Implement approved-to-exported state transition
epic-expense-approval-workflow-core-logic-task-005 — Implement markAsExported() on ApprovalWorkflowService. Validates the claim is in the approved state, updates status to exported via ExpenseClaimStatusRepository, records the export actor and timestamp, and guards against double-export by rejecting calls on already-exported claims with a domain exception.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 3 - 413 tasks
Can start after Tier 2 completes
Implementation Notes
Implement as a pure domain method on ApprovalWorkflowService using the FSM pattern established in previous tasks. The guard check should be a single synchronous condition evaluated before any async repository call — fail fast. Use a sealed class or enum-based result type for the return value so callers cannot ignore the error branch. The export actor timestamp must be captured as DateTime.now().toUtc() inside the service, not passed in from outside, to prevent timestamp forgery.
Wire the status update as a single Supabase `.update()` call with a `.eq('status', 'approved')` conditional filter — this provides optimistic locking at the database level and prevents TOCTOU races without needing explicit transactions.
Testing Requirements
Unit tests using flutter_test with mocked ExpenseClaimStatusRepository and ClaimEventsRepository. Test cases: (1) happy-path export from approved state, (2) exception thrown when claim is in pending state, (3) exception thrown when claim is in rejected state, (4) CLAIM_ALREADY_EXPORTED exception on double-export, (5) actor ID correctly sourced from auth context not payload, (6) atomic failure leaves claim in approved state. All tests must pass with 100% branch coverage on markAsExported().
The ThresholdEvaluationService is described as shared Dart logic used both client-side and in the Edge Function. Supabase Edge Functions run Deno/TypeScript, not Dart, meaning the threshold logic must be maintained in two languages and can diverge, causing the server to reject legitimate client submissions.
Mitigation & Contingency
Mitigation: Implement the threshold logic as a single TypeScript module in the Edge Function and call it via a thin Dart HTTP client wrapper for client-side preview feedback only. The server is always authoritative; the client version is purely for UX (showing the user whether their claim will auto-approve before they submit).
Contingency: If dual-language maintenance is unavoidable, create a shared golden test file (JSON fixtures with inputs and expected outputs) that is run against both implementations in CI to detect divergence immediately.
A peer mentor could double-tap the submit button or a network retry could trigger a duplicate submission, causing the ApprovalWorkflowService to attempt two concurrent state transitions from draft→submitted for the same claim, potentially resulting in two audit events or conflicting statuses.
Mitigation & Contingency
Mitigation: Implement idempotency in the ApprovalWorkflowService using a database-level unique constraint on (claim_id, from_status, to_status) per transition, combined with a UI-level submission lock (disable button after first tap until response returns).
Contingency: Add a deduplication check at the start of every state transition method that returns the existing state if an identical transition is already in progress or completed within the last 10 seconds.
Claims with multiple expense lines (e.g., mileage + parking) must have their combined total evaluated against the threshold. If individual lines are added asynchronously or the evaluation runs before all lines are persisted, the auto-approval decision may be computed on an incomplete set of expense lines.
Mitigation & Contingency
Mitigation: The Edge Function always fetches all expense lines from the database (not from the client payload) before computing the threshold decision. Define a clear claim submission contract that requires all expense lines to be persisted before the submit action is called.
Contingency: Add a validation step in ApprovalWorkflowService that counts expected vs. persisted expense lines before allowing the transition, returning a validation error if lines are missing.