- Fix MagicMock poisoning: add target_column=None to _make_mock_job/mock_job fixtures (3 files) - Add FetchModelsRequest Pydantic model for type-safe fetch-models endpoint - logger.warning→logger.error for fetch_models 502 path - Early validation: require api_key or provider_id in fetch-models - 50 tests pass, 0 failures (test_clickhouse_insert_integration, test_orchestrator, test_preview)