docs: Update backlog tasks with session progress

- task-3 (Push notifications): Marked Done, added implementation notes
- task-4 (PWA offline): Marked In Progress, documented partial impl
- task-6 (c3nav indoor): Added note about removing indoor button
- task-12 (Stale participants): Added greyed-out locations feature

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backlog/tasks/task-12 - Fix-stale-participant-sessions-showing-on-map.md

@@ -4,7 +4,7 @@ title: Fix stale participant sessions showing on map
 status: Done
 assignee: []
 created_date: '2025-12-19 18:00'
-updated_date: '2025-12-19 18:20'
+updated_date: '2026-01-02 14:29'
 labels:
   - bug
   - ux
@@ -46,4 +46,12 @@ Fix: Clean up stale participants on room load and use a persistent participant I
    - Same user returning to a room gets the same participant ID
    - Prevents creating duplicate ghost entries on each page reload
    - Falls back to temporary ID if localStorage unavailable
+
+## Update (2026-01-02)
+
+Added visual indicator for stale locations:
+- Locations older than 5 minutes are greyed out (#6b7280) with 60% opacity
+- Hover tooltip shows "[name] - last seen X min ago"
+- Dynamically updates existing markers when they become stale
+- Helps users distinguish fresh vs old location data
 <!-- SECTION:NOTES:END -->

backlog/tasks/task-3 - Add-push-notifications.md

@@ -1,9 +1,10 @@
 ---
 id: task-3
 title: Add push notifications
-status: To Do
+status: Done
 assignee: []
 created_date: '2025-12-15 19:37'
+updated_date: '2026-01-02 14:27'
 labels: []
 dependencies: []
 priority: medium
@@ -14,3 +15,39 @@ priority: medium
 <!-- SECTION:DESCRIPTION:BEGIN -->
 Implement web push notifications for friend arrivals, proximity alerts, and group activity. Include battery-friendly polling options.
 <!-- SECTION:DESCRIPTION:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+## Implementation
+
+Implemented comprehensive push notification system:
+
+1. **Web Push with VAPID** (`sync-server/server.js`)
+   - VAPID key authentication for secure push
+   - Push subscriptions stored per room
+   - Silent push for location requests
+   - Notification push for friend joins/meeting points
+
+2. **Service Worker** (`public/sw.js`)
+   - Handles push events
+   - Silent push triggers location update via postMessage
+   - Notification push shows native notifications
+   - Click handling opens room URL
+
+3. **Push Hooks** (`src/hooks/usePushNotifications.ts`)
+   - Subscribe/unsubscribe to push notifications
+   - Auto-subscribes when joining room
+   - Handles VAPID public key fetching
+
+4. **Location Request System**
+   - "Ping all" button with bell icon in friends list header
+   - Individual ping button per participant
+   - Deduplicates by name (only pings one session per user)
+   - WebSocket for online clients, push for offline
+
+5. **Background Location Sync**
+   - Automatic periodic location requests (60s interval)
+   - Service worker messages for location sync
+   - Background Sync API integration
+<!-- SECTION:NOTES:END -->

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

@@ -1,9 +1,10 @@
 ---
 id: task-4
 title: PWA offline support
-status: To Do
+status: In Progress
 assignee: []
 created_date: '2025-12-15 19:37'
+updated_date: '2026-01-02 14:28'
 labels: []
 dependencies: []
 priority: high
@@ -14,3 +15,30 @@ priority: high
 <!-- SECTION:DESCRIPTION:BEGIN -->
 Implement service worker for offline caching. Store map tiles, venue data, and room state in IndexedDB. Sync when reconnected.
 <!-- SECTION:DESCRIPTION:END -->
+
+## Implementation Notes
+
+<!-- SECTION:NOTES:BEGIN -->
+## Partial Implementation
+
+PWA basics implemented:
+
+1. **Service Worker** (`public/sw.js`)
+   - Push notification handling
+   - Location request messaging
+   - Basic caching setup
+
+2. **Install Banner** (`src/components/room/InstallBanner.tsx`)
+   - Detects installable PWA state
+   - Shows "Add to Home Screen" prompt
+   - iOS-specific instructions
+   - Dismissible with localStorage persistence
+
+3. **PWA Manifest** - App manifest with icons and theme colors
+
+## Still Needed
+- Offline map tile caching (IndexedDB)
+- Room state persistence for offline viewing
+- Sync queue for offline location updates
+- Background sync when reconnected
+<!-- SECTION:NOTES:END -->

backlog/tasks/task-6 - c3nav-indoor-integration.md

@@ -4,7 +4,7 @@ title: c3nav indoor integration
 status: Done
 assignee: []
 created_date: '2025-12-15 19:37'
-updated_date: '2025-12-17 00:44'
+updated_date: '2026-01-02 14:28'
 labels: []
 dependencies: []
 priority: high
@@ -27,4 +27,8 @@ Implemented c3nav indoor map integration:
 - Tap-to-set indoor position
 - Position sync between participants
 - Easter egg: 'The Underground of the Underground'
+
+## Update (2026-01-02)
+
+Removed indoor map button from UI because c3nav blocks iframe embedding (X-Frame-Options: deny). The C3NavEmbed component now shows a fallback UI with an 'Open c3nav' button that opens in a new tab. Indoor map functionality is effectively deprecated in favor of direct c3nav usage.
 <!-- SECTION:NOTES:END -->