fix: Distribute multi-month payments by per-month expected fee

reconcile() previously split a multi-month payment evenly across months,
which falsely flagged months as underpaid when their expected fees
differed (e.g. 1250 CZK for 02+03+04 2026 with rates 750/350/150 was
shown as 416/month with two months red).

The allocation now runs per matched member: greedy when the share covers
the total expected (each month gets its expected fee, surplus -> credit),
proportional by expected fee otherwise. Out-of-window months keep the
previous even-split-to-credit behavior. 6 new test cases.

Also adds CHANGELOG.md and a changelog convention in CLAUDE.md.

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

CHANGELOG.md

@@ -0,0 +1,8 @@
+# Changelog
+
+## 2026-05-03 19:26 CEST — Fee-aware allocation for multi-month payments
+
+- `reconcile()` no longer splits a multi-month payment evenly. Allocation is now per-member with two phases: greedy (if amount ≥ total expected, each month gets exactly its expected fee and overflow → credit) and proportional (otherwise distribute by each month's expected). Fixes the case where e.g. 1250 CZK covering 3 months with mixed fees (750/350/150) marked two months red.
+- Out-of-window months keep the previous even-split-to-credit behavior. Fallback to even split when all matched months have `expected = 0` (prepayment before attendance is recorded).
+- Display layer only — no changes to how payments are stored in Google Sheets; `Inferred Amount` still holds the full bank amount.
+- Files: [scripts/match_payments.py](scripts/match_payments.py), [tests/test_reconcile_exceptions.py](tests/test_reconcile_exceptions.py) (6 new test cases).

CLAUDE.md

@@ -16,22 +16,95 @@ Flask-based financial management system for FUJ (Frisbee Ultimate Jablonec). Han
 This project uses `uv` for dependency management.
 
 ```bash
-uv venv          # Create virtual environment
-uv sync          # Install dependencies from pyproject.toml
+uv venv && uv sync
 source .venv/bin/activate
 ```
 
-Alternatively, use the Makefile:
-- `make sync`      - Sync bank transactions to Google Sheets
-- `make infer`     - Automatically infer Person/Purpose/Amount in the sheet
-- `make reconcile` - Generate balance report from Google Sheets data
-- `make fees`      - Calculate expected fees from attendance
-- `make match`     - (Legacy) Match bank data directly
-- `make web`       - Start dashboard
-- `make image`     - Build Docker image
+Set `PYTHONPATH=scripts:.` when running scripts directly (the Makefile does this automatically).
 
-Requires `.secret/fuj-management-bot-credentials.json` for Google Sheets API access (configurable via `CREDENTIALS_PATH` env var).
+## Commands
+
+```bash
+make web          # Start dashboard at http://localhost:5001
+make web-debug    # Same with FLASK_DEBUG=1
+make test         # Run all tests (unittest discover)
+make test-v       # Tests with verbose output
+make fees         # Print fee report from attendance sheet
+make sync-2026    # Sync Fio bank transactions for 2026 to Google Sheets
+make infer        # Auto-fill Person/Purpose/Amount columns in payments sheet
+make reconcile    # Print balance report from Google Sheets data
+make image        # Build Docker image
+```
+
+Run a single test:
+```bash
+PYTHONPATH=scripts:. python -m unittest tests.test_app.TestWebApp.test_adults_route
+```
+
+## Architecture
+
+### Data flow
+
+```
+Google Sheets (attendance) ──► attendance.py ──► reconcile() ──► Flask routes ──► templates/
+Google Sheets (payments)   ──► match_payments.py ──┘
+Fio Bank API               ──► sync_fio_to_sheets.py ──► Google Sheets (payments)
+```
+
+### Key modules
+
+- `app.py` — Flask app; routes for `/adults`, `/juniors`, `/payments`, `/sync-bank`, `/qr`, `/flush-cache`
+- `scripts/attendance.py` — Fetches attendance CSV from Google Sheets, computes per-member per-month fees. Contains fee rate constants (`ADULT_FEE_DEFAULT`, `JUNIOR_FEE_DEFAULT`) and `ADULT_MERGED_MONTHS` / `JUNIOR_MERGED_MONTHS` dicts.
+- `scripts/match_payments.py` — `reconcile()` matches transactions to members/months. `fetch_sheet_data()` reads the payments sheet. `fetch_exceptions()` reads the `exceptions` tab.
+- `scripts/cache_utils.py` — Invalidation via Google Drive API `modifiedTime`; falls back to 5-minute TTL buckets when Drive API is unavailable. Cache files live in `tmp/`.
+- `scripts/sync_fio_to_sheets.py` — Pulls Fio bank transactions and appends them to the payments Google Sheet.
+- `scripts/infer_payments.py` — Fills in Person/Purpose/Inferred Amount columns using name-matching heuristics.
+- `scripts/config.py` — All external IDs, paths, and tunable TTLs. Override via env vars (`CREDENTIALS_PATH`, `BANK_ACCOUNT`, `CACHE_TTL_SECONDS`).
+
+### 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)
+- `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)
+- 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))`.
+
+### Merged months
+
+`ADULT_MERGED_MONTHS` / `JUNIOR_MERGED_MONTHS` in `attendance.py` map a source month to a target month (e.g., `"2025-12": "2026-01"` merges December into January billing). The target month accumulates attendance from both months.
+
+### Caching
+
+`get_cached_data()` in `app.py` checks the Drive API `modifiedTime` before each request and serves a JSON file from `tmp/` when the sheet hasn't changed. Cache is warmed up at startup (`warmup_cache()`). Flush via `/flush-cache` (POST) or `flush_cache()`.
+
+### Payments sheet columns
+
+`Date | Amount | manual fix | Person | Purpose | Inferred Amount | Sender | VS | Message | Bank ID | Sync ID`
+
+`Person` and `Purpose` are written by `infer_payments.py` and can be manually corrected. `manual fix` column presence disables re-inference for that row. Multiple people or months are comma-separated in Person/Purpose.
+
+### QR codes
+
+`/qr?account=…&amount=…&message=…` generates a Czech QR Platba PNG (SPD format).
 
 ## Git Commits
 
-When making git commits, always append yourself as co-author trailer to the end of the commit message to indicate AI assistance
+When making git commits, always append yourself as co-author trailer to the end of the commit message to indicate AI assistance
+
+## Changelog
+
+Maintain a running changelog in `CHANGELOG.md` at the repo root. After every significant change, fix, or update — once the user confirms it works — append a new entry **at the top** of the file in this format:
+
+```markdown
+## YYYY-MM-DD HH:MM TZ — short title
+
+- One-line summary of what changed and why.
+- Key files touched (optional, only if useful for traceability).
+```
+
+Get the timestamp with `date "+%Y-%m-%d %H:%M %Z"`. Skip trivial edits (typos, formatting, comment tweaks); only log changes a future reader would care about.

scripts/match_payments.py

@@ -385,8 +385,7 @@ def reconcile(
                     })
             continue
 
-        num_allocations = len(matched_members) * len(matched_months)
-        per_allocation = amount / num_allocations if num_allocations > 0 else 0
+        member_share = amount / len(matched_members) if matched_members else 0
 
         for member_name, confidence in matched_members:
             if member_name not in ledger:
@@ -397,20 +396,64 @@ def reconcile(
                 unmatched.append(tx)
                 continue
 
-            for month_key in matched_months:
-                entry = {
-                    "amount": per_allocation,
-                    "date": tx["date"],
-                    "sender": tx["sender"],
-                    "message": tx["message"],
-                    "confidence": confidence,
-                }
-                if month_key in ledger[member_name]:
-                    ledger[member_name][month_key]["paid"] += per_allocation
-                    ledger[member_name][month_key]["transactions"].append(entry)
-                else:
-                    # Future month — track as credit
-                    credits[member_name] = credits.get(member_name, 0) + int(per_allocation)
+            in_window = [(m, ledger[member_name][m]["expected"]) for m in matched_months if m in ledger[member_name]]
+            out_of_window = [m for m in matched_months if m not in ledger[member_name]]
+
+            # Out-of-window months (outside display range): even split → credit, same as before.
+            n_total = len(matched_months)
+            if out_of_window and n_total > 0:
+                out_credit = member_share / n_total * len(out_of_window)
+                credits[member_name] = credits.get(member_name, 0) + int(out_credit)
+            else:
+                out_credit = 0.0
+
+            in_window_share = member_share - out_credit
+
+            if not in_window:
+                continue
+
+            total_expected = sum(e for _, e in in_window)
+
+            if total_expected > 0 and in_window_share >= total_expected:
+                # Greedy phase: payment covers all in-window fees; overflow → credit.
+                credits[member_name] = credits.get(member_name, 0) + int(in_window_share - total_expected)
+                for m, exp in in_window:
+                    alloc = float(exp)
+                    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,
+                    })
+            elif total_expected > 0:
+                # Proportional phase: distribute in_window_share by each month's expected fee.
+                # Last month absorbs any float remainder so the sum equals in_window_share exactly.
+                remaining = in_window_share
+                for i, (m, exp) in enumerate(in_window):
+                    alloc = remaining if i == len(in_window) - 1 else in_window_share * exp / total_expected
+                    remaining -= alloc
+                    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,
+                    })
+            else:
+                # Fallback: no expected fees (prepayment before attendance recorded); even split.
+                per_month = in_window_share / len(in_window)
+                for m, _ in in_window:
+                    ledger[member_name][m]["paid"] += per_month
+                    ledger[member_name][m]["transactions"].append({
+                        "amount": per_month,
+                        "date": tx["date"],
+                        "sender": tx["sender"],
+                        "message": tx["message"],
+                        "confidence": confidence,
+                    })
 
     # Calculate final total balances (window + off-window credits)
     final_balances: dict[str, int] = {}

tests/test_reconcile_exceptions.py

@@ -52,5 +52,108 @@ class TestReconcileWithExceptions(unittest.TestCase):
         alice_data = result['members']['Alice']
         self.assertEqual(alice_data['months']['2026-01']['expected'], 750, "Should fallback to attendance fee")
 
+def _tx(person, purpose, amount):
+    return {
+        'date': '2026-01-01',
+        'amount': amount,
+        'person': person,
+        'purpose': purpose,
+        'inferred_amount': amount,
+        'sender': 'Sender',
+        'message': 'fee',
+    }
+
+
+class TestMultiMonthAllocation(unittest.TestCase):
+    """Fee-aware allocation across multiple months in a single payment."""
+
+    def test_greedy_exact_match(self):
+        """Payment equals total expected → every month fully covered (green)."""
+        members = [('Alice', 'A', {'2026-02': (750, 3), '2026-03': (350, 3), '2026-04': (150, 2)})]
+        sorted_months = ['2026-02', '2026-03', '2026-04']
+        tx = _tx('Alice', '2026-02, 2026-03, 2026-04', 1250)
+
+        result = reconcile(members, sorted_months, [tx])
+        months = result['members']['Alice']['months']
+
+        self.assertEqual(int(months['2026-02']['paid']), 750)
+        self.assertEqual(int(months['2026-03']['paid']), 350)
+        self.assertEqual(int(months['2026-04']['paid']), 150)
+
+    def test_greedy_overpayment_goes_to_credit(self):
+        """Payment exceeds total expected → each month fully covered, surplus → credit."""
+        members = [('Alice', 'A', {'2026-01': (750, 3), '2026-02': (750, 3)})]
+        sorted_months = ['2026-01', '2026-02']
+        tx = _tx('Alice', '2026-01, 2026-02', 2000)
+
+        result = reconcile(members, sorted_months, [tx])
+        months = result['members']['Alice']['months']
+
+        self.assertEqual(int(months['2026-01']['paid']), 750)
+        self.assertEqual(int(months['2026-02']['paid']), 750)
+        self.assertEqual(result['credits'].get('Alice', 0), 500)
+
+    def test_proportional_underpayment(self):
+        """Payment < total expected → proportional split; sum of paid == payment amount."""
+        members = [('Alice', 'A', {'2026-02': (750, 3), '2026-03': (350, 3), '2026-04': (750, 3)})]
+        sorted_months = ['2026-02', '2026-03', '2026-04']
+        amount = 1250
+        tx = _tx('Alice', '2026-02, 2026-03, 2026-04', amount)
+
+        result = reconcile(members, sorted_months, [tx])
+        months = result['members']['Alice']['months']
+
+        paid_02 = months['2026-02']['paid']
+        paid_03 = months['2026-03']['paid']
+        paid_04 = months['2026-04']['paid']
+
+        # All months should be partial (underpaid)
+        self.assertLess(paid_02, 750)
+        self.assertLess(paid_03, 350)
+        self.assertLess(paid_04, 750)
+        # Sum must equal the original payment (no CZK lost)
+        self.assertAlmostEqual(paid_02 + paid_03 + paid_04, amount, places=2)
+        # 02 and 04 have equal expected → equal allocation
+        self.assertAlmostEqual(paid_02, paid_04, places=2)
+
+    def test_single_month_unchanged(self):
+        """Single-month payment: full amount goes to that month (regression guard)."""
+        members = [('Alice', 'A', {'2026-01': (750, 3)})]
+        sorted_months = ['2026-01']
+        tx = _tx('Alice', '2026-01', 750)
+
+        result = reconcile(members, sorted_months, [tx])
+        self.assertAlmostEqual(result['members']['Alice']['months']['2026-01']['paid'], 750, places=2)
+
+    def test_two_members_multi_month(self):
+        """Two members, 2 months: each member gets member_share, then fee-aware per month."""
+        members = [
+            ('Alice', 'A', {'2026-01': (750, 3), '2026-02': (350, 3)}),
+            ('Bob',   'A', {'2026-01': (750, 3), '2026-02': (350, 3)}),
+        ]
+        sorted_months = ['2026-01', '2026-02']
+        # Both members pay together; total expected per member = 1100
+        tx = _tx('Alice, Bob', '2026-01, 2026-02', 2200)
+
+        result = reconcile(members, sorted_months, [tx])
+
+        for name in ('Alice', 'Bob'):
+            months = result['members'][name]['months']
+            self.assertAlmostEqual(months['2026-01']['paid'], 750, places=2)
+            self.assertAlmostEqual(months['2026-02']['paid'], 350, places=2)
+
+    def test_fallback_even_split_when_no_expected(self):
+        """All matched months have expected=0 → falls back to even split."""
+        members = [('Alice', 'A', {'2026-01': (0, 0), '2026-02': (0, 0)})]
+        sorted_months = ['2026-01', '2026-02']
+        tx = _tx('Alice', '2026-01, 2026-02', 300)
+
+        result = reconcile(members, sorted_months, [tx])
+        months = result['members']['Alice']['months']
+
+        self.assertAlmostEqual(months['2026-01']['paid'], 150, places=2)
+        self.assertAlmostEqual(months['2026-02']['paid'], 150, places=2)
+
+
 if __name__ == '__main__':
     unittest.main()