Test coverage for error detection and retry logic:
- extractStatusCode: 13 test cases for HTTP status code extraction
- isTransientRateLimitError: 17 test cases for rate limit detection
- isNotImplementedError: 14 test cases for 501 error detection
- isVMSpecificError: 16 test cases for VM-scoped errors
- calculateRateLimitBackoff: backoff timing verification
- isAuthError: 12 test cases for authentication errors
Coverage 35.5% → 37.3%