Build BiometricUnavailableBanner widget with dynamic terminology
epic-biometric-session-authentication-ui-and-lifecycle-task-007 — Implement BiometricUnavailableBanner as an inline banner/modal widget that uses the organisation's dynamic terminology system for all user-facing strings. Display a plain-language explanation of why biometrics are unavailable (hardware absent vs. not enrolled), differentiated by the reason code returned by BiometricAuthService.
Acceptance Criteria
Technical Requirements
Implementation Notes
Keep the widget stateless — it renders based solely on the reason parameter and terminology lookup. Use the existing organisation labels system (likely a provider or inherited widget) via context to resolve strings. Define BiometricUnavailableReason enum in a shared auth types file to avoid circular imports. Avoid putting business logic in the widget; the caller (BLoC/Cubit) is responsible for determining the reason.
The banner should use the `.card` design token surface colour and the warning accent token for the icon/border to be visually consistent with other alert components in the app.
Testing Requirements
Write widget tests: (1) pump BiometricUnavailableBanner(reason: BiometricUnavailableReason.hardwareAbsent) and assert the correct terminology string is rendered; (2) pump with notEnrolled reason and assert alternative string; (3) pump without onDismiss and assert no dismiss button is present; (4) pump with onDismiss callback, tap dismiss button, and assert callback is invoked. Add golden test for visual regression. Verify all Semantics labels are present using tester.ensureSemantics().
Flutter's AppLifecycleState.resumed event fires in scenarios beyond simple user-initiated app-switching: it also fires when the native biometric dialog itself dismisses and returns control to Flutter, when system alerts (low battery, notifications) temporarily cover the app, and when the app is foregrounded by a deep link. Without careful debouncing and state tracking, SessionResumeManager can trigger multiple overlapping biometric prompts or prompt immediately after a just-completed authentication, creating a confusing loop.
Mitigation & Contingency
Mitigation: Implement a state machine inside SessionResumeManager with explicit states (idle, prompting, authenticated, awaiting-fallback) and guard all prompt triggers with a state check. Add a minimum inter-prompt interval of 3 seconds. Write widget tests that simulate rapid lifecycle event sequences and verify only one prompt is shown.
Contingency: If the state machine approach proves difficult to test or maintain, replace it with a simple boolean isPromptActive flag with a debounce timer, accepting slightly less precise semantics in exchange for simpler reasoning about concurrent lifecycle events.
The BiometricPromptOverlay appears on top of the existing app content when the app resumes. If focus is not correctly transferred to the overlay and returned to the underlying screen after authentication, screen reader users (VoiceOver/TalkBack) will either be unable to interact with the prompt or will lose their navigation position in the app after authentication completes, violating WCAG 2.2 focus management requirements and creating a broken experience for Blindeforbundet users.
Mitigation & Contingency
Mitigation: Use Flutter's FocusScope and FocusTrap utilities to capture focus within the overlay on presentation and restore the previous FocusNode after dismissal. Add a live region announcement (using the accessibility live region announcer component) when the overlay appears. Include dedicated VoiceOver and TalkBack test cases in the acceptance criteria.
Contingency: If FocusTrap behaviour proves unreliable across Flutter versions, implement the overlay as a full Navigator push to a modal route rather than an overlay widget, which gives Flutter's built-in modal semantics and focus management automatic WCAG-compliant behaviour.
The BiometricUnavailableBanner needs to deep-link to biometric enrollment settings on both iOS and Android. iOS uses a single URL scheme (app-settings:) that opens the app's settings page. Android has no universal URL for biometric settings — the correct Intent action (Settings.ACTION_BIOMETRIC_ENROLL) was introduced in API 30, with different fallback actions required for API 23-29. Using the wrong action on older Android devices either crashes or navigates to an unrelated settings screen.
Mitigation & Contingency
Mitigation: Build an Android API version check into LocalAuthIntegration that selects the correct Intent action based on the runtime SDK version. Test against Android API 23, 28, and 30+ in the CI matrix. For iOS, validate that the app-settings: URL scheme is correctly declared.
Contingency: If the Android settings Intent fragmentation cannot be resolved reliably for all target API levels, fall back to navigating to the top-level Settings screen (Settings.ACTION_SETTINGS) with an overlay instruction telling the user to navigate to 'Security > Biometrics' manually, ensuring the user always has a path to resolve the issue even if the deep link is imprecise.