Implement Notification Repository
epic-push-notification-delivery-engine-task-002 — Create the NotificationRepository data layer that stores received notification records in Supabase with fields for notification_id, user_id, category, title, body, payload JSON, read_at timestamp, and created_at. Include RLS policy so users only fetch their own notifications, and expose streams for real-time unread count badges.
Acceptance Criteria
Technical Requirements
Implementation Notes
For the real-time unread count, subscribe to the Supabase Realtime postgres_changes channel filtered by user_id and event INSERT/UPDATE on the notifications table. On each event, re-query the COUNT of rows where read_at IS NULL to get an accurate server count rather than computing locally (avoids drift). Use a StreamController.broadcast() internally in the repository so multiple listeners (e.g. bottom nav badge and notification screen) can share one subscription.
Expose the stream via a Riverpod StreamProvider for easy consumption. The payload JSONB field should be typed as Map
Testing Requirements
Unit tests with mocked Supabase client: verify getNotifications constructs correct paginated query; verify markAsRead sends correct UPDATE payload; verify watchUnreadCount returns a Stream and emits updated value on simulated Realtime event. Integration tests against local Supabase: (1) user A fetches only their notifications; (2) user A cannot read user B's notifications; (3) markAsRead sets read_at and subsequent unread count stream emits decremented value; (4) stream closes without errors when subscription is cancelled. Test stream lifecycle: open stream, receive event, cancel, verify no further events. Target ≥ 90% line coverage.
Flutter's background message handler for FCM must run in a separate Dart isolate. Incorrect dependency initialization in the isolate (e.g., attempting to access Riverpod providers or Supabase before initialization) will cause silent crashes on Android when the app is terminated, resulting in missed notifications that are invisible in crash reporting.
Mitigation & Contingency
Mitigation: Use a minimal top-level background handler function annotated with @pragma('vm:entry-point') that only stores the raw RemoteMessage payload to a platform channel or shared preferences. Process the payload in the main isolate on next app launch. Write an explicit test for terminated-state message handling on Android.
Contingency: If isolate crashes are observed, implement a native Android FirebaseMessagingService subclass that handles background messages without Flutter isolate complexity, falling back to a database-insert-only approach for terminated-state notifications.
Supabase Edge Functions can experience cold-start latency of 1–3 seconds after periods of inactivity. For high-frequency events like assignment creation, cumulative cold starts could cause dispatch delays exceeding the 30-second SLA, reducing the perceived reliability of the notification system.
Mitigation & Contingency
Mitigation: Configure the Edge Function with a keep-warm ping mechanism or use Supabase database webhooks that invoke the function directly on row insert to minimize cold-start frequency. Batch preference lookups within the function to reduce per-invocation Supabase round-trips.
Contingency: If latency SLA is consistently breached, move to a polling or Realtime-subscription architecture within the Edge Function, or pre-compute dispatch targets at preference-save time to eliminate per-dispatch preference queries.
If the deep link handler does not perform server-side role validation before rendering the target screen, a peer mentor who receives a mis-configured notification payload containing a coordinator-only route could access restricted data, violating the role-based access control invariants.
Mitigation & Contingency
Mitigation: The deep link handler must check the user's current role from the RoleStateManager before constructing the navigation route. Coordinator-only routes must be listed in a deny-list checked against the current role. The go_router route guard is a second line of defence.
Contingency: If a role bypass is discovered in testing, immediately add the affected route to the deep link handler deny-list and add a regression test. Audit all notification payload types for route targets that could expose cross-role data.
FCM v1 HTTP API enforces per-project send quotas. For large organisations with many active peer mentors receiving simultaneous assignment notifications, batch dispatch events (e.g., bulk coordinator assignments) could approach quota limits and result in dropped notifications with 429 errors logged silently.
Mitigation & Contingency
Mitigation: Implement exponential backoff retry logic in the Edge Function for 429 responses. Design bulk assignment flows to dispatch notifications in batches with a configurable delay between batches. Monitor FCM console quotas during load testing.
Contingency: If quota limits are hit, implement a notification queue table in Supabase and a separate Edge Function that processes the queue with rate limiting, ensuring eventual delivery without exceeding FCM quotas.