Implement dynamic content insertion focus placement
epic-screen-reader-support-core-services-task-005 — Add to FocusManagementService the ability to move focus to dynamically inserted content such as inline validation errors, expanded accordion sections, or newly loaded list items. Provide a moveFocusTo(GlobalKey) API that safely schedules a post-frame focus request and falls back gracefully if the target is not yet mounted. Cover async content that appears after a network delay.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 2 - 518 tasks
Can start after Tier 1 completes
Implementation Notes
The polling mechanism must use WidgetsBinding.instance.addPostFrameCallback recursively — after each frame check GlobalKey.currentContext != null. If still null, register another addPostFrameCallback. Do NOT use Timer.periodic as it fires even when no frame is scheduled, wasting CPU. Store pending requests in a List
For async Supabase content, the typical pattern is: BLoC emits loaded state → widget calls WidgetsBinding.instance.addPostFrameCallback → calls FocusManagementService.moveFocusTo(contentKey). Document this pattern in the service's dartdoc as the recommended async usage. For inline validation errors, the moveFocusTo() call should be placed in the form's onValidationFailed callback. Also expose a announceToScreenReader(String) convenience method using SemanticsService.announce() for cases where a GlobalKey target is not appropriate (e.g., transient snackbar messages).
Testing Requirements
Unit tests: verify moveFocusTo() with an immediately mounted key focuses within one frame; verify polling logic retries up to the configured limit then stops; verify queue overflow discards the oldest request. Widget tests: pump a form, trigger validation error, call moveFocusTo(errorKey), assert the error Semantics node has focus. Async tests: use flutter_test FakeAsync to simulate a 500ms Supabase delay, call moveFocusTo() before the delay, verify focus is placed after the widget appears. Edge-case tests: moveFocusTo() with a null GlobalKey logs a warning and returns immediately; moveFocusTo() when app lifecycle is paused queues the request.
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.