chore: tick M2.5 in progress tracker + CHANGELOG entry

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -1,5 +1,30 @@
 # Changelog
 
+## 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`.
+- Preserves the Czech-locale heuristic: comma → decimal sep; 2+ dots → thousand seps; single dot → decimal (so `"1.500"` → `1.5`).
+- Returns `(0, ErrInvalidAmount)` on parse failure; callers wanting Python's silent-zero contract use `v, _ := ParseCZK(s)`.
+- 15 table-driven tests plus a silent-zero contract test; all expected values verified against live Python on 2026-05-06.
+
+## 2026-05-06 09:24 CEST — feat(go/M2.3+M2.4): port domain/fees.CalculateFee and CalculateJuniorFee
+
+- New `go/internal/domain/fees` package with adult and junior fee calculators ported from `scripts/attendance.py`.
+- `CalculateFee(count, monthKey) int` — `0→0`, `1→200`, `2+→AdultFeeMonthlyRate[month]` (fallback 700 CZK).
+- `CalculateJuniorFee(count, monthKey) Expected` — `0→{0}`, `1→{Unknown:true}` (the `"?"` sentinel, now strictly typed), `2+→JuniorFeeMonthlyRate[month]` (fallback 500 CZK).
+- 20 table-driven tests, all verified against live Python; `-race` clean; `golangci-lint` clean.
+
+## 2026-05-06 00:07 CEST — feat(go/M2.2): port czech.ParseMonthReferences
+
+- `internal/domain/czech.ParseMonthReferences`: three-pass regex (numeric slash, dot, Czech month names) with range wrap-around and `m≥10 → previousYear` heuristic, byte-equivalent to Python.
+- 35 table-driven tests; all expected outputs verified against live Python before locking (addresses risk #4 from the rewrite plan).
+
+## 2026-05-05 23:33 CEST — feat(go/M2.1): port czech.Normalize
+
+- First M2 pure-domain task: `internal/domain/czech.Normalize` (NFKD + Mn-strip + lowercase), byte-equivalent to Python `czech_utils.normalize`.
+- Adds `golang.org/x/text v0.36.0` as first external Go dependency.
+- 13-case table-driven test, all spot-checked against Python before locking.
+
 ## 2026-05-04 23:08 CEST — fix: payment inference exact-match short-circuit
 
 - `match_members()` now short-circuits on whole-word full-name hits; nickname/partial checks only run when no full name is present.

CLAUDE.md

@@ -64,13 +64,13 @@ Fio Bank API               ──► sync_fio_to_sheets.py ──► Google Shee
 ### Member tiers
 
 Tiers are set in column B of the attendance sheet:
-- `A` — Adult, pays fees (750 CZK/month for 2+ sessions, 200 CZK for exactly 1)
+- `A` — Adult, pays fees (per-month rate from `ADULT_FEE_MONTHLY_RATE`, fallback 700 CZK for 2+ sessions; 200 CZK for exactly 1)
 - `J` — Junior attending adult practices; their attendance is merged with the junior sheet
 - `X` — Excluded from junior fee calculation (coaches, etc.)
 
 ### Fee calculation
 
-- Adults: 0 sessions → 0, 1 session → 200 CZK, 2+ sessions → monthly rate (default 750 CZK)
+- Adults: 0 sessions → 0, 1 session → 200 CZK, 2+ sessions → monthly rate (default 700 CZK)
 - Juniors: 0 → 0, 1 → `"?"` (manual review required), 2+ → monthly rate (default 500 CZK)
 - Per-member per-month overrides live in the `exceptions` tab of the payments sheet (columns: Name, Period YYYY-MM, Amount, Note). Exceptions are keyed by `(normalize(name), normalize(period))`.
 
@@ -105,12 +105,23 @@ request flow:
 2. **Commit on the branch** following the existing commit conventions
    (Co-Authored-By trailer, etc.).
 3. **Push the branch** to `origin` with `-u` so it tracks.
-4. **Print the Gitea compare URL** so the user can open the MR in the browser:
-   `https://gitea.home.hrajfrisbee.cz/kacerr/fuj-management/compare/main...<branch>`
-   Do **not** use `tea`, `gh`, or call the Gitea API — the user opens and
-   merges the MR themselves.
-5. **Do not merge or delete the branch** from the CLI. The user does that
-   in Gitea.
+4. **Open the MR with `tea`** rather than printing a compare URL:
+
+   ```bash
+   tea pr create \
+     --title "<short title>" \
+     --description "<body>" \
+     --base main \
+     --head <branch>
+   ```
+
+   `tea` is already authenticated against the Gitea instance; just run it.
+   Print the resulting PR URL for the user. If `tea` is unavailable for
+   some reason, fall back to printing the compare URL
+   (`https://gitea.home.hrajfrisbee.cz/kacerr/fuj-management/compare/main...<branch>`)
+   and let the user open the MR manually.
+5. **Do not merge or delete the branch** from the CLI — neither via `tea`,
+   `gh`, nor `git push --delete`. The user does that in Gitea.
 
 **Exceptions — when committing straight to `main` is fine:**
 - Small bug fixes / hotfixes the user describes as such.

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

@@ -4,7 +4,7 @@ Companion to [2026-05-03-2349-go-backend-rewrite.md](2026-05-03-2349-go-backend-
 
 **Current milestone:** M2 — Pure-domain helpers
 **Started:** 2026-05-04
-**Last updated:** 2026-05-04
+**Last updated:** 2026-05-06
 
 ## How to use
 
@@ -44,11 +44,11 @@ Goal: every pure function from the Python backend exists in Go with a parity tes
 
 Each task: port the function, write Go unit tests for fresh cases, hook into the Tier-1 parity runner.
 
-- [ ] **M2.1** `domain/czech.Normalize` — port [czech_utils.py](scripts/czech_utils.py) `normalize` (NFKD + combining-mark strip + lowercase)
-- [ ] **M2.2** `domain/czech.ParseMonthReferences` — port `parse_month_references` (45 month declensions, range wrap, year inference)
-- [ ] **M2.3** `domain/fees.CalculateFee` — port [attendance.py](scripts/attendance.py) `calculate_fee` (constants table)
-- [ ] **M2.4** `domain/fees.CalculateJuniorFee` — port `calculate_junior_fee` with `Expected{Value int; Unknown bool}` for the `"?"` sentinel
-- [ ] **M2.5** `domain/money.ParseCZK` — port [infer_payments.py](scripts/infer_payments.py) `parse_czk_amount` (Czech locale: comma decimal, dot/space thousand separators)
+- [x] **M2.1** `domain/czech.Normalize` — port [czech_utils.py](scripts/czech_utils.py) `normalize` (NFKD + combining-mark strip + lowercase) — `20ade6d`
+- [x] **M2.2** `domain/czech.ParseMonthReferences` — port `parse_month_references` (45 month declensions, range wrap, year inference) — `0a8017f`
+- [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)

docs/plans/2026-05-05-2337-go-rewrite-m2-2-parse-month-references.md

@@ -0,0 +1,205 @@
+# Plan: Go rewrite — M2.2 `domain/czech.ParseMonthReferences`
+
+## Context
+
+M2.1 (`domain/czech.Normalize`) merged via PR #4 (`d9a61b3`) on
+2026-05-05. Per the [progress tracker](2026-05-03-2349-go-backend-rewrite-progress.md),
+**M2.2** is next: port `parse_month_references` from
+[scripts/czech_utils.py](../../scripts/czech_utils.py) to Go as
+`internal/domain/czech.ParseMonthReferences`.
+
+This function is the second-most-load-bearing pure helper after
+`reconcile`: every payment-message → month inference goes through it.
+Risk #4 in the [parent plan](2026-05-03-2349-go-backend-rewrite.md)
+specifically calls out its semantics — wrap-around year inference and
+the `m >= 10 → previous year` standalone heuristic — as easy to mis-port.
+
+This plan locks the test table against the live Python implementation
+*before* coding, so the Go port has a verified parity baseline even
+before the M3.1/M3.2 fixture infrastructure exists.
+
+## Scope
+
+- New file `go/internal/domain/czech/parse_month_references.go` in the
+  existing `czech` package (alongside [normalize.go](../../go/internal/domain/czech/normalize.go)).
+- New file `go/internal/domain/czech/parse_month_references_test.go`
+  with the test table below.
+- **Out of scope:** parity-fixture wiring (M3.1/M3.2); CLI hook-up
+  (M2.11/M2.12); any consumer call-sites.
+- **No new dependencies** — stdlib `regexp`, `sort`, `strconv`, `strings`
+  plus the existing `czech.Normalize` cover everything.
+
+## Recommended approach
+
+### Python contract to mirror
+
+Three regex passes, all run on `normalize(text)`:
+
+1. `([\d+]+)\s*/\s*(\d{2,4})` — captures `"11+12/2025"`, `"01/26"`, `"1/26"`.
+   Split the months part on `+`, keep digit-only tokens, validate `1..12`.
+   Year < 100 → year + 2000.
+2. `(\d{1,2})\s*\.\s*(\d{4})` — captures `"12.2025"`. **4-digit year only**
+   (so `"1.26"` does not match).
+3. Czech month names. First the **range** sub-pass:
+   `(name)\s*-\s*(name)` finds pairs; walk start→end with `m % 12 + 1`,
+   stopping when `m == end_m`. Wrap rule: if `start_m > end_m`, months
+   `>= start_m` are `defaultYear - 1`, the rest are `defaultYear`. Both
+   matched names go into a `foundInRanges` set.
+   Then the **standalone** sub-pass: `\b(name)\b`, skipping any name in
+   `foundInRanges`. For each remaining match, `m >= 10 → defaultYear - 1`,
+   else `defaultYear`.
+
+Output: sorted, deduplicated `[]string` of `"YYYY-MM"`.
+
+### Go signature
+
+```go
+package czech
+
+// ParseMonthReferences extracts YYYY-MM month references from Czech
+// free text. defaultYear seeds two heuristics: standalone month names
+// with m >= 10 are treated as defaultYear-1 (out-of-year backfill), and
+// wrap-around ranges (e.g. listopad-leden) place months >= start in
+// defaultYear-1.
+func ParseMonthReferences(text string, defaultYear int) []string
+```
+
+Required `defaultYear` (no default value — Go convention).
+
+### Implementation sketch
+
+```go
+var czechMonths = map[string]int{
+    "leden": 1, "ledna": 1, "lednu": 1,
+    "unor": 2, "unora": 2, "unoru": 2,
+    "brezen": 3, "brezna": 3, "breznu": 3,
+    "duben": 4, "dubna": 4, "dubnu": 4,
+    "kveten": 5, "kvetna": 5, "kvetnu": 5,
+    "cerven": 6, "cervna": 6, "cervnu": 6,
+    "cervenec": 7, "cervnce": 7, "cervenci": 7,
+    "srpen": 8, "srpna": 8, "srpnu": 8,
+    "zari": 9,
+    "rijen": 10, "rijna": 10, "rijnu": 10,
+    "listopad": 11, "listopadu": 11,
+    "prosinec": 12, "prosince": 12, "prosinci": 12,
+}
+
+// Sorted by descending length at init, so longer alternatives win in
+// the regex (e.g. "cervenec" beats "cerven"). Mirrors Python's
+// sorted(..., key=len, reverse=True).
+var monthNameAlt = buildMonthNameAlt()
+
+var (
+    numericRe = regexp.MustCompile(`([\d+]+)\s*/\s*(\d{2,4})`)
+    dotRe     = regexp.MustCompile(`(\d{1,2})\s*\.\s*(\d{4})`)
+    rangeRe   = regexp.MustCompile(`(` + monthNameAlt + `)\s*-\s*(` + monthNameAlt + `)`)
+    standRe   = regexp.MustCompile(`\b(` + monthNameAlt + `)\b`)
+)
+```
+
+Three Go-specific gotchas worth a code comment:
+
+1. **RE2 alternation is leftmost-first**, same as Python `re`. Sorting
+   month names by descending length is therefore necessary (otherwise
+   `"cervenec"` matches as `"cerven"` + leftover `"ec"`). Mirror the
+   Python sort exactly.
+2. **Map iteration is randomized in Go.** Build the alternation list
+   from a sorted slice of keys, not by iterating the map.
+3. **`\d` and `\b`** in Go RE2 are ASCII-only, which matches the
+   effective behavior on `Normalize`'d input (NFKD already collapsed
+   any Unicode digits/letters that would matter; standalone Devanagari
+   digits in member messages aren't a real-world concern).
+
+The walk loop uses a bounded counter (max 12 iterations) defensively in
+Go; Python's `while True` is fine because every range terminates within
+12 hops, but a future reader appreciates the bound.
+
+### Test table (verified against live Python — `default_year=2026`)
+
+Locked outputs from `PYTHONPATH=scripts:. python -c 'from czech_utils
+import parse_month_references; print(parse_month_references(<input>, 2026))'`
+on 2026-05-05.
+
+| # | Input | Expected | Path exercised |
+|---|---|---|---|
+| 1 | `""` | `[]` | empty |
+| 2 | `"11+12/2025"` | `["2025-11", "2025-12"]` | numeric, plus-split |
+| 3 | `"1/2026"` | `["2026-01"]` | numeric, single |
+| 4 | `"01/26"` | `["2026-01"]` | 2-digit year normalization |
+| 5 | `"11+12/25"` | `["2025-11", "2025-12"]` | plus-split + 2-digit year |
+| 6 | `"12+1+2/2026"` | `["2026-01", "2026-02", "2026-12"]` | sorting |
+| 7 | `"12.2025"` | `["2025-12"]` | dot pattern |
+| 8 | `"1.26"` | `[]` | dot pattern requires 4-digit year |
+| 9 | `"leden"` | `["2026-01"]` | standalone, m<10 |
+| 10 | `"prosinec"` | `["2025-12"]` | standalone, m≥10 → previous year |
+| 11 | `"prosince"` | `["2025-12"]` | declension |
+| 12 | `"lednu"` | `["2026-01"]` | declension |
+| 13 | `"rijen"` | `["2025-10"]` | m≥10 boundary (10 itself) |
+| 14 | `"zari"` | `["2026-09"]` | m<10 just below boundary |
+| 15 | `"listopad-leden"` | `["2025-11", "2025-12", "2026-01"]` | wrap range Nov→Jan |
+| 16 | `"rijen-leden"` | `["2025-10", "2025-11", "2025-12", "2026-01"]` | wrap from October |
+| 17 | `"unor-kveten"` | `["2026-02", "2026-03", "2026-04", "2026-05"]` | non-wrap range |
+| 18 | `"leden-leden"` | `["2026-01"]` | degenerate range |
+| 19 | `"unor-listopad"` | `["2026-02", ..., "2026-11"]` (10 entries) | range spans m≥10 — heuristic does NOT fire (range exclusion) |
+| 20 | `"cervenec-srpen"` | `["2026-07", "2026-08"]` | longest-match alt (`cervenec` not `cerven`+`ec`) |
+| 21 | `"listopad-leden, prosinec"` | `["2025-11", "2025-12", "2026-01"]` | range + standalone, dedup |
+| 22 | `"prosinec leden"` | `["2025-12", "2026-01"]` | two standalones, no range |
+| 23 | `"11+12/2025, leden-brezen"` | `["2025-11", "2025-12", "2026-01", "2026-02", "2026-03"]` | numeric + range mix |
+| 24 | `"11+12/25 a listopad"` | `["2025-11", "2025-12"]` | dedup across passes |
+| 25 | `"prosince/2025"` | `["2025-12"]` | numeric pattern fails (no digits before `/`); standalone fires |
+| 26 | `"listopad-prosinec/2025"` | `["2026-11", "2026-12"]` | range wins; numeric pattern fails |
+| 27 | `"01.2026 / 02.2026"` | `["2026-01", "2026-02"]` | dot pattern only; numeric matches `(2026, 02)` but month 2026 is out of range |
+| 28 | `"/12/2025"` | `["2025-12"]` | numeric matches at second `/` |
+| 29 | `"PROSINEC"` | `["2025-12"]` | normalize lowercases |
+| 30 | `"Žluťoučký prosinec"` | `["2025-12"]` | normalize strips diacritics |
+| 31 | `"Únor - květen"` | `["2026-02", ..., "2026-05"]` | range tolerates spaces around `-`, diacritics survive normalize |
+| 32 | `"platba 11/2025 a leden"` | `["2025-11", "2026-01"]` | mixed natural-language |
+| 33 | `"December"` | `[]` | English month names not recognized |
+| 34 | `"11+12/2025 11+12/2025"` | `["2025-11", "2025-12"]` | dedup of repeated input |
+| 35 | `"leden 2026"` | `["2026-01"]` | trailing year is ignored unless dot/slash separator present |
+
+35 cases is enough to lock semantics; the M3.x corpus will pile on
+real-message fixtures later.
+
+### Wire-up
+
+- No `go.mod` changes (stdlib only).
+- No CLI changes.
+- `Normalize` is in the same package, so call it directly.
+
+## Critical files
+
+- New: [go/internal/domain/czech/parse_month_references.go](../../go/internal/domain/czech/parse_month_references.go)
+- New: [go/internal/domain/czech/parse_month_references_test.go](../../go/internal/domain/czech/parse_month_references_test.go)
+- Reference (read-only): [scripts/czech_utils.py](../../scripts/czech_utils.py) — the porting source
+- Reference (read-only): [docs/plans/2026-05-03-2349-go-backend-rewrite.md](2026-05-03-2349-go-backend-rewrite.md) — risk #4
+- Reuses: [go/internal/domain/czech/normalize.go](../../go/internal/domain/czech/normalize.go) — `Normalize` is called once at the top of `ParseMonthReferences`
+
+## Verification
+
+End-to-end checks before marking M2.2 done:
+
+1. `cd go && go build ./...` — clean compile.
+2. `cd go && go test ./internal/domain/czech/...` — all 35 table cases green.
+3. `cd go && go test -race ./...` — race-clean (regex compiles are global; verify no init races).
+4. `cd go && golangci-lint run` (or `make go-lint` from repo root) — clean, gofumpt-formatted.
+5. **Spot parity** (manual, will be automated in M3.x): each test input has its expected output captured from the live Python implementation on 2026-05-05; the test table itself is the parity record. If any case diverges during implementation, re-run Python with the exact input to confirm the truth and update either the Go code or the test entry.
+6. `make go-build && make go-test && make go-lint` from repo root — proves M1/M2.1 gate still passes.
+
+## Branching & follow-up
+
+Per [CLAUDE.md](../../CLAUDE.md), this is feature work → branch + Gitea MR via `tea`:
+
+- Branch: `feat/m2-2-parse-month-references` off `main`.
+- Single focused commit, Co-Authored-By trailer.
+- Push with `-u`.
+- Open MR with `tea pr create --title "feat(go/M2.2): port czech.ParseMonthReferences" --description ... --base main --head feat/m2-2-parse-month-references`. Print the MR URL for the user.
+- User merges/deletes the branch in Gitea — never from the CLI.
+
+After merge (small doc edits land straight on `main` per CLAUDE.md exception):
+
+- Tick `M2.2` in the [progress tracker](2026-05-03-2349-go-backend-rewrite-progress.md) with the merge SHA.
+- Add a one-line `CHANGELOG.md` entry (timestamp via `date "+%Y-%m-%d %H:%M %Z"`).
+- Record any porting surprise (e.g. an unexpected diff between Go RE2 and Python `re`) in the tracker's "Notes & decisions" section.
+
+Next task is **M2.3 `domain/fees.CalculateFee`** — straightforward constants table; no parser semantics to debate.

docs/plans/2026-05-06-0928-go-m2-5-money-parse-czk.md

@@ -0,0 +1,199 @@
+# M2.5 — Port `parse_czk_amount` to `domain/money.ParseCZK`
+
+> On execution, this plan should be moved to
+> `docs/plans/2026-05-06-0928-go-m2-5-money-parse-czk.md` per project CLAUDE.md
+> (`docs/plans/YYYY-MM-DD-HHMM-<slug>.md`). Plan mode forces it to live under
+> `~/.claude/plans/` until then.
+
+## 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–M2.4 are landed. Next leaf-level pure function is
+`parse_czk_amount` from [scripts/infer_payments.py:17-45](../../srv/personal/fuj-management/scripts/infer_payments.py#L17-L45),
+the Czech-locale amount parser used at [scripts/infer_payments.py:124](../../srv/personal/fuj-management/scripts/infer_payments.py#L124)
+when reading the `Inferred Amount` column out of the payments sheet.
+
+It's a small, isolated string→float helper, but its heuristic for
+disambiguating `.` and `,` as decimal vs thousand separator is
+non-obvious and needs to behave identically in Go to keep parity once
+the Go infer pipeline lands in M4.8.
+
+## Python behaviour (the spec)
+
+```py
+def parse_czk_amount(val) -> float:
+    if val is None or val == "":
+        return 0.0
+    if isinstance(val, (int, float)):
+        return float(val)
+
+    val = str(val)
+    val = val.replace("Kč", "").replace("CZK", "").strip()
+    if "," in val:
+        # 1.500,00 -> 1500.00 — comma is decimal sep
+        val = val.replace(".", "").replace(" ", "").replace(",", ".")
+    else:
+        if val.count(".") > 1:
+            # 1.500.000 -> 1500000 — multiple dots = thousand sep
+            val = val.replace(".", "").replace(" ", "")
+        else:
+            # "1 500.00" -> "1500.00", "1.500" stays "1.500" (= 1.5)
+            val = val.replace(" ", "")
+    try:
+        return float(val)
+    except ValueError:
+        return 0.0
+```
+
+Key behavioural notes for the Go port:
+
+1. Empty / None → 0, no error.
+2. `"1.500"` (single dot, no comma) is parsed as **1.5**, not 1500.
+   The heuristic intentionally treats a lone dot as decimal.
+3. `"1.500,00"` → 1500.0 (comma wins, dots are thousand seps).
+4. `"1.500.000"` → 1500000.0 (multiple dots → all thousand seps).
+5. `"1 500"` / `"1 500.00"` / `"500 Kč"` → spaces stripped.
+6. Garbage → 0, no error in Python.
+7. Strips literal substrings `"Kč"` and `"CZK"` (case-sensitive in Python).
+
+## Approach
+
+Create new package `internal/domain/money` mirroring the layout of
+`internal/domain/fees` (single-file module + test file alongside).
+
+### Signature
+
+```go
+// Package money ports Czech-locale currency parsing from
+// scripts/infer_payments.py.
+package money
+
+// ParseCZK parses a Czech-locale amount string and returns the value
+// in CZK as a float64.
+//
+// Mirrors scripts/infer_payments.py parse_czk_amount:
+//   - empty input → (0, nil)
+//   - "Kč"/"CZK" suffixes are stripped (case-sensitive, like Python)
+//   - if input contains ",", comma is the decimal separator and
+//     dots/spaces are thousand separators ("1.500,00" → 1500.0)
+//   - else if input contains 2+ dots, all dots are thousand seps
+//     ("1.500.000" → 1500000.0)
+//   - else single dot stays as the decimal point ("1.500" → 1.5,
+//     matching the Python heuristic)
+//   - on parse failure, returns (0, ErrInvalidAmount). Callers wanting
+//     Python-equivalent silent-zero behaviour can discard the error.
+func ParseCZK(s string) (float64, error)
+```
+
+`ErrInvalidAmount` is a package-level sentinel:
+
+```go
+var ErrInvalidAmount = errors.New("money: invalid CZK amount")
+```
+
+Why `(float64, error)` instead of mirroring Python's silent zero:
+
+- Go idiom prefers explicit errors.
+- The single Python call site doesn't distinguish parse-fail from
+  empty-input (both → 0), so if we want byte-equal behaviour at the
+  Go infer site (M4.8), the caller can `v, _ := money.ParseCZK(s)`
+  and get exactly the Python result.
+- Future callers (e.g. user-facing import flows) may want to surface
+  the error.
+
+This matches the precedent set in M2.4 where we used
+`Expected{Unknown bool}` rather than copying the Python `"?"` sentinel
+verbatim — Go-idiomatic surface, parity-preserving semantics.
+
+### Polymorphic input?
+
+Python's `parse_czk_amount` also accepts raw int/float (passed through
+unchanged) because Google Sheets API can return numeric cells as
+`float64` rather than strings. **Skip this in Go.** The Sheets IO
+adapter is M4.2, and that's where the `[]any` → string normalisation
+will live. Keeping `ParseCZK` string-only keeps the leaf function tiny.
+
+### Tests
+
+`money_test.go` mirrors the existing `fees_test.go` table-driven style,
+including the verification comment showing the Python command used to
+confirm each expected value:
+
+```sh
+PYTHONPATH=scripts:. python -c '
+from infer_payments import parse_czk_amount
+for v in [None, "", "0", "500", "500 Kč", "500 CZK",
+          "1 500", "1500.00", "1 500.00",
+          "1.500,00", "1500,5", "1.500.000",
+          "1.500", "abc", "  ", "100,5 Kč"]:
+    print(repr(v), "->", parse_czk_amount(v))
+'
+```
+
+Cases to cover (all numeric outputs verified against the Python output
+of the snippet above):
+
+| input | expected |
+|---|---|
+| `""` | 0 |
+| `"0"` | 0 |
+| `"500"` | 500 |
+| `"500 Kč"` | 500 |
+| `"500 CZK"` | 500 |
+| `"1 500"` | 1500 |
+| `"1500.00"` | 1500 |
+| `"1 500.00"` | 1500 |
+| `"1.500,00"` | 1500 |
+| `"1500,5"` | 1500.5 |
+| `"1.500.000"` | 1500000 |
+| `"1.500"` | 1.5 *(heuristic — single dot = decimal)* |
+| `"100,5 Kč"` | 100.5 |
+| `"abc"` | 0, returns `ErrInvalidAmount` |
+| `"  "` | 0, returns `ErrInvalidAmount` *(or 0 nil — confirm against Python; trim leaves `""`, then `float("")` raises → Python returns 0; Go test will assert whichever Python actually produces)* |
+
+The `"  "` row is the only one that needs the Python verification step
+to settle — once verified, lock the behaviour in.
+
+Also add a "documentation example" assertion in the test that
+`v, _ := ParseCZK(s)` recovers the Python silent-zero contract for
+every garbage input, so we don't lose that property at the Go infer
+call site.
+
+## Files to create
+
+- `go/internal/domain/money/money.go` — package + `ParseCZK` + `ErrInvalidAmount`
+- `go/internal/domain/money/money_test.go` — table-driven tests
+
+No existing Go files need editing.
+
+## Verification
+
+```sh
+cd go && go test ./internal/domain/money/...
+make go-lint
+make go-build   # sanity: nothing else broke
+```
+
+Also run the Python snippet from the Tests section above and diff its
+output against the test table to confirm parity.
+
+## Out of scope (explicit non-goals)
+
+- Polymorphic `any` input — leave for M4.2 IO adapter.
+- Hooking into the Tier-1 parity runner — that comes with M3.5
+  (`-tags=parity` build constraint). M2.5 just needs unit tests.
+- Any callsite migration — `infer_payments.py` keeps using its own
+  Python function until M4.8.
+
+## Progress tracker + changelog
+
+After the commit lands:
+
+- Tick `M2.5` 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 M2.4 entry style.
+- Add a CHANGELOG.md entry at top:
+  `## YYYY-MM-DD HH:MM TZ — feat(go/M2.5): port domain/money.ParseCZK`.
+
+Branch: `feat/m2-5-money-parse-czk` (per CLAUDE.md branch-per-feature
+workflow). Push, open MR via `tea pr create`, leave merge to the user.

go/internal/domain/czech/parse_month_references.go

@@ -0,0 +1,154 @@
+package czech
+
+import (
+	"fmt"
+	"regexp"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+var czechMonths = map[string]int{
+	"leden": 1, "ledna": 1, "lednu": 1,
+	"unor": 2, "unora": 2, "unoru": 2,
+	"brezen": 3, "brezna": 3, "breznu": 3,
+	"duben": 4, "dubna": 4, "dubnu": 4,
+	"kveten": 5, "kvetna": 5, "kvetnu": 5,
+	"cerven": 6, "cervna": 6, "cervnu": 6,
+	"cervenec": 7, "cervnce": 7, "cervenci": 7,
+	"srpen": 8, "srpna": 8, "srpnu": 8,
+	"zari":  9,
+	"rijen": 10, "rijna": 10, "rijnu": 10,
+	"listopad": 11, "listopadu": 11,
+	"prosinec": 12, "prosince": 12, "prosinci": 12,
+}
+
+var (
+	numericRe *regexp.Regexp
+	dotRe     *regexp.Regexp
+	rangeRe   *regexp.Regexp
+	standRe   *regexp.Regexp
+)
+
+func init() {
+	// Sort by descending length so longer alternatives win in RE2 leftmost-first
+	// matching (e.g. "cervenec" is tried before "cerven").
+	names := make([]string, 0, len(czechMonths))
+	for name := range czechMonths {
+		names = append(names, name)
+	}
+	sort.Slice(names, func(i, j int) bool {
+		if len(names[i]) != len(names[j]) {
+			return len(names[i]) > len(names[j])
+		}
+		return names[i] < names[j]
+	})
+	alt := strings.Join(names, "|")
+
+	numericRe = regexp.MustCompile(`([\d+]+)\s*/\s*(\d{2,4})`)
+	dotRe = regexp.MustCompile(`(\d{1,2})\s*\.\s*(\d{4})`)
+	rangeRe = regexp.MustCompile(`(` + alt + `)\s*-\s*(` + alt + `)`)
+	standRe = regexp.MustCompile(`\b(` + alt + `)\b`)
+}
+
+// ParseMonthReferences extracts YYYY-MM month references from Czech free text.
+//
+// defaultYear seeds two heuristics: standalone month names with m >= 10 are
+// treated as defaultYear-1 (out-of-year backfill), and wrap-around ranges
+// (e.g. listopad-leden) place months >= start_m in defaultYear-1.
+//
+// Returns a sorted, deduplicated slice of "YYYY-MM" strings.
+func ParseMonthReferences(text string, defaultYear int) []string {
+	normalized := Normalize(text)
+	seen := map[string]struct{}{}
+
+	add := func(year, m int) {
+		if m >= 1 && m <= 12 {
+			seen[fmt.Sprintf("%04d-%02d", year, m)] = struct{}{}
+		}
+	}
+
+	// Pass 1: numeric months — "11+12/2025", "01/26", "1/2026"
+	for _, groups := range numericRe.FindAllStringSubmatch(normalized, -1) {
+		monthsPart, yearStr := groups[1], groups[2]
+		year, err := strconv.Atoi(yearStr)
+		if err != nil {
+			continue
+		}
+		if year < 100 {
+			year += 2000
+		}
+		for mStr := range strings.SplitSeq(monthsPart, "+") {
+			mStr = strings.TrimSpace(mStr)
+			if mStr == "" {
+				continue
+			}
+			allDigits := true
+			for _, c := range mStr {
+				if c < '0' || c > '9' {
+					allDigits = false
+					break
+				}
+			}
+			if !allDigits {
+				continue
+			}
+			m, err := strconv.Atoi(mStr)
+			if err != nil {
+				continue
+			}
+			add(year, m)
+		}
+	}
+
+	// Pass 2: dot-separated month.year — "12.2025" (4-digit year only)
+	for _, groups := range dotRe.FindAllStringSubmatch(normalized, -1) {
+		m, _ := strconv.Atoi(groups[1])
+		year, _ := strconv.Atoi(groups[2])
+		add(year, m)
+	}
+
+	// Pass 3a: Czech month name ranges — "listopad-leden"
+	foundInRanges := map[string]struct{}{}
+	for _, groups := range rangeRe.FindAllStringSubmatch(normalized, -1) {
+		startName, endName := groups[1], groups[2]
+		foundInRanges[startName] = struct{}{}
+		foundInRanges[endName] = struct{}{}
+		startM := czechMonths[startName]
+		endM := czechMonths[endName]
+		wraps := startM > endM
+		m := startM
+		for range 12 {
+			year := defaultYear
+			if wraps && m >= startM {
+				year = defaultYear - 1
+			}
+			add(year, m)
+			if m == endM {
+				break
+			}
+			m = m%12 + 1
+		}
+	}
+
+	// Pass 3b: standalone Czech month names (not part of a range)
+	for _, groups := range standRe.FindAllStringSubmatch(normalized, -1) {
+		name := groups[1]
+		if _, inRange := foundInRanges[name]; inRange {
+			continue
+		}
+		m := czechMonths[name]
+		year := defaultYear
+		if m >= 10 {
+			year = defaultYear - 1
+		}
+		add(year, m)
+	}
+
+	result := make([]string, 0, len(seen))
+	for k := range seen {
+		result = append(result, k)
+	}
+	sort.Strings(result)
+	return result
+}

go/internal/domain/czech/parse_month_references_test.go

@@ -0,0 +1,244 @@
+package czech
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestParseMonthReferences(t *testing.T) {
+	t.Parallel()
+
+	// All expected outputs verified against live Python implementation on 2026-05-05:
+	//   PYTHONPATH=scripts:. python -c 'from czech_utils import parse_month_references; print(parse_month_references("<input>", 2026))'
+	tests := []struct {
+		name        string
+		input       string
+		defaultYear int
+		want        []string
+	}{
+		{
+			name:        "empty",
+			input:       "",
+			defaultYear: 2026,
+			want:        []string{},
+		},
+		{
+			name:        "numeric plus-split two months full year",
+			input:       "11+12/2025",
+			defaultYear: 2026,
+			want:        []string{"2025-11", "2025-12"},
+		},
+		{
+			name:        "numeric single month full year",
+			input:       "1/2026",
+			defaultYear: 2026,
+			want:        []string{"2026-01"},
+		},
+		{
+			name:        "numeric 2-digit year",
+			input:       "01/26",
+			defaultYear: 2026,
+			want:        []string{"2026-01"},
+		},
+		{
+			name:        "numeric plus-split with 2-digit year",
+			input:       "11+12/25",
+			defaultYear: 2026,
+			want:        []string{"2025-11", "2025-12"},
+		},
+		{
+			name:        "numeric three months sorted",
+			input:       "12+1+2/2026",
+			defaultYear: 2026,
+			want:        []string{"2026-01", "2026-02", "2026-12"},
+		},
+		{
+			name:        "dot pattern",
+			input:       "12.2025",
+			defaultYear: 2026,
+			want:        []string{"2025-12"},
+		},
+		{
+			name:        "dot pattern requires 4-digit year",
+			input:       "1.26",
+			defaultYear: 2026,
+			want:        []string{},
+		},
+		{
+			name:        "standalone month below m10 threshold",
+			input:       "leden",
+			defaultYear: 2026,
+			want:        []string{"2026-01"},
+		},
+		{
+			name:        "standalone month m10 heuristic",
+			input:       "prosinec",
+			defaultYear: 2026,
+			want:        []string{"2025-12"},
+		},
+		{
+			name:        "declension prosince",
+			input:       "prosince",
+			defaultYear: 2026,
+			want:        []string{"2025-12"},
+		},
+		{
+			name:        "declension lednu",
+			input:       "lednu",
+			defaultYear: 2026,
+			want:        []string{"2026-01"},
+		},
+		{
+			name:        "standalone m10 boundary (rijen = October)",
+			input:       "rijen",
+			defaultYear: 2026,
+			want:        []string{"2025-10"},
+		},
+		{
+			name:        "standalone m9 just below boundary (zari = September)",
+			input:       "zari",
+			defaultYear: 2026,
+			want:        []string{"2026-09"},
+		},
+		{
+			name:        "range wrap Nov-Jan",
+			input:       "listopad-leden",
+			defaultYear: 2026,
+			want:        []string{"2025-11", "2025-12", "2026-01"},
+		},
+		{
+			name:        "range wrap starting at October",
+			input:       "rijen-leden",
+			defaultYear: 2026,
+			want:        []string{"2025-10", "2025-11", "2025-12", "2026-01"},
+		},
+		{
+			name:        "range no wrap",
+			input:       "unor-kveten",
+			defaultYear: 2026,
+			want:        []string{"2026-02", "2026-03", "2026-04", "2026-05"},
+		},
+		{
+			name:        "degenerate range same month",
+			input:       "leden-leden",
+			defaultYear: 2026,
+			want:        []string{"2026-01"},
+		},
+		{
+			name:        "range spanning m10 — heuristic does NOT fire for range members",
+			input:       "unor-listopad",
+			defaultYear: 2026,
+			want:        []string{"2026-02", "2026-03", "2026-04", "2026-05", "2026-06", "2026-07", "2026-08", "2026-09", "2026-10", "2026-11"},
+		},
+		{
+			name:        "longest-match alternation cervenec beats cerven",
+			input:       "cervenec-srpen",
+			defaultYear: 2026,
+			want:        []string{"2026-07", "2026-08"},
+		},
+		{
+			name:        "range plus standalone — range excludes, dedup",
+			input:       "listopad-leden, prosinec",
+			defaultYear: 2026,
+			want:        []string{"2025-11", "2025-12", "2026-01"},
+		},
+		{
+			name:        "two standalones no range",
+			input:       "prosinec leden",
+			defaultYear: 2026,
+			want:        []string{"2025-12", "2026-01"},
+		},
+		{
+			name:        "numeric plus range mix",
+			input:       "11+12/2025, leden-brezen",
+			defaultYear: 2026,
+			want:        []string{"2025-11", "2025-12", "2026-01", "2026-02", "2026-03"},
+		},
+		{
+			name:        "dedup across numeric and standalone passes",
+			input:       "11+12/25 a listopad",
+			defaultYear: 2026,
+			want:        []string{"2025-11", "2025-12"},
+		},
+		{
+			name:        "no digits before slash — standalone fires instead",
+			input:       "prosince/2025",
+			defaultYear: 2026,
+			want:        []string{"2025-12"},
+		},
+		{
+			name:        "range with trailing slash-year — numeric fails, range wins",
+			input:       "listopad-prosinec/2025",
+			defaultYear: 2026,
+			want:        []string{"2026-11", "2026-12"},
+		},
+		{
+			name:        "dot pattern only — numeric matches but month out of 1-12 range",
+			input:       "01.2026 / 02.2026",
+			defaultYear: 2026,
+			want:        []string{"2026-01", "2026-02"},
+		},
+		{
+			name:        "leading slash — numeric matches at second slash",
+			input:       "/12/2025",
+			defaultYear: 2026,
+			want:        []string{"2025-12"},
+		},
+		{
+			name:        "uppercase input normalized",
+			input:       "PROSINEC",
+			defaultYear: 2026,
+			want:        []string{"2025-12"},
+		},
+		{
+			name:        "diacritics stripped by Normalize",
+			input:       "Žluťoučký prosinec",
+			defaultYear: 2026,
+			want:        []string{"2025-12"},
+		},
+		{
+			name:        "diacritics in range with spaces around dash",
+			input:       "Únor - květen",
+			defaultYear: 2026,
+			want:        []string{"2026-02", "2026-03", "2026-04", "2026-05"},
+		},
+		{
+			name:        "natural language mixed with numeric and standalone",
+			input:       "platba 11/2025 a leden",
+			defaultYear: 2026,
+			want:        []string{"2025-11", "2026-01"},
+		},
+		{
+			name:        "English month name not recognized",
+			input:       "December",
+			defaultYear: 2026,
+			want:        []string{},
+		},
+		{
+			name:        "duplicate input deduped",
+			input:       "11+12/2025 11+12/2025",
+			defaultYear: 2026,
+			want:        []string{"2025-11", "2025-12"},
+		},
+		{
+			name:        "trailing year without separator ignored",
+			input:       "leden 2026",
+			defaultYear: 2026,
+			want:        []string{"2026-01"},
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := ParseMonthReferences(tc.input, tc.defaultYear)
+			if got == nil {
+				got = []string{}
+			}
+			if !reflect.DeepEqual(got, tc.want) {
+				t.Errorf("ParseMonthReferences(%q, %d)\n  got  %v\n  want %v",
+					tc.input, tc.defaultYear, got, tc.want)
+			}
+		})
+	}
+}

go/internal/domain/fees/fees.go

@@ -0,0 +1,34 @@
+// Package fees ports fee calculation from scripts/attendance.py.
+package fees
+
+const (
+	AdultFeeDefault = 700 // CZK fallback for 2+ practices when month not in AdultFeeMonthlyRate
+	AdultFeeSingle  = 200 // CZK for exactly 1 practice
+)
+
+// AdultFeeMonthlyRate mirrors ADULT_FEE_MONTHLY_RATE in scripts/attendance.py.
+// Months absent from this map fall back to AdultFeeDefault.
+var AdultFeeMonthlyRate = map[string]int{
+	"2025-09": 750, "2025-10": 750, "2025-11": 750, "2025-12": 750,
+	"2026-01": 750, "2026-02": 750, "2026-03": 350,
+	"2026-04": 700, "2026-05": 700,
+}
+
+// CalculateFee returns the adult fee in CZK for attendanceCount practices in
+// the given monthKey (format "YYYY-MM").
+//
+//	0 practices → 0
+//	1 practice  → AdultFeeSingle (200)
+//	2+          → AdultFeeMonthlyRate[monthKey] or AdultFeeDefault
+func CalculateFee(attendanceCount int, monthKey string) int {
+	if attendanceCount == 0 {
+		return 0
+	}
+	if attendanceCount == 1 {
+		return AdultFeeSingle
+	}
+	if rate, ok := AdultFeeMonthlyRate[monthKey]; ok {
+		return rate
+	}
+	return AdultFeeDefault
+}

go/internal/domain/fees/fees_test.go

@@ -0,0 +1,37 @@
+package fees
+
+import "testing"
+
+func TestCalculateFee(t *testing.T) {
+	t.Parallel()
+
+	// All expected outputs verified against live Python implementation on 2026-05-06:
+	//   PYTHONPATH=scripts:. python -c 'from attendance import calculate_fee; print([calculate_fee(c,m) for c,m in [(0,"2026-05"),(0,""),(1,"2026-05"),(1,"unknown"),(2,"2026-05"),(2,"2026-03"),(2,"2025-09"),(5,"2026-05"),(2,"2027-01"),(2,"")]])'
+	tests := []struct {
+		name  string
+		count int
+		month string
+		want  int
+	}{
+		{"zero short-circuits", 0, "2026-05", 0},
+		{"zero empty month", 0, "", 0},
+		{"single practice", 1, "2026-05", 200},
+		{"single ignores monthKey", 1, "unknown", 200},
+		{"two practices configured month", 2, "2026-05", 700},
+		{"two practices reduced march", 2, "2026-03", 350},
+		{"two practices early season", 2, "2025-09", 750},
+		{"high count same as two", 5, "2026-05", 700},
+		{"unknown future month falls back", 2, "2027-01", 700},
+		{"empty month falls back", 2, "", 700},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := CalculateFee(tc.count, tc.month)
+			if got != tc.want {
+				t.Errorf("CalculateFee(%d, %q) = %d, want %d", tc.count, tc.month, got, tc.want)
+			}
+		})
+	}
+}

go/internal/domain/fees/junior.go

@@ -0,0 +1,37 @@
+package fees
+
+const JuniorFeeDefault = 500 // CZK fallback for 2+ practices when month not in JuniorFeeMonthlyRate
+
+// JuniorFeeMonthlyRate mirrors JUNIOR_MONTHLY_RATE in scripts/attendance.py.
+// Months absent from this map fall back to JuniorFeeDefault.
+var JuniorFeeMonthlyRate = map[string]int{
+	"2025-09": 250,
+	"2026-03": 250,
+}
+
+// Expected is the result of a junior fee calculation.
+// When Unknown is true the fee requires manual review (Python returns "?");
+// in that case Value is meaningless — always check Unknown first.
+type Expected struct {
+	Value   int
+	Unknown bool
+}
+
+// CalculateJuniorFee returns the junior fee for attendanceCount practices in
+// the given monthKey (format "YYYY-MM").
+//
+//	0 practices → Expected{Value: 0}
+//	1 practice  → Expected{Unknown: true}  (manual review; Python sentinel "?")
+//	2+          → Expected{Value: JuniorFeeMonthlyRate[monthKey] or JuniorFeeDefault}
+func CalculateJuniorFee(attendanceCount int, monthKey string) Expected {
+	if attendanceCount == 0 {
+		return Expected{Value: 0}
+	}
+	if attendanceCount == 1 {
+		return Expected{Unknown: true}
+	}
+	if rate, ok := JuniorFeeMonthlyRate[monthKey]; ok {
+		return Expected{Value: rate}
+	}
+	return Expected{Value: JuniorFeeDefault}
+}

go/internal/domain/fees/junior_test.go

@@ -0,0 +1,37 @@
+package fees
+
+import "testing"
+
+func TestCalculateJuniorFee(t *testing.T) {
+	t.Parallel()
+
+	// All expected outputs verified against live Python implementation on 2026-05-06:
+	//   PYTHONPATH=scripts:. python -c 'from attendance import calculate_junior_fee; print([calculate_junior_fee(c,m) for c,m in [(0,"2026-05"),(0,""),(1,"2026-05"),(1,"unknown"),(2,"2026-05"),(2,"2025-09"),(2,"2026-03"),(5,"2025-09"),(2,"2027-01"),(2,"")]])'
+	tests := []struct {
+		name  string
+		count int
+		month string
+		want  Expected
+	}{
+		{"zero short-circuits", 0, "2026-05", Expected{Value: 0}},
+		{"zero empty month", 0, "", Expected{Value: 0}},
+		{"single practice sentinel", 1, "2026-05", Expected{Unknown: true}},
+		{"single ignores monthKey", 1, "unknown", Expected{Unknown: true}},
+		{"two practices default month", 2, "2026-05", Expected{Value: 500}},
+		{"two practices reduced sept", 2, "2025-09", Expected{Value: 250}},
+		{"two practices reduced march", 2, "2026-03", Expected{Value: 250}},
+		{"high count same as two", 5, "2025-09", Expected{Value: 250}},
+		{"unknown future month falls back", 2, "2027-01", Expected{Value: 500}},
+		{"empty month falls back", 2, "", Expected{Value: 500}},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got := CalculateJuniorFee(tc.count, tc.month)
+			if got != tc.want {
+				t.Errorf("CalculateJuniorFee(%d, %q) = %+v, want %+v", tc.count, tc.month, got, tc.want)
+			}
+		})
+	}
+}

go/internal/domain/money/money.go

@@ -0,0 +1,49 @@
+// Package money ports Czech-locale currency parsing from scripts/infer_payments.py.
+package money
+
+import (
+	"errors"
+	"strconv"
+	"strings"
+)
+
+// ErrInvalidAmount is returned by ParseCZK when the input cannot be parsed.
+var ErrInvalidAmount = errors.New("money: invalid CZK amount")
+
+// ParseCZK parses a Czech-locale amount string and returns the value in CZK
+// as a float64. Mirrors scripts/infer_payments.py parse_czk_amount:
+//
+//   - empty input → (0, nil)
+//   - "Kč"/"CZK" suffixes stripped (case-sensitive, like Python)
+//   - comma present → comma is decimal sep, dots/spaces are thousand seps
+//     ("1.500,00" → 1500.0)
+//   - no comma, 2+ dots → all dots are thousand seps ("1.500.000" → 1500000.0)
+//   - no comma, ≤1 dot → dot is decimal sep ("1.500" → 1.5)
+//   - on parse failure → (0, ErrInvalidAmount); callers wanting Python's
+//     silent-zero behaviour can discard the error: v, _ := ParseCZK(s)
+func ParseCZK(s string) (float64, error) {
+	if s == "" {
+		return 0, nil
+	}
+
+	s = strings.ReplaceAll(s, "Kč", "")
+	s = strings.ReplaceAll(s, "CZK", "")
+	s = strings.TrimSpace(s)
+
+	if strings.ContainsRune(s, ',') {
+		s = strings.ReplaceAll(s, ".", "")
+		s = strings.ReplaceAll(s, " ", "")
+		s = strings.ReplaceAll(s, ",", ".")
+	} else if strings.Count(s, ".") > 1 {
+		s = strings.ReplaceAll(s, ".", "")
+		s = strings.ReplaceAll(s, " ", "")
+	} else {
+		s = strings.ReplaceAll(s, " ", "")
+	}
+
+	v, err := strconv.ParseFloat(s, 64)
+	if err != nil {
+		return 0, ErrInvalidAmount
+	}
+	return v, nil
+}

go/internal/domain/money/money_test.go

@@ -0,0 +1,67 @@
+package money
+
+import (
+	"testing"
+)
+
+func TestParseCZK(t *testing.T) {
+	t.Parallel()
+
+	// All expected outputs verified against live Python implementation on 2026-05-06:
+	//   PYTHONPATH=scripts:. python -c '
+	//   from infer_payments import parse_czk_amount
+	//   for v in [None, "", "0", "500", "500 Kč", "500 CZK",
+	//             "1 500", "1500.00", "1 500.00",
+	//             "1.500,00", "1500,5", "1.500.000",
+	//             "1.500", "abc", "  ", "100,5 Kč"]:
+	//       print(repr(v), "->", parse_czk_amount(v))
+	//   '
+	tests := []struct {
+		name    string
+		input   string
+		want    float64
+		wantErr bool
+	}{
+		{"empty string", "", 0, false},
+		{"zero string", "0", 0, false},
+		{"plain integer", "500", 500, false},
+		{"with Kč suffix", "500 Kč", 500, false},
+		{"with CZK suffix", "500 CZK", 500, false},
+		{"space thousand sep", "1 500", 1500, false},
+		{"dot decimal", "1500.00", 1500, false},
+		{"space thousands dot decimal", "1 500.00", 1500, false},
+		{"dot thousand comma decimal", "1.500,00", 1500, false},
+		{"comma decimal no thousands", "1500,5", 1500.5, false},
+		{"multiple dot thousand seps", "1.500.000", 1500000, false},
+		{"single dot is decimal heuristic", "1.500", 1.5, false},
+		{"comma decimal with Kč", "100,5 Kč", 100.5, false},
+		{"garbage text", "abc", 0, true},
+		{"spaces only", "  ", 0, true},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got, err := ParseCZK(tc.input)
+			if (err != nil) != tc.wantErr {
+				t.Errorf("ParseCZK(%q) error = %v, wantErr %v", tc.input, err, tc.wantErr)
+			}
+			if got != tc.want {
+				t.Errorf("ParseCZK(%q) = %v, want %v", tc.input, got, tc.want)
+			}
+		})
+	}
+}
+
+// TestParseCZKSilentZero documents that discarding the error recovers Python's
+// silent-zero behaviour for any garbage input.
+func TestParseCZKSilentZero(t *testing.T) {
+	t.Parallel()
+
+	for _, s := range []string{"abc", "  ", "Kč", "CZK"} {
+		v, _ := ParseCZK(s)
+		if v != 0 {
+			t.Errorf("ParseCZK(%q) silent-zero: got %v, want 0", s, v)
+		}
+	}
+}