Audit already-implemented Data warehouse import sources for endpoints, schemas, and tables the vendor's API offers but we never wired up. Use when asked whether a source is missing endpoints, to find new endpoints a vendor has added since a source was built, to refresh COVERAGE_GAPS.md, to prioritize which source to deepen next, or to check coverage before an integration review. Covers dumping our real endpoint inventory credential-free, ranking sources by production adoption, diffing against vendor OpenAPI/GraphQL specs, and recording findings. Not for implementing a source (use implementing-warehouse-sources), adding a vendor API version (warehouse-source-new-version), or writing source docs (documenting-warehouse-sources).