Implement FCM token registration on auth sign-in
epic-push-notification-delivery-foundation-task-007 — In the FCMTokenManager, implement registerTokenOnSignIn(userId) that retrieves the current FCM token via FirebaseMessaging.instance.getToken(), computes a device fingerprint, and upserts the record into fcm_tokens via Supabase. Call this method in the auth state listener immediately after a successful sign-in event. Handle cases where permission has not yet been granted (defer token fetch).
Acceptance Criteria
Technical Requirements
Execution Context
Tier 2 - 518 tasks
Can start after Tier 1 completes
Implementation Notes
Place FCMTokenManager in lib/notifications/fcm_token_manager.dart as a Riverpod AsyncNotifier or plain service class. Compute device fingerprint by hashing (SHA-256) a concatenation of: Platform.operatingSystem + DeviceInfoPlugin model string + a UUID stored in FlutterSecureStorage on first install. This is stable across app updates but resets on reinstall — acceptable for token management. Listen to auth state changes via supabase.auth.onAuthStateChange stream in a Riverpod provider (ref.listen) and call registerTokenOnSignIn inside the AuthChangeEvent.signedIn branch.
Wrap the getToken() call in a try-catch because it can throw on devices where Firebase is not properly configured. Use Supabase's upsert with onConflict: 'user_id,device_fingerprint' — ensure the database has a UNIQUE constraint on those two columns before deploying.
Testing Requirements
Unit tests (flutter_test + mockito): mock FirebaseMessaging.getToken() returning a valid token, verify upsert payload structure; mock getToken() returning null, verify no exception and no Supabase call. Integration test (Supabase local/staging): sign in a test user, call registerTokenOnSignIn, query fcm_tokens and assert row exists with correct fields. Edge case test: call registerTokenOnSignIn twice for same user/device and confirm only one row exists (upsert idempotency). Security test: confirm RLS rejects an insert attempt using a different user's JWT.
iOS only allows one system permission prompt per app install. If the rationale dialog timing or content is wrong the user may permanently deny permissions during onboarding, permanently blocking push delivery for that device with no recovery path short of manual system settings navigation.
Mitigation & Contingency
Mitigation: Design and user-test the rationale dialog content and trigger point (after onboarding value-demonstration step, not at first launch). Implement the settings-deep-link fallback in NotificationPermissionManager so the permission state screen always offers a path to system settings if denied.
Contingency: If denial rates are high in TestFlight testing, revise the rationale copy and trigger timing before production release. Ensure the in-app notification centre provides full value without push so denied users are not blocked from the feature.
FCM token rotation callbacks can fire at any time, including during app termination or network outage. If the token rotation is not persisted reliably the backend trigger service will dispatch to a stale token, resulting in silent notification failures that are hard to diagnose.
Mitigation & Contingency
Mitigation: Persist token rotation updates with a local queue that retries on next app foreground if network is unavailable. Use Supabase upsert by (user_id, device_id) to prevent duplicate token rows and ensure the latest token always wins.
Contingency: If token staleness is observed in production, add a token validity check on each app foreground and force a re-registration if the stored token does not match the FCM-reported current token.
Incorrect RLS policies on notification_preferences or fcm_tokens could expose one user's preferences or device tokens to another user, or could block the backend Edge Function service role from reading token lists needed for dispatch, silently dropping all notifications.
Mitigation & Contingency
Mitigation: Write explicit RLS policy tests using the Supabase test harness covering user-scoped read/write, service-role read for dispatch, and cross-user access denial. Review policies during code review with a security checklist.
Contingency: Maintain a rollback migration that reverts the RLS changes, and add an integration test in CI that asserts the service role can query all tokens and that a normal user JWT cannot access another user's token rows.