).")
+			fmt.Fprintln(out, "=== Infer Payments ===")
+			fmt.Fprintln(out, "Inferred 2 row(s).")
+			return nil
+		},
+	}
+	h := web.NewHTMLHandler(renderer, b, fixtureHandler(t), actions)
+
+	req := httptest.NewRequest(http.MethodGet, "/sync-bank", nil)
+	w := httptest.NewRecorder()
+	h.ServeSync(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", w.Code)
+	}
+	body := w.Body.String()
+	for _, want := range []string{
+		"Sync Bank Data",
+		"Synced 3 new transaction(s).",
+		"Inferred 2 row(s).",
+		"Flush Cache",
+	} {
+		if !strings.Contains(body, want) {
+			t.Errorf("body missing %q", want)
+		}
+	}
+}
+
+func TestPaymentQRMarkup(t *testing.T) {
+	renderer, err := web.NewRenderer()
+	if err != nil {
+		t.Fatalf("NewRenderer: %v", err)
+	}
+	b := web.BuildInfo{Version: "v0", Commit: "abc1234", BuildDate: "2026-01-01"}
+	h := web.NewHTMLHandler(renderer, b, fixtureHandler(t), web.ActionHandlers{})
+
+	cases := []struct {
+		path    string
+		handler http.HandlerFunc
+	}{
+		{"/adults", h.ServeAdults},
+		{"/juniors", h.ServeJuniors},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.path, func(t *testing.T) {
+			req := httptest.NewRequest(http.MethodGet, tc.path, nil)
+			w := httptest.NewRecorder()
+			tc.handler(w, req)
+			body := w.Body.String()
+
+			for _, want := range []string{
+				`id="qrModal"`,
+				`id="qrImg"`,
+				`id="qrTitle"`,
+				`id="qrAccount"`,
+				`id="qrAmount"`,
+				`id="qrMessage"`,
+				`/static/js/payment-qr.js`,
+				`data-bank-account="CZ0000000000000000000000"`,
+			} {
+				if !strings.Contains(body, want) {
+					t.Errorf("body missing %q", want)
+				}
+			}
+
+			// Pay buttons must use <button>, never a bare href to /qr.
+			if strings.Contains(body, `href="/qr`) {
+				t.Error("body must not contain href=/qr (Pay buttons should be <button>, not <a>)")
+			}
+		})
+	}
+}
+
+func TestServeVersion(t *testing.T) {
+	req := httptest.NewRequest(http.MethodGet, "/api/version", nil)
+	w := httptest.NewRecorder()
+	fixtureHandler(t).ServeVersion(w, req)
+
+	if w.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", w.Code)
+	}
+	if ct := w.Header().Get("Content-Type"); !strings.HasPrefix(ct, "application/json") {
+		t.Errorf("Content-Type = %q, want application/json", ct)
+	}
+	var raw map[string]json.RawMessage
+	if err := json.NewDecoder(w.Body).Decode(&raw); err != nil {
+		t.Fatalf("decode JSON: %v", err)
+	}
+	for _, key := range []string{"tag", "commit", "build_date"} {
+		if _, ok := raw[key]; !ok {
+			t.Errorf("JSON response missing key %q", key)
+		}
+	}
+}

go/internal/web/qr.go

@@ -0,0 +1,50 @@
+package web
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+	"unicode/utf8"
+
+	qrcode "github.com/skip2/go-qrcode"
+)
+
+var validAccount = regexp.MustCompile(`^[A-Z]{2}\d{2,34}$|^\d{1,16}/\d{4}$`)
+
+// BuildSPD builds a Czech QR Platba SPD string, matching Python's qr_code handler.
+// Invalid account falls back to defaultAccount.
+// Amount is clamped to [0, 10_000_000]; non-numeric input becomes "0.00".
+// Message is truncated to 60 runes and stripped of '*' characters.
+func BuildSPD(account, amount, message, defaultAccount string) string {
+	if !validAccount.MatchString(account) {
+		account = defaultAccount
+	}
+
+	var amtStr string
+	var f float64
+	if _, err := fmt.Sscanf(amount, "%f", &f); err != nil || f < 0 || f > 10_000_000 {
+		amtStr = "0.00"
+	} else {
+		amtStr = fmt.Sprintf("%.2f", f)
+	}
+
+	if utf8.RuneCountInString(message) > 60 {
+		runes := []rune(message)
+		message = string(runes[:60])
+	}
+	message = strings.ReplaceAll(message, "*", "")
+
+	var accStr string
+	if parts := strings.SplitN(account, "/", 2); len(parts) == 2 {
+		accStr = parts[0] + "*BC:" + parts[1]
+	} else {
+		accStr = account
+	}
+
+	return fmt.Sprintf("SPD*1.0*ACC:%s*AM:%s*CC:CZK*MSG:%s", accStr, amtStr, message)
+}
+
+// RenderQRCode encodes payload as a PNG QR code (256×256, error correction Medium).
+func RenderQRCode(payload string) ([]byte, error) {
+	return qrcode.Encode(payload, qrcode.Medium, 256)
+}

go/internal/web/qr_test.go

@@ -0,0 +1,91 @@
+package web
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestQRBuildSPD(t *testing.T) {
+	const def = "2702008874/2010"
+
+	cases := []struct {
+		name    string
+		account string
+		amount  string
+		message string
+		want    string
+	}{
+		{
+			name:    "czech account",
+			account: "2702008874/2010",
+			amount:  "700",
+			message: "Test Member: 01/2026",
+			want:    "SPD*1.0*ACC:2702008874*BC:2010*AM:700.00*CC:CZK*MSG:Test Member: 01/2026",
+		},
+		{
+			name:    "IBAN account",
+			account: "CZ6508000000192000145399",
+			amount:  "500",
+			message: "hi",
+			want:    "SPD*1.0*ACC:CZ6508000000192000145399*AM:500.00*CC:CZK*MSG:hi",
+		},
+		{
+			name:    "invalid account falls back to default",
+			account: "NOTANACCOUNT",
+			amount:  "100",
+			message: "x",
+			want:    "SPD*1.0*ACC:2702008874*BC:2010*AM:100.00*CC:CZK*MSG:x",
+		},
+		{
+			name:    "empty account falls back to default",
+			account: "",
+			amount:  "0",
+			message: "",
+			want:    "SPD*1.0*ACC:2702008874*BC:2010*AM:0.00*CC:CZK*MSG:",
+		},
+		{
+			name:    "negative amount clamped to 0.00",
+			account: def,
+			amount:  "-1",
+			message: "",
+			want:    "SPD*1.0*ACC:2702008874*BC:2010*AM:0.00*CC:CZK*MSG:",
+		},
+		{
+			name:    "amount over 10M clamped to 0.00",
+			account: def,
+			amount:  "99999999",
+			message: "",
+			want:    "SPD*1.0*ACC:2702008874*BC:2010*AM:0.00*CC:CZK*MSG:",
+		},
+		{
+			name:    "non-numeric amount becomes 0.00",
+			account: def,
+			amount:  "abc",
+			message: "",
+			want:    "SPD*1.0*ACC:2702008874*BC:2010*AM:0.00*CC:CZK*MSG:",
+		},
+		{
+			name:    "asterisks stripped from message",
+			account: def,
+			amount:  "100",
+			message: "pay*now",
+			want:    "SPD*1.0*ACC:2702008874*BC:2010*AM:100.00*CC:CZK*MSG:paynow",
+		},
+		{
+			name:    "message truncated to 60 runes",
+			account: def,
+			amount:  "0",
+			message: strings.Repeat("á", 65),
+			want:    "SPD*1.0*ACC:2702008874*BC:2010*AM:0.00*CC:CZK*MSG:" + strings.Repeat("á", 60),
+		},
+	}
+
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			got := BuildSPD(tc.account, tc.amount, tc.message, def)
+			if got != tc.want {
+				t.Errorf("\ngot:  %s\nwant: %s", got, tc.want)
+			}
+		})
+	}
+}

go/internal/web/render.go

@@ -0,0 +1,91 @@
+package web
+
+import (
+	"fmt"
+	"fuj-management/go/internal/web/api"
+	"html/template"
+	"log/slog"
+	"net/http"
+)
+
+// PageData is the view model passed to every HTML template.
+type PageData struct {
+	Active string
+	Build  BuildInfo
+}
+
+// AdultsPageData is the view model for the /adults HTML page.
+type AdultsPageData struct {
+	PageData
+	Data  api.AdultsResponse
+	Error string
+}
+
+// JuniorsPageData is the view model for the /juniors HTML page.
+type JuniorsPageData struct {
+	PageData
+	Data  api.JuniorsResponse
+	Error string
+}
+
+// PaymentsPageData is the view model for the /payments HTML page.
+type PaymentsPageData struct {
+	PageData
+	Data  api.PaymentsResponse
+	Error string
+}
+
+// SyncPageData is the view model for the /sync-bank HTML page.
+type SyncPageData struct {
+	PageData
+	Output  string
+	Success bool
+}
+
+// FlushPageData is the view model for the /flush-cache HTML page.
+type FlushPageData struct {
+	PageData
+	Flushed bool
+	Deleted int
+}
+
+// Renderer parses and executes HTML templates from the embedded FS.
+type Renderer struct {
+	tmpls map[string]*template.Template
+}
+
+var pageNames = []string{"adults", "juniors", "payments", "sync", "flush_cache"}
+
+var tmplFuncs = template.FuncMap{}
+
+// NewRenderer parses all templates from the embedded FS.
+// A parse failure should be treated as a startup-time fatal error.
+func NewRenderer() (*Renderer, error) {
+	tmpls := make(map[string]*template.Template, len(pageNames))
+	for _, name := range pageNames {
+		t, err := template.New("").Funcs(tmplFuncs).ParseFS(templateFS,
+			"templates/base.tmpl",
+			"templates/partials/nav.tmpl",
+			"templates/partials/footer.tmpl",
+			"templates/"+name+".tmpl",
+		)
+		if err != nil {
+			return nil, fmt.Errorf("parse template %q: %w", name, err)
+		}
+		tmpls[name] = t
+	}
+	return &Renderer{tmpls: tmpls}, nil
+}
+
+// Render executes the named template with data, writing to w.
+func (r *Renderer) Render(w http.ResponseWriter, name string, data any) {
+	t, ok := r.tmpls[name]
+	if !ok {
+		http.Error(w, "template not found: "+name, http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	if err := t.ExecuteTemplate(w, "base", data); err != nil {
+		slog.Error("render template", "name", name, "err", err)
+	}
+}

go/internal/web/server.go

@@ -1,8 +1,14 @@
 package web
 
 import (
+	"context"
 	"fmt"
+	"fuj-management/go/internal/config"
+	"fuj-management/go/internal/services/membership"
+	"fuj-management/go/internal/web/api"
 	"fuj-management/go/internal/web/middleware"
+	"io"
+	"io/fs"
 	"log/slog"
 	"net/http"
 )
@@ -14,19 +20,60 @@ type BuildInfo struct {
 	BuildDate string
 }
 
+// ActionHandlers holds function closures for side-effectful operations that
+// require dependencies (fio, sheets) not present on the core API handler.
+type ActionHandlers struct {
+	// BankSync runs sync+infer and writes a human-readable log to out.
+	// nil disables the /sync-bank action (renders an error instead).
+	BankSync func(ctx context.Context, out io.Writer) error
+}
+
 // Run registers routes and starts the HTTP server on addr.
-func Run(logger *slog.Logger, addr string, build BuildInfo) error {
+func Run(logger *slog.Logger, addr string, build BuildInfo, sources membership.Sources, cfg config.Config, actions ActionHandlers) error {
+	renderer, err := NewRenderer()
+	if err != nil {
+		return fmt.Errorf("init templates: %w", err)
+	}
+
+	ah := &api.Handler{
+		BuildVersion: build.Version,
+		BuildCommit:  build.Commit,
+		BuildDate:    build.BuildDate,
+		Sources:      sources,
+		Config:       cfg,
+		Logger:       logger,
+	}
+	hh := NewHTMLHandler(renderer, build, ah, actions)
+
+	staticSubFS, err := fs.Sub(staticFS, "static")
+	if err != nil {
+		return fmt.Errorf("static subfs: %w", err)
+	}
+
 	mux := http.NewServeMux()
-	mux.HandleFunc("GET /{$}", helloHandler(build))
+
+	// HTML routes
+	mux.HandleFunc("GET /{$}", func(w http.ResponseWriter, r *http.Request) {
+		http.Redirect(w, r, "/adults", http.StatusFound)
+	})
+	mux.HandleFunc("GET /adults", hh.ServeAdults)
+	mux.HandleFunc("GET /juniors", hh.ServeJuniors)
+	mux.HandleFunc("GET /payments", hh.ServePayments)
+	mux.HandleFunc("GET /sync-bank", hh.ServeSync)
+	mux.HandleFunc("GET /flush-cache", hh.ServeFlushCacheGET)
+	mux.HandleFunc("POST /flush-cache", hh.ServeFlushCachePOST)
+	mux.HandleFunc("GET /qr", hh.ServeQR)
+
+	// Static files
+	mux.Handle("/static/", http.StripPrefix("/static/", http.FileServerFS(staticSubFS)))
+
+	// JSON API routes
+	mux.HandleFunc("GET /api/version", ah.ServeVersion)
+	mux.HandleFunc("GET /version", ah.ServeVersion)
+	mux.HandleFunc("GET /api/adults", ah.ServeAdults)
+	mux.HandleFunc("GET /api/juniors", ah.ServeJuniors)
+	mux.HandleFunc("GET /api/payments", ah.ServePayments)
 
 	logger.Info("starting server", "addr", addr)
 	return http.ListenAndServe(addr, middleware.RequestTimer(logger, mux))
 }
-
-func helloHandler(build BuildInfo) http.HandlerFunc {
-	return func(w http.ResponseWriter, r *http.Request) {
-		w.Header().Set("Content-Type", "text/plain; charset=utf-8")
-		fmt.Fprintf(w, "fuj-go ok\nversion: %s\ncommit:  %s\nbuilt:   %s\n",
-			build.Version, build.Commit, build.BuildDate)
-	}
-}