pg_repo now preserves PostgreSQL constraint metadata and original error chains without assigning BusinessCode or HTTP statuses. Services own business classification and final logging of returned dependency errors; the library retains debug diagnostics for those errors and error-level logs for its own internal failures. Includes rollback error preservation, wrapping fixes, documentation of the logging migration contract, and regression tests for query, iteration and commit failures, transaction ownership and no write retries. Validation: go test -race ./... and go vet ./... passed. Live PostgreSQL was unavailable; regression tests use database/sql with a controlled driver. Service dependency updates and GraphQL response mapping remain separate work for IN-784.