---
phase: 04-shared-lists-live-sync
plan: '02'
subsystem: api-lib, test-harness
tags: [listEmitter, listAccess, scoped-fanout, D-04, tdd, eventEmitter, sse-primitive]
dependency_graph:
  requires:
    - 04-01 (lists/list_shares schema, test harness, vitest.config.ts)
  provides:
    - publishListEvent(listId, event): scoped in-process fan-out
    - subscribeListEvents(listId, handler): per-list subscription returning unsub closure
    - ListEvent type union
    - getAccessibleListIds(userId): owner OR list_shares access-scope query
    - fileParallelism:false vitest config (prevents DB test race conditions)
  affects:
    - apps/api/tests/lib/listEmitter.test.ts (stubs replaced with real assertions)
    - apps/api/vitest.config.ts (fileParallelism:false added)
tech_stack:
  added: []
  patterns:
    - Module-level EventEmitter singleton; per-list channel key list:${listId}
    - subscribeListEvents returns unsub closure (emitter.off)
    - Two-query union (owned + shared) with Set dedup for getAccessibleListIds
    - randomUUID() suffix in test seed helpers to avoid unique-key collisions
    - fileParallelism:false to serialize DB test file execution
key_files:
  created:
    - apps/api/src/lib/listEmitter.ts
    - apps/api/src/lib/listAccess.ts
    - apps/api/tests/lib/listAccess.test.ts
  modified:
    - apps/api/tests/lib/listEmitter.test.ts (it.todo stubs replaced with real assertions)
    - apps/api/vitest.config.ts (fileParallelism:false; sequence.concurrent:false)
decisions:
  - 'D-04: In-memory EventEmitter per-list channel isolation confirmed by Test 2 (cross-list negative)'
  - 'D-18: ioredis NOT introduced; abstraction boundary in listEmitter.ts makes future Redis swap mechanical'
  - 'vitest fileParallelism:false: global afterEach in test/setup.ts truncates shared MariaDB state; parallel files caused FK violations mid-test'
  - 'getAccessibleListIds: two-select + Set approach per RESEARCH Finding 3 (not single OR-join) — simpler, equally correct'
  - 'listAccess.test.ts in tests/lib/ (not src/lib/) per tdd_note convention matching listEmitter placement'
metrics:
  duration: '~15 minutes'
  completed: '2026-06-09'
  task_count: 3
  file_count: 5
---

# Phase 4 Plan 2: Scoped Fan-out Primitives Summary

**One-liner:** In-memory per-list EventEmitter singleton (listEmitter.ts) + owner/shares access-scope query (listAccess.ts) with D-04 isolation proven by RED/GREEN TDD gate.

## TDD Gate Compliance

| Gate                   | Commit    | Status                                                         |
| ---------------------- | --------- | -------------------------------------------------------------- |
| RED — failing tests    | 2d250af   | PASS — module-not-found; 6 tests failed as expected            |
| GREEN — implementation | 792efeb   | PASS — all 9 tests pass                                        |
| REFACTOR               | (skipped) | No refactoring needed — implementation was clean on first pass |

## Tasks Completed

| Task  | Name                                                 | Commit  | Files                                                                          |
| ----- | ---------------------------------------------------- | ------- | ------------------------------------------------------------------------------ |
| RED   | Write failing listEmitter + listAccess tests         | 2d250af | listEmitter.test.ts (stubs → assertions), listAccess.test.ts (new)             |
| GREEN | Implement listEmitter.ts + listAccess.ts             | 792efeb | listEmitter.ts, listAccess.ts, listAccess.test.ts (UUID fix), vitest.config.ts |
| FIX   | fileParallelism:false to eliminate DB race condition | 9e17853 | vitest.config.ts                                                               |

## Deviations from Plan

### Auto-fixed Issues

**1. [Rule 1 - Bug] Test seed helper oidc_sub collisions across runs**

- **Found during:** GREEN phase — running both test files together
- **Issue:** `seedUser('owner-5')` inserted `sub-owner-5` on first run; on the second run (or when running tests without cleanup of the users table), the `uniq_oidc_identity` key fired `ER_DUP_ENTRY`.
- **Fix:** Added `randomUUID()` suffix: `oidcSub: sub-${label}-${randomUUID()}` — unique per invocation regardless of table state.
- **Files modified:** `apps/api/tests/lib/listAccess.test.ts`
- **Commit:** 792efeb

**2. [Rule 1 - Bug] Concurrent test files race against shared-MariaDB global afterEach**

- **Found during:** GREEN phase — running both test files together (and during full suite run)
- **Issue:** vitest defaults to `fileParallelism: true`. The global `afterEach` in `test/setup.ts` runs in every worker and truncates `lists`/`listShares`. When two DB-backed test files ran concurrently, file A's `afterEach` deleted rows that file B's test was still reading — producing FK violations (`ER_NO_REFERENCED_ROW_2`) and incorrect empty results.
- **Fix:** Added `fileParallelism: false` to `vitest.config.ts`, serializing test file execution.
- **Files modified:** `apps/api/vitest.config.ts`
- **Commit:** 9e17853

## Verification Results

### TDD Tests

- listEmitter suite: 5 passed (Tests 1-4 + D-18 scale check)
- listAccess suite: 4 passed (Tests 5-8)
- **Test 2 (D-04 cross-list negative):** GREEN — handler subscribed to list 1 received 0 events when list 2 published
- **Test 7 (D-04 private-list negative):** GREEN — `getAccessibleListIds(otherUser)` did not return a list owned exclusively by another user

### Full API Suite

- 15 test files passed | 3 skipped (Wave-0 stubs, expected) | 117 passed | 38 todo
- No regressions from prior plans

### TypeScript

- `pnpm --filter @familysync/api exec tsc --noEmit` — PASS

### ioredis Check

- `grep -r "ioredis" apps/api/` — not present (D-18 confirmed)

## Known Stubs

None. Both modules are fully implemented and tested.

## Threat Surface Scan

| Flag                | File                            | Description                                                                                       |
| ------------------- | ------------------------------- | ------------------------------------------------------------------------------------------------- |
| T-04-02 (mitigated) | apps/api/src/lib/listEmitter.ts | Fan-out channel keyed by listId; cross-list isolation proven by Test 2                            |
| T-04-03 (mitigated) | apps/api/src/lib/listAccess.ts  | Access-scope query restricted to owner_id OR list_shares; over-return proven impossible by Test 7 |
| T-04-04 (accepted)  | apps/api/src/lib/listEmitter.ts | setMaxListeners(200) headroom applied; DoS risk accepted for household scale                      |

## Self-Check: PASSED

- `apps/api/src/lib/listEmitter.ts` — FOUND
- `apps/api/src/lib/listAccess.ts` — FOUND
- `apps/api/tests/lib/listEmitter.test.ts` — FOUND (stubs replaced)
- `apps/api/tests/lib/listAccess.test.ts` — FOUND
- `apps/api/vitest.config.ts` — FOUND (fileParallelism:false)
- Commit 2d250af (RED) — FOUND
- Commit 792efeb (GREEN) — FOUND
- Commit 9e17853 (fix) — FOUND
