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 # Bill Tracker — Changelog
 ## v0.41.0
 
+### 🔷 TypeScript foundation + branded money types
+
+- **[Client] Adopted TypeScript incrementally, starting with the money boundary** — the move off plain JS. Upgraded `jsconfig` → `tsconfig` with full `strict` + `noUncheckedIndexedAccess`, but `allowJs` + `checkJs:false` so every existing `.js`/`.jsx` keeps resolving and running untouched — only `.ts`/`.tsx` are type-checked, so it's a file-by-file migration with nothing breaking in between. Added `npm run typecheck` (`tsc --noEmit`) and wired it into `npm run ci`. Installed TypeScript 6 + `@types/react`/`react-dom` 19.
+- **[Client] Branded `Cents`/`Dollars` types** — converted `client/lib/money.js` → `money.ts` with `type Cents = number & { __unit: 'cents' }` / `type Dollars = number & { __unit: 'dollars' }` plus `asCents`/`asDollars`/`centsToDollars`/`dollarsToCents`. The formatters now require the correct branded unit (a bare number won't type-check), so a typed caller **physically cannot format cents as dollars** (the 100×-too-big bug — cf. QA-B9-01) or vice-versa. A never-imported `money.type-test.ts` guard uses `@ts-expect-error` to assert each unit mixup is a real compile error, so `typecheck` fails loudly if the branding ever regresses (verified: removing a guard makes tsc error `Argument of type 1234 is not assignable to DollarsInput`). Existing `.jsx` callers are unaffected (checkJs off). Full CI (lint + typecheck + server 181 + client 48 + build) green.
+
 ### 🧪 Money-service test coverage
 
 - **[Tests] Covered two untested money-critical services** — the manual-vs-bank payment source-of-truth (`paymentAccountingService`) and the analytics month-window math (`analyticsService`) had no dedicated tests. Added `tests/paymentAccountingService.test.js` (bank-backed predicate, the accounting-active SQL fragment, and the core invariant: a bank payment overrides a provisional manual payment so it isn't double-counted, restores the balance, and the manual payment counts again with its balance re-applied when the override is removed) and `tests/analyticsService.test.js` (month key/label/addMonths/monthEndDate/buildMonths with year-boundary + leap-year edges, and `validateSummaryQuery` defaults/range errors). (Tracker X2)