Configure flutter_local_notifications accessibility channels
epic-push-notification-delivery-foundation-task-006 — Set up flutter_local_notifications with named Android notification channels: activity_reminders (importance: high, sound: default), certification_alerts (importance: max, sound: alert), pause_status (importance: default), scenario_prompts (importance: default), and system_alerts (importance: high). Configure iOS categories with UNNotificationAction for mark-as-read. Ensure all channel descriptions are screen-reader friendly and meet WCAG 2.2 AA requirements.
Acceptance Criteria
Technical Requirements
Implementation Notes
Create a NotificationChannelConfig class (lib/notifications/channel_config.dart) with static const definitions for each channel ID and metadata. Call FlutterLocalNotificationsPlugin().initialize() inside a dedicated NotificationSetupService.init() method invoked from main() before runApp(). For iOS, pass the DarwinInitializationSettings with notificationCategories list. Use const strings for all channel IDs to prevent typo-driven mismatches at call sites.
Android channel descriptions must be set at first registration — they cannot be updated after creation without deleting and recreating the channel, so get them right from the start. Avoid using emoji or special Unicode characters in descriptions as TalkBack may read them as 'unknown character'. Bundle a short alert sound file (e.g. alert.aiff / alert.mp3) in android/app/src/main/res/raw/ for the certification_alerts channel.
Testing Requirements
Unit tests (flutter_test): verify AndroidNotificationChannel constructor arguments for all five channels; verify iOS category/action identifiers are correct strings. Widget test: confirm FlutterLocalNotificationsPlugin.initialize() is called exactly once during app startup. Manual QA checklist: open device notification settings and confirm channel labels are human-readable; activate TalkBack/VoiceOver and verify channel descriptions are announced correctly; trigger a test notification on each channel and verify sound/importance behaviour matches spec.
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.