Establishes the server-TypeScript foundation and migrates utils/money →
utils/money.mts with branded Cents/Dollars (mirroring the client), so the
cents↔dollars boundary — the origin of the reconciliation bug class — is a
compile error for any typed server caller.
Approach (no build step): Node 25 runs .ts natively (type-stripping).
Migrated modules use the explicit-ESM .mts extension (the project is
"type":"commonjs", which disables .ts ESM auto-detection) and are required
from the CJS callers via Node's require(esm) — verified working. Infra:
tsconfig.server.json (allowJs + checkJs:false → incremental like the
client), npm run typecheck:server, check:server extended to .mts, wired
into ci. 28 require sites repointed to money.mts.
typecheck:server clean; full server suite 225 + e2e probe 17/17 green.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
The payoff simulation reported months_to_freedom by taking Math.max over each
debt's payoff month — but a debt whose minimum never overcomes its interest (and
that the rolling snowball can't cover) never reaches $0, so its "never" counted
as 0 and the projection showed the OTHER debts' last month as the freedom date.
Now months_to_freedom/payoff_date are null when any active debt never clears, the
result is flagged capped, and each such debt is marked never_paid
(services/snowballService.js + the same guard in aprService calculateMinimumOnly).
Also adds tests/snowballMath.test.js (12) — the debt-payoff engine had zero
coverage. Hand-calculated examples for amortization (0% + 12% APR), snowball
rolling, avalanche vs snowball interest, skip reasons, APR snapshot, and the
unpayable-debt edge. Server suite 151 pass.
Co-Authored-By: Claude Opus 4.8 <[email protected]>
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