---
phase: 04-shared-lists-live-sync
plan: 06
type: execute
wave: 5
depends_on: ['04-02', '04-04', '04-05']
files_modified:
  - apps/api/src/routes/sse.ts
  - apps/api/src/routes/lists.ts
  - apps/api/tests/routes/lists.test.ts
  - apps/pwa/src/hooks/useListSSE.ts
  - apps/pwa/src/hooks/useListSSE.test.ts
  - apps/pwa/src/components/LiveSyncIndicator.tsx
  - apps/pwa/src/routes/ListDetail.tsx
autonomous: true
requirements: [LIST-04]
user_setup: []

must_haves:
  truths:
    - "When one member adds/checks/deletes/reorders an item, the other member's open list updates within seconds without a manual refresh"
    - "A private list's events sync to the owner's own devices (D-03) but are never delivered to a member who is not its owner (D-04)"
    - 'On SSE reconnect the client full-refetches the affected list (D-10)'
    - "After capped backoff is exhausted, the UI shows an 'Updates paused' indicator and stops hammering (D-11); polling keeps data fresh (D-12)"
  artifacts:
    - path: 'apps/api/src/routes/sse.ts'
      provides: 'GET /api/sse/lists scoped SSE stream'
      contains: '/lists'
    - path: 'apps/pwa/src/hooks/useListSSE.ts'
      provides: 'bounded-backoff EventSource wrapper invalidating React Query'
      exports: ['useListSSE']
    - path: 'apps/pwa/src/components/LiveSyncIndicator.tsx'
      provides: 'connected/reconnecting/disconnected indicator'
      min_lines: 20
  key_links:
    - from: 'apps/api/src/routes/lists.ts'
      to: 'publishListEvent'
      via: 'fan-out trigger after every successful item/list write'
      pattern: 'publishListEvent'
    - from: 'apps/api/src/routes/sse.ts'
      to: 'subscribeListEvents + getAccessibleListIds'
      via: 'scoped per-list subscription inside streamSSE'
      pattern: 'subscribeListEvents|getAccessibleListIds'
    - from: 'apps/pwa/src/hooks/useListSSE.ts'
      to: '/api/sse/lists'
      via: 'EventSource(withCredentials) → invalidateQueries'
      pattern: 'EventSource'
---

<objective>
Deliver the live-sync vertical slice (LIST-04, success criterion 3): wire the scoped SSE endpoint (`GET /api/sse/lists`), emit fan-out events from every list/item write (consuming the Plan 02 emitter), and add the bounded-backoff EventSource client hook + LiveSyncIndicator so one member's edits appear for the other within seconds — surviving a brief reconnect — without leaking private-list events (D-04).

MVP slice: this is the final capability that makes the lists "shared and live" rather than single-user. All CRUD/reorder built in Plans 03–05 becomes collaborative.

Purpose: Connect the proven scoped fan-out primitive (Plan 02) to real route writes and to a robust client (bounded backoff per D-11, full-refetch-on-reconnect per D-10, polling fallback per D-12), and prove the load-bearing no-leak invariant at the HTTP/route layer.
Output: /api/sse/lists endpoint; publishListEvent triggers in lists.ts; useListSSE hook; LiveSyncIndicator; ListDetail consumes the hook and renders the indicator.
</objective>

<execution_context>
@$HOME/.claude/gsd-core/workflows/execute-plan.md
@$HOME/.claude/gsd-core/templates/summary.md
</execution_context>

<context>
@.planning/PROJECT.md
@.planning/ROADMAP.md
@.planning/phases/04-shared-lists-live-sync/04-CONTEXT.md
@.planning/phases/04-shared-lists-live-sync/04-RESEARCH.md
@.planning/phases/04-shared-lists-live-sync/04-PATTERNS.md
@.planning/phases/04-shared-lists-live-sync/04-UI-SPEC.md
@.planning/phases/04-shared-lists-live-sync/04-VALIDATION.md
@apps/api/src/routes/sse.ts
</context>

<tasks>

<task type="auto" tdd="true">
  <name>Task 1: Scoped /api/sse/lists endpoint + fan-out triggers on every write (LIST-04, D-04/D-10)</name>
  <files>apps/api/src/routes/sse.ts, apps/api/src/routes/lists.ts, apps/api/tests/routes/lists.test.ts</files>
  <read_first>
    - apps/api/src/routes/sse.ts (existing /heartbeat streamSSE pattern — extend)
    - apps/api/src/routes/lists.ts (item/list write handlers from Plans 03–04 — add emit seams)
    - apps/api/src/lib/listEmitter.ts (publishListEvent, subscribeListEvents — Plan 02)
    - apps/api/src/lib/listAccess.ts (getAccessibleListIds — Plan 02)
    - apps/api/tests/routes/lists.test.ts (LIST-04 stub incl. private-list no-leak)
    - .planning/phases/04-shared-lists-live-sync/04-PATTERNS.md §"apps/api/src/routes/sse.ts" (the /lists endpoint pattern verbatim)
    - .planning/phases/04-shared-lists-live-sync/04-RESEARCH.md Finding 1 + Finding 3
  </read_first>
  <behavior>
    - Test: a successful POST item / PATCH item / DELETE item / list:update / list:delete causes publishListEvent to fire with the matching ListEvent type for that listId. (LIST-04)
    - Test (D-04, load-bearing): an event published for member A's PRIVATE list is NOT delivered to member B's /api/sse/lists subscription — B's accessible-list set (getAccessibleListIds) excludes it, so B never subscribes to that channel. This is the "private-list events NOT emitted to a non-owner subscriber" assertion in 04-VALIDATION.md, asserted at the route/subscription layer (Plan 02 proved it at the emitter layer).
    - Test: a member subscribed via /api/sse/lists DOES receive events for a list shared with them.
    - Test: the endpoint returns 401 when unauthenticated.
  </behavior>
  <action>
    Extend sseRouter (sse.ts) with `GET /lists` following the 04-PATTERNS pattern: resolveUserId → 401 on null; const accessibleListIds = await getAccessibleListIds(userId); inside streamSSE, for each accessible listId call subscribeListEvents(listId, handler) where the handler writes an SSE event (event: event.type, data: JSON.stringify(event)) when !stream.aborted; run a 30s heartbeat loop; on exit call every unsubscribe. (resolveUserId: reuse the lists.ts copy or import a shared helper consistently — match the existing duplication convention.)

    Add publishListEvent fan-out triggers in lists.ts after every successful write (the seams left in Plans 03–04): item:added after POST item, item:updated after PATCH item, item:deleted after DELETE item, list:updated after PATCH list, list:deleted after DELETE list. Each carries { type, listId, payload } with the minimal payload needed; the client uses events only to trigger invalidate/refetch (D-10), so payload need not be the full row.

    Mount: /api/sse/lists is already under /api/sse (sseRouter mounted in index.ts) — no index.ts change needed beyond what exists. Confirm it sits behind the OIDC/dev-bypass guard.

  </action>
  <verify>
    <automated>pnpm --filter @familysync/api exec vitest run tests/routes/lists.test.ts && grep -q "publishListEvent" apps/api/src/routes/lists.ts && grep -q "/lists" apps/api/src/routes/sse.ts && pnpm --filter @familysync/api typecheck</automated>
  </verify>
  <acceptance_criteria>
    - GET /api/sse/lists subscribes only to getAccessibleListIds channels; 401 when unauthenticated.
    - Every list/item write emits the correct ListEvent via publishListEvent.
    - The D-04 route-layer no-leak test (private list of member A not delivered to member B) is present and green.
    - typecheck passes.
  </acceptance_criteria>
  <done>Scoped SSE stream live; writes fan out to accessible subscribers only; no-leak invariant proven at the route layer.</done>
</task>

<task type="auto" tdd="true">
  <name>Task 2: useListSSE bounded-backoff hook + LiveSyncIndicator + ListDetail wiring (LIST-04, D-10/D-11/D-12)</name>
  <files>apps/pwa/src/hooks/useListSSE.ts, apps/pwa/src/hooks/useListSSE.test.ts, apps/pwa/src/components/LiveSyncIndicator.tsx, apps/pwa/src/routes/ListDetail.tsx</files>
  <read_first>
    - apps/pwa/src/hooks/useListSSE.test.ts (D-11 bounded-backoff RED stub from Plan 01)
    - apps/pwa/src/routes/ListDetail.tsx (already has refetchInterval:30000 from Plan 04)
    - .planning/phases/04-shared-lists-live-sync/04-RESEARCH.md Finding 4 (EventSource wrapper verbatim) + Pitfall 3 + Pitfall 7
    - .planning/phases/04-shared-lists-live-sync/04-PATTERNS.md §"useListSSE.ts"
    - .planning/phases/04-shared-lists-live-sync/04-UI-SPEC.md §"LiveSyncIndicator", §"Live Sync + Reconnect"
  </read_first>
  <behavior>
    - Test (D-11): with a mocked EventSource that always errors, the hook retries on the backoff schedule 250→500→1000→2000→4000→cap 8000ms and, after the capped attempts are exhausted (≥6), transitions to 'disconnected' and STOPS scheduling further reconnects.
    - Test: on a successful (mocked) open, the hook resets the attempt counter, reports 'connected', and invalidates ['list', listId] (full refetch on reconnect, D-10).
    - Test: on a received list-change event, the hook invalidates ['list', listId].
    - Test: the hook closes the EventSource and clears timers on unmount (no reconnect storm — Pitfall 3).
  </behavior>
  <action>
    Create apps/pwa/src/hooks/useListSSE.ts using the RESEARCH Finding 4 pattern verbatim: refs for the EventSource/attempt-count/timer (not state), connect() in useCallback, BACKOFF_STEPS_MS=[250,500,1000,2000,4000,8000], MAX_ATTEMPTS=length; new EventSource('/api/sse/lists',{withCredentials:true}); on open → reset attempts, onStateChange('connected'), invalidateQueries(['list',listId]); on each list-change event type → invalidateQueries(['list',listId]); on error → es.close(), if attempts≥MAX → onStateChange('disconnected') and stop, else onStateChange('reconnecting') and setTimeout(connect, backoff[attempt++]); cleanup closes es + clears timer on unmount. Convert the Plan 01 stub into these real assertions (mock EventSource).

    Create LiveSyncIndicator.tsx per UI-SPEC: connected = 8px green dot (var(--color-member-1)), reconnecting = pulsing muted dot + "Reconnecting…", disconnected = red dot + "Updates paused"; role="status" with the aria-labels from UI-SPEC; role="alert" for the disconnected state.

    Wire into ListDetail: call useListSSE({ listId, onStateChange: setSyncState }) and render LiveSyncIndicator in the header. Keep refetchInterval:30000 as the always-on polling fallback (D-12) so data stays fresh even when SSE is 'disconnected'. (Consider hoisting the single SSE connection so it does not reconnect on every list navigation — acceptable to keep it in ListDetail for Phase 4 per RESEARCH note; document the choice.)

  </action>
  <verify>
    <automated>pnpm --filter @familysync/pwa exec vitest run src/hooks/useListSSE.test.ts && pnpm --filter @familysync/pwa exec tsc --noEmit && grep -q "useListSSE" apps/pwa/src/routes/ListDetail.tsx</automated>
  </verify>
  <acceptance_criteria>
    - useListSSE.test.ts: bounded-backoff exhaustion test (D-11) and reconnect-invalidate test (D-10) are real and green.
    - Hook uses withCredentials:true and closes EventSource on error before scheduling retry (no storm).
    - LiveSyncIndicator renders connected/reconnecting/disconnected with correct ARIA.
    - ListDetail consumes the hook + renders the indicator; refetchInterval polling fallback retained.
    - PWA typecheck passes.
    - Browser check (`playwright-cli`, two contexts where feasible): in context A add an item; context B's open list reflects it within a few seconds without manual refresh. Record in SUMMARY. (Cross-device/iOS-standalone live co-edit remains a device-only manual check per 04-VALIDATION.md.)
  </acceptance_criteria>
  <done>Live co-edit works: one member's edits appear for the other within seconds, with bounded reconnect + visible paused state + polling fallback.</done>
</task>

</tasks>

<threat_model>

## Trust Boundaries

| Boundary                             | Description                                                       |
| ------------------------------------ | ----------------------------------------------------------------- |
| API publisher → SSE subscribers      | the load-bearing leak boundary (D-04)                             |
| browser EventSource → /api/sse/lists | session cookie must cross (withCredentials); endpoint behind OIDC |

## STRIDE Threat Register

| Threat ID | Category               | Component                                           | Disposition | Mitigation Plan                                                                                                                                  |
| --------- | ---------------------- | --------------------------------------------------- | ----------- | ------------------------------------------------------------------------------------------------------------------------------------------------ |
| T-04-02   | Information Disclosure | scoped-fan-out leak (D-04) — load-bearing           | mitigate    | /api/sse/lists subscribes ONLY to getAccessibleListIds channels; route-layer test asserts member B never receives member A's private-list events |
| T-04-01   | Spoofing/AuthZ         | unauthenticated SSE subscription                    | mitigate    | resolveUserId → 401; endpoint behind OIDC middleware; EventSource sends session cookie via withCredentials (Pitfall 7)                           |
| T-04-11   | Denial of Service      | EventSource reconnect storm                         | mitigate    | es.close() on error + manual bounded-backoff setTimeout; give-up after MAX_ATTEMPTS (Pitfall 3)                                                  |
| T-04-12   | Information Disclosure | over-broad event payload exposing other lists' data | mitigate    | Payload carries only { type, listId, minimal } and is per-list-channel scoped; client uses it solely to trigger invalidate/refetch (D-10)        |

</threat_model>

<verification>
<automated>pnpm --filter @familysync/api exec vitest run tests/routes/lists.test.ts && pnpm --filter @familysync/pwa exec vitest run src/hooks/useListSSE.test.ts && pnpm --filter @familysync/pwa exec tsc --noEmit</automated>
- `playwright-cli` two-context live-update check.
- D-04 route-layer no-leak test green.
</verification>

<success_criteria>

- LIST-04 satisfied: live co-edit within seconds, surviving a brief reconnect.
- D-04 no-leak proven at both emitter (Plan 02) and route (this plan) layers.
- D-10 full-refetch-on-reconnect, D-11 bounded backoff + paused indicator, D-12 polling fallback all in place.
  </success_criteria>

<artifacts_produced>
**Symbols/files this plan creates (exclude from drift verification):**

- `GET /api/sse/lists` endpoint on sseRouter (apps/api/src/routes/sse.ts)
- `publishListEvent(...)` fan-out triggers in apps/api/src/routes/lists.ts (item:added/updated/deleted, list:updated/deleted)
- `apps/pwa/src/hooks/useListSSE.ts` exporting `useListSSE` (bounded-backoff EventSource wrapper)
- `apps/pwa/src/components/LiveSyncIndicator.tsx`
- ListDetail wiring of useListSSE + LiveSyncIndicator
  </artifacts_produced>

<output>
Create `.planning/phases/04-shared-lists-live-sync/04-06-SUMMARY.md` when done.
</output>
