[WalksWithASwagger]

Closes #18.

Outcome

Film Club create/join/submit/delete no longer use unconstrained whole-room read/modify/write. Routes call a small atomic store API so concurrent successful writes are preserved, capacity and create-if-absent are enforced in the mutation, and a submit racing a delete cannot resurrect a room.

Stored history is unchanged: same room:{code} keys, same room JSON shape, no TTL, no key migration, no production rewrite.

Approach

• Memory store: per-code lock plus cloned snapshots.
• Redis: Upstash REST cannot WATCH, so this uses the official equivalent compare-and-set path — SET NX for create-if-absent, and a bounded Lua CAS (createScript / EVALSHA). Lua does not re-encode rooms with cjson, so empty arrays and existing critiques are not rewritten by the script.
• Authorization (member token / owner token) is rechecked inside the mutation.
• Submit still 404s/403s before rate-limit, matching the previous client-facing order, then writes atomically.
• Bounded retries only: 5 create-code attempts, 8 CAS attempts. Failures return 409/503 without logging private payloads.
• Production unconfigured-store behavior is unchanged (isStoreConfigured()).

Route consumers enumerated

Route	Old write API	New API
GET /api/club/rooms/[code]	get	get (detached snapshot)
POST /api/club/rooms	get + set	createIfAbsent
POST .../join	get + set	joinMember
POST .../submit	get + set (could fall back to a stale room after delete)	appendSubmission
DELETE /api/club/rooms/[code]	get + del	deleteIfOwner

set/del are no longer on the write API.

Tests

Deterministic interleavings covered at store and actual route level: join/join, submit/submit, join/submit, submit/delete, create collision, duplicate member update, capacity race, snapshot isolation, legacy critique readability, CAS retry/conflict, and safe unavailable errors.

The Redis path is exercised by an in-process CAS fake (SET NX + Lua-shaped compare-and-set). That is not live Redis concurrency evidence.

Focused command:

npx tsx --test tests/club-store.test.ts tests/club-rooms.test.ts tests/club-submit.test.ts

Verification

Check	Result
npm run typecheck	pass
npm run lint	pass
npm test	pass, 63 Node tests
Focused Club tests	pass, 34 tests (memory + fake CAS + routes + 1 Redis skip)
npm run build	pass
npm run test:browser	pass, 36 Chromium checks (desktop + mobile). First attempt needed npx playwright install chromium in this environment.
Redis integration (CLUB_TEST_REDIS_URL + CLUB_TEST_REDIS_TOKEN + CLUB_TEST_NAMESPACE)	unverified — no dedicated test Redis in this environment. Memory-only and fake-CAS passes are not Redis concurrency evidence. Command and skip are documented in docs/film-club.md.

Smoke/search checks were not run; #18 does not require them and they need a live server.

Hard gates

• No data migration or history rewrite.
• No secrets committed or logged.
• Do not merge under this packet.

Rollback

A code revert restores the old racy writers against the same keys and shape. It does not rewrite stored rooms. Rooms mutated after deploy are still valid legacy JSON.

  

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Project	Deployment	Actions	Updated
wedges	Ready	Preview	Sep 20, 2026 10:57pm UTC

[WalksWithASwagger]

Duplicate of #28 (already merged; Closes #18). Closing this later draft as superseded.