Add fake payments API

[zergzorg]

/claim #1

Summary

• adds an in-memory fake payment model with pending, completed, canceled, and failed lifecycle states
• adds Winterspec routes for send, list, get, complete, cancel, and fail
• supports idempotency keys on /payments/send so retried fake payment requests do not create duplicates
• keeps terminal payments immutable, so completed/canceled/failed fake payments are not mutated by later lifecycle calls
• documents the fake payment endpoints in the README

Verification

• bun test tests/routes/payments.test.ts
• bun test
• bunx biome check lib/db/schema.ts lib/db/db-client.ts lib/payments/response-schemas.ts routes/payments tests/routes/payments.test.ts README.md
• bun run build
• ./node_modules/.bin/tsc --noEmit
• git diff --check

Follow-up check, 2026-05-23

• Re-ran bun test tests/routes/payments.test.ts: 5 passed, covering send/list, idempotency replay, get/complete, terminal-state protection, and failed-payment filtering.

Notes

This is intentionally a fake in-memory API only. It does not process real payments, call external payment services, or include any payout/private data.

[zergzorg]

Follow-up after comparing current #1 attempts:

• Added a failed terminal payment status and POST /payments/fail, giving the fake payment lifecycle pending/completed/canceled/failed states.
• Covered failed payments through the existing list filter path so callers can inspect failed fake payments by status/repository.
• Updated README endpoint notes.

Validation:

• bun test tests/routes/payments.test.ts — passed, 5 tests.
• bun test — passed, 7 tests.
• bunx biome check README.md lib/db/schema.ts lib/db/db-client.ts lib/payments/response-schemas.ts routes/payments tests/routes/payments.test.ts — passed.
• bun run build — passed.
• ./node_modules/.bin/tsc --noEmit — passed.
• git diff --check — passed.

Still fake-only: no external payment processor, payout data, or private data is involved.

[zergzorg]

Follow-up after comparing newer same-issue lifecycle attempts:

• Kept the fallback withDb database process-scoped instead of recreating it whenever route context lacks an injected db.
• This protects the live/dev payment flow from losing in-memory fake payments between send, list, get, and status-transition requests.
• Added middleware regression coverage for both fallback-db reuse and preserving an outer test-provided db.

Validation after the push:

• bun test tests/middleware/with-db.test.ts tests/routes/payments.test.ts
• bun test
• bunx biome check lib/middleware/with-db.ts tests/middleware/with-db.test.ts tests/routes/payments.test.ts
• bunx tsc --noEmit
• bun run build
• git diff --check