Implement Foreground Notification Display
epic-push-notification-delivery-engine-task-008 — Extend PushNotificationService to display local notifications when the app is in the foreground using flutter_local_notifications with configured Android and iOS channel settings. Map incoming FCM RemoteMessage to a LocalNotification with title, body, and payload. Ensure accessibility labels from NotificationAccessibilityConfiguration are applied and that the displayed notification triggers the deep link handler on tap.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 4 - 323 tasks
Can start after Tier 3 completes
Implementation Notes
Extract LocalNotificationDisplay as a separate injectable class (not nested in the BLoC) to keep the BLoC thin and testable. Use a local Set
On iOS, foreground presentation options (presentAlert etc.) must also be set via FirebaseMessaging.instance.setForegroundNotificationPresentationOptions() for FCM-delivered notifications — flutter_local_notifications handles the local re-display case.
Testing Requirements
Widget/unit tests using flutter_test and mocktail. Mock FlutterLocalNotificationsPlugin and NotificationDeepLinkHandler. Test cases: (1) foreground RemoteMessage → show() called with correct title/body, (2) RemoteMessage with null notification → defaults used, (3) tap on notification → deep link handler receives deserialized payload, (4) same message_id received twice → show() called only once, (5) Android channel created with correct importance level, (6) iOS DarwinNotificationDetails has presentAlert true. Verify WCAG 2.2 AA: notification titles must not rely solely on color to convey meaning.
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.