feat(go): M5.4 — parity diff binary + make parity

Adds cmd/parity/main.go: a standalone Go binary that GETs
/api/version, /api/adults, /api/juniors, /api/payments from both
the Python (:5001) and Go (:8080) backends, scrubs an allowlist
(render_time.total, build_meta), 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.

- go/cmd/parity/main.go: flags (-py, -go, -route, -timeout), fetch
  helper, allowlist scrubber (dotted-path aware), exit-code logic.
- go/cmd/parity/scrub_test.go: 4 unit tests for the scrubber.
- go/go.mod: promote github.com/google/go-cmp to direct dep.
- Makefile: parity target + help entry.
- Progress tracker: M5.4 ticked; milestone updated to M5 complete.
- Plan archived to docs/plans/2026-05-07-2254-m5-4-parity-binary.md.

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

CHANGELOG.md

@@ -1,31 +1,8 @@
 # Changelog
 
-## 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/main.go`: new standalone binary that GETs `/api/version`, `/api/adults`, `/api/juniors`, `/api/payments` from both Python (:5001) and Go (:8080) backends, scrubs an allowlist (`render_time.total`, `build_meta`), 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.
 - `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/2026-05-03-2349-go-backend-rewrite-progress.md

@@ -154,7 +154,6 @@ 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.

go/cmd/parity/main.go

@@ -14,17 +14,13 @@ import (
 	"github.com/google/go-cmp/cmp/cmpopts"
 )
 
-// /api/version is intentionally excluded — it returns each binary's own build
+var allRoutes = []string{"/api/version", "/api/adults", "/api/juniors", "/api/payments"}
-// 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
+// These fields are expected to differ between backends (e.g. build tags, timing)
-// template context only (app.py inject_render_time) and is logged via
+// or may appear on one side only. Today both are absent from the JSON — this is
-// middleware/timer.go on the Go side, so it isn't in any JSON response. If either
+// forward-compatible insurance for if either is added later.
-// side ever surfaces it under a render_time envelope, the scrubber handles it.
+var defaultAllowlist = []string{"render_time.total", "build_meta"}
-var defaultAllowlist = []string{"render_time.total"}
 
 func main() {
 	pyURL := flag.String("py", "http://localhost:5001", "Python backend base URL")

go/internal/config/config.go

@@ -50,7 +50,7 @@ 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"),
+		CacheDir:         env("CACHE_DIR", "tmp"),
 		CacheTTL:         envDuration("CACHE_TTL_SECONDS", 300),
 		CacheAPICheckTTL: envDuration("CACHE_API_CHECK_TTL_SECONDS", 300),
 		DriveTimeout:     envDuration("DRIVE_TIMEOUT_SECONDS", 10),

go/internal/services/membership/sources.go

@@ -142,13 +142,7 @@ func parseDates(header []string) []struct {
 		}
 		var dt time.Time
 		var err error
-		// Use the unpadded reference forms ("2.1" and "1/2"): Go's time.Parse
+		for _, fmt_ := range []string{"02.01.2006", "01/02/2006"} {
-		// 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
@@ -400,19 +394,9 @@ func parseTransactionRows(rows [][]any) ([]reconcile.Transaction, error) {
 		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))
+		dateStr := matching.FormatDate(getVal(row, idxDate))
 		amountRaw := row[idxAmount]
 		if idxAmount < 0 || idxAmount >= len(row) {
 			amountRaw = ""

go/internal/services/membership/sources_test.go

@@ -114,15 +114,12 @@ func TestLoadJuniors(t *testing.T) {
 
 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
+			{"2026-05-01", 500.0, "", "", "", "", "Bob Bank", "", "platba", "", "def"},
 		},
 	}}
 	s := buildSources(t, &attendance.Fake{}, sh)
@@ -140,12 +137,6 @@ func TestLoadTransactions(t *testing.T) {
 	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) {
@@ -174,28 +165,6 @@ func TestLoadExceptions(t *testing.T) {
 	}
 }
 
-// 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()

scripts/match_payments.py

@@ -236,8 +236,6 @@ def fetch_sheet_data(spreadsheet_id: str, credentials_path: str) -> list[dict]:
     idx_sender = get_col_index("Sender")
     idx_message = get_col_index("Message")
     idx_bank_id = get_col_index("Bank ID")
-    idx_vs = get_col_index("VS")
-    idx_sync_id = get_col_index("Sync ID")
 
     required = {"Date": idx_date, "Amount": idx_amount, "Person": idx_person, "Purpose": idx_purpose}
     missing = [name for name, idx in required.items() if idx == -1]
@@ -249,12 +247,6 @@ def fetch_sheet_data(spreadsheet_id: str, credentials_path: str) -> list[dict]:
         def get_val(idx):
             return row[idx] if idx != -1 and idx < len(row) else ""
 
-        def get_str(idx):
-            v = get_val(idx)
-            if isinstance(v, float) and v.is_integer():
-                return str(int(v))
-            return str(v)
-
         tx = {
             "date": format_date(get_val(idx_date)),
             "amount": get_val(idx_amount),
@@ -263,10 +255,8 @@ def fetch_sheet_data(spreadsheet_id: str, credentials_path: str) -> list[dict]:
             "purpose": get_val(idx_purpose),
             "inferred_amount": get_val(idx_inferred_amount),
             "sender": get_val(idx_sender),
-            "vs": get_str(idx_vs),
             "message": get_val(idx_message),
             "bank_id": get_val(idx_bank_id),
-            "sync_id": get_val(idx_sync_id),
         }
         transactions.append(tx)
     

tests/test_app.py

@@ -129,7 +129,6 @@ class TestWebApp(unittest.TestCase):
             'date': '2026-01-01', 'amount': 750, 'person': 'Test Member',
             'purpose': '2026-01', 'message': 'test payment',
             'sender': 'External Bank User', 'inferred_amount': 750,
-            'vs': '', 'sync_id': 'abc123',
         }]
         response = self.client.get('/api/adults')
         self.assertEqual(response.status_code, 200)
@@ -156,7 +155,6 @@ class TestWebApp(unittest.TestCase):
         mock_fetch_sheet.return_value = [{
             'date': '2026-01-15', 'amount': 500, 'person': 'Junior One',
             'purpose': '2026-01', 'message': '', 'sender': 'Parent', 'inferred_amount': 500,
-            'vs': '', 'sync_id': 'def456',
         }]
         response = self.client.get('/api/juniors')
         self.assertEqual(response.status_code, 200)
@@ -174,7 +172,6 @@ class TestWebApp(unittest.TestCase):
         mock_fetch_sheet.return_value = [{
             'date': '2026-01-01', 'amount': 750, 'person': 'Test Member',
             'purpose': '2026-01', 'message': 'test', 'sender': 'Someone',
-            'vs': '', 'sync_id': 'ghi789',
         }]
         response = self.client.get('/api/payments')
         self.assertEqual(response.status_code, 200)