Announce tab switches in bottom navigation overlay
epic-screen-reader-support-complex-widgets-task-007 — Extend AccessibleBottomNavigation to post a live region announcement whenever the user switches tabs. The announcement should name the newly active tab and optionally describe its context (e.g., 'Contacts tab, 3 unread'). Use LiveRegionAnnouncer to ensure announcements do not interrupt ongoing speech but queue appropriately.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Implementation Notes
The key design challenge here is avoiding double-announcement: task-006 sets Semantics.selected=true on the new tab (which VoiceOver may read as 'selected'), and this task posts a live region announcement. On iOS VoiceOver, the selected state change is typically read when the user next moves focus to the tab bar — it does NOT fire automatically on programmatic tab switches. Therefore, the live region announcement IS necessary for proactive notification. On Android TalkBack, the behaviour may differ — test empirically.
To implement debounce: use a CancelableOperation from the async package. On each tab switch event from the BLoC, cancel any pending CancelableOperation and schedule a new one with a 400ms delay. For the initial launch guard: store a bool _hasRendered initialized to false; set it to true in addPostFrameCallback on first build; only call announcer if _hasRendered is true. Inject LiveRegionAnnouncer via Riverpod, consistent with how task-003 and task-005 use it, so the same announcer instance queues across all components.
Testing Requirements
Unit tests: verify TabSwitchDebouncer cancels pending announcement when a second switch fires within 400ms; verify the final announcement is the last switch target. Verify ContextualTabLabelBuilder returns 'Contacts tab' when count is 0 and 'Notifications tab, 5 unread' when count is 5. Widget tests: mount AccessibleBottomNavigation; simulate tab switch and assert LiveRegionAnnouncer.announcePolite was called exactly once with correct string. Simulate 3 rapid tab switches and assert announcer called exactly once (debounce).
Assert no announcement fires during initial widget mount. Localisation test: switch locale to Norwegian and verify announcement format. Integration test: run full tab-switching flow with VoiceOver enabled on a physical iOS device and confirm no double-announcements. Coverage target: 85%.
Flutter does not natively enforce a focus trap within a bottom sheet or modal dialog in the semantic tree — VoiceOver and TalkBack can navigate outside the sheet to background content. Implementing a reliable focus trap requires overriding the semantic tree, which may conflict with the existing modal helper infrastructure in the app and require changes to shared components beyond this feature's scope.
Mitigation & Contingency
Mitigation: Prototype the focus trap on the first modal sheet implementation before building the remaining sheets. Evaluate Flutter's ExcludeSemantics and BlockSemantics widgets as the trap mechanism, and coordinate with the team owning the shared modal helpers to agree on a non-breaking integration point before writing production code.
Contingency: If a complete semantic focus trap cannot be implemented without breaking existing modal patterns, implement a partial solution using FocusScope with autofocus on the modal's first element and a prominent 'Return to main content' semantic action, documenting the deviation from WCAG 2.4.3 with a scheduled remediation item.
The activity wizard uses BLoC state management and the UI rebuilds the entire step widget subtree on transition. If the semantic tree is traversed by VoiceOver before the build cycle settles, focus may land on a stale or partially rendered step, causing the wrong step label or progress value to be announced. This is particularly problematic for blind users who cannot visually verify the announcement against the screen.
Mitigation & Contingency
Mitigation: Coordinate ActivityWizardStepSemantics with FocusManagementService (from the core services epic) to delay focus placement until the post-build callback confirms the new step's semantic tree is complete. Write integration tests using the AccessibilityTestHarness that assert the full announcement sequence across all five wizard steps.
Contingency: If post-build focus delay is insufficient due to async BLoC emission timing, add an explicit semantic notification barrier in the wizard cubit that emits a 'step ready' event only after the new widget tree has been marked as built, decoupling the announcement trigger from the raw state transition.
Automated WCAG contrast ratio checking on widget tree snapshots may produce false positives for gradient backgrounds, dark-mode overrides, or design token overrides that are resolved at runtime but appear as unresolvable colours at static analysis time. Excessive false positives would erode team trust in the CI gate, leading to suppression rules that also mask real violations.
Mitigation & Contingency
Mitigation: Scope the WCAGComplianceChecker to check only solid-colour backgrounds in the first iteration, explicitly excluding gradients from contrast checks with documented rationale. Design the check output to distinguish 'undetermined' (gradient/unknown) from 'fail' (solid colour below threshold) so the team can take targeted action on genuine failures only.
Contingency: If false positive rates exceed 20% of reported violations during initial CI runs, switch the CI gate from a hard build failure to a warning annotation on the pull request, combined with a mandatory manual review step, until the checker's rule set has been tuned to match actual design token values.