Implement device biometric capability check
epic-biometric-session-authentication-core-services-task-002 — Implement the device capability detection logic within BiometricAuthService that queries LocalAuthIntegration to determine whether the device supports biometric authentication (Face ID, fingerprint, iris) and whether the hardware is enrolled. Returns a typed capability result distinguishing between hardware-unsupported, enrolled, and not-enrolled states.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 1 - 540 tasks
Can start after Tier 0 completes
Implementation Notes
Define a LocalAuthIntegration abstract class (or interface) in lib/data/auth/local_auth_integration.dart that wraps LocalAuthentication from flutter_local_auth. BiometricAuthService depends on this abstraction, not the concrete plugin. This inversion is critical for testability — the real platform plugin cannot be invoked in flutter_test unit tests. The concrete LocalAuthIntegrationImpl is registered in the DI container (e.g., Riverpod provider or get_it) and used only at runtime.
Sequence: call canCheckBiometrics first (cheap), then getAvailableBiometrics only if true (slightly more expensive). Wrap both calls in try/catch PlatformException. Do not call isDeviceSupported() as an additional check — canCheckBiometrics already implies device support on modern flutter_local_auth versions.
Testing Requirements
Unit tests in test/services/biometric_auth_service_test.dart using a MockLocalAuthIntegration (mocktail). Test cases: (1) canCheckBiometrics returns false → BiometricAuthUnavailable(hardwareNotSupported); (2) canCheckBiometrics true + empty biometrics list → BiometricAuthUnavailable(notEnrolled); (3) canCheckBiometrics true + [BiometricType.face] → BiometricAuthSuccess or capability-available result; (4) canCheckBiometrics throws PlatformException → BiometricAuthFailure with non-empty errorMessage. Verify no real platform calls are made by asserting MockLocalAuthIntegration interaction counts. All four paths must be covered.
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.