- Add 10-second dedup window to heartbeat mutation for idempotency
- Add frontend debouncing (5s) with refs to prevent duplicate calls
- Track pending heartbeat state to block overlapping async calls
- Early return when session already updated with same path
Backend (convex/stats.ts):
- Add HEARTBEAT_DEDUP_MS constant (10 seconds)
- Check if session was recently updated before patching
Frontend (src/hooks/usePageTracking.ts):
- Add isHeartbeatPending, lastHeartbeatTime, lastHeartbeatPath refs
- Wrap sendHeartbeat in useCallback with debounce logic
- Import useCallback from React
Fixes write conflict retries shown in Convex dashboard for stats:heartbeat
