Build LiveRegionAnnouncer announcement queue
epic-screen-reader-support-core-services-task-008 — Implement the LiveRegionAnnouncer widget as a Riverpod provider-backed announcement queue. Support polite announcements (queued, played after current utterance) and assertive announcements (interrupt current speech). Use SemanticsService.announce() under the hood. Provide announce(message, priority) and announcePolite(message) APIs. Ensure the queue drains correctly when multiple announcements arrive in rapid succession.
Acceptance Criteria
Technical Requirements
Implementation Notes
Use a StateNotifier
Keep the widget itself a const StatelessWidget with a Semantics(explicitChildNodes: false) wrapper to stay invisible to the accessibility tree.
Testing Requirements
Write flutter_test unit tests using a mock SemanticsService binding. Test: (1) polite messages are queued in FIFO order, (2) assertive messages bypass the queue, (3) rapid-fire polite messages coalesce correctly, (4) empty/whitespace messages are no-ops, (5) queue is empty after draining. Use fake_async to control time-based dispatch. Aim for ≥90% branch coverage on the StateNotifier logic.
Verify provider is accessible from a ProviderScope in widget tests without throwing.
Flutter's build pipeline and SemanticsService.announce() operate asynchronously. Announcements triggered too early (before the semantic tree settles) may be swallowed silently on both platforms, causing acceptance criteria around the 500ms window to fail intermittently in CI and on device, which would block pilot launch.
Mitigation & Contingency
Mitigation: Implement the LiveRegionAnnouncer with a post-frame callback delay and an internal timing guard. Write integration tests using WidgetTester.pump() sequences that verify announcement delivery across multiple frame boundaries. Validate on physical devices at each sprint boundary, not only in CI.
Contingency: If consistent announcement timing cannot be achieved within Flutter's semantic pipeline, switch to a platform channel approach that calls native UIAccessibility.post (iOS) and AccessibilityManager.announce (Android) directly, bypassing Flutter's intermediary.
Flutter does not natively emit a focus-gain event to Dart code when VoiceOver or TalkBack moves focus to a specific widget. If the intercept mechanism for the SensitiveFieldWarningDialog relies on an unsupported or undocumented hook in the semantics tree, it may miss focus events for some field types or in some navigation contexts, leaving sensitive data unprotected.
Mitigation & Contingency
Mitigation: Prototype the focus-intercept mechanism during the first sprint of this epic, before building the dialog UI. Evaluate Flutter's SemanticsBinding.instance callbacks and custom SemanticsActions as intercept points. Document the chosen mechanism with platform compatibility notes.
Contingency: If no reliable focus-intercept is available, implement an alternative where sensitive fields show a static 'Screen reader active — tap to reveal' overlay instead of an OS dialog, which is less seamless but achieves equivalent privacy protection without relying on an unreliable event hook.
The AccessibilityTestHarness depends on internal flutter_test semantic tree APIs that can change between Flutter minor versions. If the project upgrades Flutter during this epic, the harness may break silently, causing CI accessibility tests to pass while actually skipping assertions.
Mitigation & Contingency
Mitigation: Pin the Flutter SDK version in pubspec.yaml for the duration of this epic. Document which flutter_test APIs are used and their stability tier. Add a canary test that explicitly fails if the semantic tree API surface changes.
Contingency: If a forced Flutter upgrade breaks the harness, prioritise patching the harness as a blocking task before any other epic work continues, using the canary test failure as the trigger.