Converted client/lib/money.js -> money.ts with branded types:
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 do), so a typed caller physically
cannot format cents as dollars (the 100×-too-big bug) or vice-versa. Existing
.jsx callers are unaffected (checkJs off) — gradual adoption.
money.type-test.ts is a compile-time guard (never imported/bundled): its
@ts-expect-error lines assert each unit mixup is a real 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'.
typecheck + build (with React Compiler) + 48 client tests all green.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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