REST API adapter dispatch router in Edge Function

Structure the router as a single handler function: serve(async (req) => { ... }) using Supabase's serve helper. Use a plain object as the AdapterRegistry (a Map) populated at module load time — this avoids dynamic require/import overhead per request. Define an IntegrationAdapter interface: { execute(config: IntegrationConfig, mappedPayload: object): Promise }.

Each adapter (XledgerAdapter, DynamicsAdapter, etc.) implements this interface and is responsible for its own HTTP calls to the external system. The FieldMappingResolver should query the field_mappings table in Supabase using the service role client and apply transformations — memoize the mapping lookup per integrationId within the invocation using a local Map. Wrap the entire handler body in a try/catch to guarantee that unhandled errors always return a valid JSON response rather than a Deno runtime error page. Use AbortSignal.timeout(30_000) for all external adapter HTTP calls to enforce the per-adapter timeout.

Write Deno unit tests covering: (1) valid request routes to the correct adapter and returns 200 with result; (2) missing required field returns 400; (3) unknown integrationTypeId returns 422; (4) CredentialNotFoundError from adapter returns 503; (5) generic adapter error returns 502 with sanitised message; (6) field mapping resolver is called with the correct integrationId and payload before the adapter; (7) adapter receives the resolved (transformed) payload, not the raw one. Mock AdapterRegistry, FieldMappingResolver, and CredentialProvider — do not make real external API calls in unit tests. Additionally write one integration test (integration_test/) that deploys the function to a local Supabase instance and sends a real POST request with a stub adapter registered for 'test-type'.