Mark PWA offline support task as done

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backlog/tasks/task-4 - PWA-offline-support.md

@@ -1,10 +1,10 @@
 ---
 id: task-4
 title: PWA offline support
-status: In Progress
+status: Done
 assignee: []
 created_date: '2025-12-15 19:37'
-updated_date: '2026-01-02 14:28'
+updated_date: '2026-01-02 16:15'
 labels: []
 dependencies: []
 priority: high
@@ -41,4 +41,27 @@ PWA basics implemented:
 - Room state persistence for offline viewing
 - Sync queue for offline location updates
 - Background sync when reconnected
+
+## Offline Support Completed
+
+Implemented comprehensive PWA offline support:
+
+1. **Multi-Strategy Service Worker Caching**:
+   - App shell precaching for instant loading
+   - Map tiles cache-first with background refresh (max 500 tiles)
+   - API requests network-first with cache fallback
+   - Static assets stale-while-revalidate
+
+2. **IndexedDB Room State Persistence**:
+   - saveRoomState() and getRoomState() for offline storage
+   - Room state sync in useRoom hook
+   - Saves state to SW on changes
+   - Loads cached state on initial load for offline fallback
+
+3. **Message Handlers**:
+   - SAVE_ROOM_STATE - persist room data
+   - GET_ROOM_STATE - retrieve cached data
+   - CLEAR_CACHES - manual cache clearing
+
+Deployed to production on 2026-01-02.
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