Implement signed URL and API push confirmation response handling
epic-accounting-system-export-orchestration-task-008 — Based on the ExportResult type returned by AccountingExporterService, implement the two response branches in the Edge Function: (1) if output is a file, generate a time-limited (15-minute) Supabase Storage signed URL and return it to the client; (2) if output is an API push to Xledger or Dynamics, return a structured confirmation payload with the external transaction reference. Handle error cases with appropriate HTTP status codes and JSON error bodies.
Acceptance Criteria
Technical Requirements
Execution Context
Tier 6 - 158 tasks
Can start after Tier 5 completes
Implementation Notes
Use `supabaseServiceClient.storage.from('accounting-exports').createSignedUrl(filePath, 900)` for signed URL generation. The 900-second value should be defined as a named constant (SIGNED_URL_EXPIRY_SECONDS) in a config file — do not hardcode inline. The ExportResponse discriminated union should use TypeScript's `type` field as the discriminant for clean narrowing: `if (result.outputType === 'FILE') { ... } else if (result.outputType === 'API_PUSH') { ...
}`. For the expiresAt field, compute it as `new Date(Date.now() + 900_000).toISOString()` at response time. Avoid loading the file contents — the client downloads directly from the signed URL. Consider adding a download_expires_at field to the export run record so the audit trail shows when access expires.
Testing Requirements
Unit tests for the response branch logic using Deno.test with mocked Supabase Storage client. Test cases: (1) FILE branch — mock createSignedUrl success, assert response shape and 200 status; (2) FILE branch — mock createSignedUrl failure, assert 500 response; (3) FILE branch — mock storage 404, assert 404 response; (4) API_PUSH branch — assert confirmation payload shape and 200 status; (5) NO_DATA branch — assert 204 with {type: 'no_data'}; (6) assert signed URL expiry is exactly 900 seconds in all FILE branch calls. Integration tests in task-009 will cover the full end-to-end path including real Storage interactions.
The Edge Function may exceed Supabase's execution time limit (default 150 seconds, but effectively constrained by the 10-second client SLA) when processing large batches of claims with complex chart-of-accounts mapping, causing the export to fail after partial processing.
Mitigation & Contingency
Mitigation: Implement the export pipeline with early termination on timeout and an in-progress export run status. Add a benchmark test in CI that runs the full pipeline against 500 claims and fails if it exceeds 8 seconds. Optimize the approved claims query with indexes on status, org_id, and date fields.
Contingency: If performance targets cannot be met synchronously, convert the Edge Function to an async job pattern: the function queues the export and returns a job ID immediately; the client polls a status endpoint and downloads the file when ready. This requires a job queue table and a polling UI state.
Supabase Vault access from the Edge Function may require specific service role key configuration that differs between staging and production environments, causing credential retrieval to fail silently and producing export runs that appear successful but have no valid accounting system target.
Mitigation & Contingency
Mitigation: Test Vault read access in the Edge Function in staging before implementing any business logic. Add an explicit credential validation step at Edge Function startup that fails fast with a clear error if Vault is unreachable or the secret is missing.
Contingency: If Vault access fails in production, fall back to environment variable-based credentials temporarily (never returned to client) while the Vault configuration is corrected. Alert on-call via a monitoring rule that fires if credential retrieval fails.
AccountingExporter Service may become tightly coupled to specific exporter implementations if the factory pattern is not implemented cleanly, making it difficult to add a third exporter in the future without modifying the orchestrator.
Mitigation & Contingency
Mitigation: Define an AccountingExporter abstract class with a strict interface contract before implementing any concrete class. Use a registry pattern (Map<orgType, AccountingExporter>) in the factory rather than conditionals. Code review should verify no concrete class is imported directly in the orchestrator.
Contingency: If tight coupling is discovered after implementation, refactor the factory before the Edge Function epic ships so the interface is stable before any external callers are wired in.