Pin Sep 2025 – Feb 2026 at 750 CZK in ADULT_FEE_MONTHLY_RATE so
historical billing is unchanged; new default 700 CZK applies to
2026-04 onward. March 2026 stays at 350.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
The previous calculation derived balance from total_balance (which includes
current/future-month activity and out-of-window credits) plus a one-sided
debt-only adjustment. Current-month surplus leaked through, making the balance
appear less negative than actual past-month debt (e.g. Mauric Daniel -1250 vs
correct -1750). Pay-All is now max(0, -balance) so the two values share a
single source and cannot disagree.
Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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>
