Configure Notification Accessibility Settings
epic-push-notification-delivery-ui-task-003 — Set up the NotificationAccessibilityConfig infrastructure layer that defines merged VoiceOver and TalkBack semantic labels, WCAG 2.2 AA contrast ratios, minimum touch target sizes (48x48dp), and live region announcement strategies for all notification UI components. Export constants consumed by widget builders.
Acceptance Criteria
Technical Requirements
Implementation Notes
Create lib/features/notifications/accessibility/notification_accessibility_config.dart as a final class with only static const members. Define a private _contrastRatio(Color fg, Color bg) function using the WCAG relative luminance formula (0.2126R + 0.7152G + 0.0722B after gamma correction) to validate color pairs at test time. Group semantic labels by widget: const notificationItemLabel, const markAsReadHint, const unreadBadgeLabel, etc. For live region strategy, create a NotificationLiveRegionPolicy enum with assertive and polite values and map each announcement type to the correct policy.
Reference accessibility_preferences data model when building the contrast mode variant — if contrastMode == 'high', use higher-contrast color tokens from the design token system. This config class should be the single source of truth imported by all notification widget builders.
Testing Requirements
Unit tests (flutter_test): (1) assert all semantic label constants are non-empty strings; (2) contrast ratio utility returns true for all defined color pairs against WCAG 4.5:1 threshold; (3) minTouchTarget constant equals 48.0; (4) buildNotificationSemantics returns a Semantics widget with non-null label and correct liveRegion value. Widget test: render a NotificationListItem wrapped with the config semantics and use tester.getSemantics() to assert correct label and hint are present. No external dependencies needed — pure Flutter semantics API.
The notification badge widget depends on a persistent Supabase Realtime websocket subscription for live unread count updates. On mobile, network transitions (WiFi to cellular, background app state) can silently drop the websocket, resulting in a stale badge count that does not update until the next app foreground — reducing trust in the notification system.
Mitigation & Contingency
Mitigation: Implement connection lifecycle management in the badge widget's BLoC that re-subscribes on app foreground and on network reconnection events. Add a fallback polling query (every 60 seconds when app is foregrounded) to reconcile the badge count if the Realtime subscription is interrupted.
Contingency: If Realtime reliability proves insufficient in production, replace the live subscription with a polling approach using a configurable interval, accepting slightly delayed badge updates in exchange for reliability.
The notification list item widget requires merged semantics combining title, body, timestamp, read state, and role-context icon into a single VoiceOver/TalkBack announcement. Getting the merged semantics structure right for both iOS (VoiceOver) and Android (TalkBack) simultaneously is non-trivial and common to break silently when widgets are refactored.
Mitigation & Contingency
Mitigation: Use the project's existing semantics-wrapper-widget pattern with explicit Semantics widgets and excludeSemantics on decorative children. Write accessibility widget tests using Flutter's SemanticsController to assert the exact announcement string. Test on physical devices with VoiceOver and TalkBack enabled before release.
Contingency: If merged semantics cannot be achieved cleanly on both platforms, implement platform-specific semantic trees using defaultTargetPlatform branching, ensuring each platform receives an optimal announcement even if the implementation differs.