Implement ClaimApprovalRepository with full metadata storage
epic-expense-approval-workflow-foundation-task-004 — Implement ClaimApprovalRepository using the Supabase client. Expose recordDecision(), getDecisionsForClaim(), and getPendingDecisionsForCoordinator() methods. Ensure every insert captures coordinator identity, threshold value active at decision time, and a UTC timestamp. Map domain errors from Supabase constraints to typed Dart exceptions.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 2 - 518 tasks
Can start after Tier 1 completes
Implementation Notes
getPendingDecisionsForCoordinator() should call a Supabase RPC function (e.g., get_pending_claims_for_coordinator(coordinator_id UUID)) that performs the join between expense_claims, claim_approval_decisions, and coordinator_chapter_memberships on the server side. This avoids sending the full claims table to the client. Define a PendingClaimSummary Dart model that is a lightweight projection — claim_id, submitter_name, amount, submitted_at, chapter_name — not the full claim object. The RecordDecisionRequest validation should be in the domain layer, not the repository, so that BLoC tests can verify validation without a Supabase stub.
Follow the same abstract interface + concrete implementation pattern as ClaimEventsRepository for consistency.
Testing Requirements
Unit tests: recordDecision() success returns populated model, recordDecision() with empty justification on rejection throws ValidationException before network call, error mapping for each PostgrestException code, getPendingDecisionsForCoordinator() maps RPC response correctly. Integration tests: full round-trip insert and retrieve for all three decision types, verify coordinator_snapshot stored correctly matches input, verify threshold_at_decision stored matches input, getPendingDecisionsForCoordinator() returns only claims in coordinator's chapter, cross-chapter insert attempt returns ApprovalPermissionException.
Optimistic locking in ExpenseClaimStatusRepository may produce excessive concurrency exceptions in high-volume coordinator sessions where multiple coordinators process the same queue simultaneously, causing confusing UI errors and coordinator frustration.
Mitigation & Contingency
Mitigation: Design the locking strategy with a short retry window (1-2 automatic retries with 200ms back-off) before surfacing the error to the UI. Document the concurrency model clearly so the UI layer can display a contextual 'claim was already actioned' message rather than a generic error.
Contingency: If contention remains high under load testing, switch to a last-writer-wins update with a conflict notification rather than a hard block, and log all concurrent edits for audit purposes.
FCM device tokens stored for peer mentors may be stale (app reinstalled, token rotated) causing push notifications for claim status changes to silently fail, leaving submitters unaware their claim was approved or rejected.
Mitigation & Contingency
Mitigation: Implement token refresh on every app launch and store updated tokens in Supabase. ApprovalNotificationService should fall back to in-app Realtime delivery when FCM returns an invalid-token error and should queue a token refresh request.
Contingency: If FCM delivery rates fall below acceptable thresholds in production monitoring, add a polling fallback in the peer mentor claim list screen that checks status on foreground resume.
Supabase Realtime has per-project channel and connection limits. If many coordinators and peer mentors are simultaneously subscribed across multiple screens, the project may hit quota limits causing subscription failures.
Mitigation & Contingency
Mitigation: Design RealtimeApprovalSubscription to use a single shared channel per user session rather than per-screen subscriptions. Implement subscription reference counting so channels are only opened once and reused across screens.
Contingency: Upgrade the Supabase plan tier if limits are reached, and implement graceful degradation to polling with a 30-second interval when Realtime is unavailable.