Implement BiometricAuthBloc state machine
epic-biometric-session-authentication-core-services-task-006 — Implement the Bloc/Cubit state machine that models the complete biometric authentication flow with states: idle, prompting (native dialog active), success, failed (with retry count), unavailable (hardware missing or not enrolled), and fallback-required (lockout exceeded). Emits states consumed by BiometricAuthScreen and BiometricPromptOverlay UI components.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 5 - 253 tasks
Can start after Tier 4 completes
Implementation Notes
Use Cubit over full Bloc if the event set is simple (≤5 events) — Cubit reduces boilerplate. Seal states using Dart 3 sealed classes or the freezed package for exhaustive pattern matching in UI. Keep the Bloc thin: delegate all business logic to BiometricAuthService — the Bloc only orchestrates state transitions. Use Equatable on all state classes to prevent unnecessary UI rebuilds.
For the accessibility announcement, trigger a platform channel call or use the semantics framework in the Prompting entry action. Scope the Bloc provider to the auth route using BlocProvider scoped to the navigator subtree — do not place it at the app root. Consider emitting a transient BiometricAuthState.tokenRefreshing sub-state between Prompting and Success if the token refresh is slow, to give the UI a loading indicator opportunity.
Testing Requirements
Use bloc_test package for all state machine tests. Test every valid transition path: Idle→Prompting→Success, Idle→Prompting→Failed(1), Failed(1)→Prompting→Failed(2), Idle→Unavailable, Prompting→FallbackRequired. Test reset event from every non-Idle state. Test that duplicate state emission is suppressed.
Test accessibility announcement side effect fires on Prompting transition. Aim for 100% state/event coverage. Use mockito or mocktail to mock BiometricAuthService.
Multiple concurrent callers (e.g., SessionResumeManager and a background sync service) could simultaneously detect a near-expired token and each invoke SupabaseSessionManager.refreshSession(), causing duplicate refresh API calls and potentially a token invalidation race condition on the Supabase Auth server. This can result in one caller receiving a valid refreshed token while another receives a 401, causing intermittent authentication failures.
Mitigation & Contingency
Mitigation: Implement a single-flight pattern inside SupabaseSessionManager so that concurrent refresh calls coalesce into one in-flight request. Use a Dart Completer or AsyncMemoizer to ensure all waiters receive the same refreshed token. Write a concurrent integration test to validate the single-flight behaviour.
Contingency: If the single-flight pattern introduces deadlocks or timeout complexity, fall back to a mutex-based lock with a 10-second timeout, logging a warning if the lock is held longer than expected, and triggering a full re-login if the refresh ultimately fails.
Supabase Row-Level Security policies evaluate the JWT claims (user_id, role, org_id) on every query. If the refreshed token contains stale or changed claims — for example if a coordinator's role was updated server-side — RLS may silently block data access even though the session appears valid from the client's perspective, causing confusing empty screens rather than an authentication error.
Mitigation & Contingency
Mitigation: After every token refresh, decode the new JWT and compare key claims (role, org_id) with the cached values. If claims have changed, emit a session-claims-changed event that triggers a role re-resolution and navigation reset. Document this behaviour in the SupabaseSessionManager API contract.
Contingency: If claims drift is detected in production and causes data visibility issues, provide a force-refresh mechanism in the UI (pull-to-refresh on home screen) that clears cached role state and re-fetches from Supabase, accompanied by a user-visible toast indicating the session was refreshed.
Allowing session resumption from cached local token when offline introduces a window where a revoked or invalidated session can still grant app access. For example, if a coordinator deactivates a peer mentor's account while the mentor is offline, the mentor continues to have access until connectivity is restored and the token is validated server-side.
Mitigation & Contingency
Mitigation: Set a maximum offline grace period (e.g., 24 hours) stored alongside the token in SecureSessionStorage. If the grace period is exceeded, force a full credential re-login regardless of connectivity status. Scope offline access to read-only operations only, requiring connectivity for any write that reaches Supabase.
Contingency: If the offline grace period logic is found to be insufficient for compliance, implement remote session invalidation via a lightweight push notification that clears SecureSessionStorage even when the app is backgrounded, using FCM with a data-only message.