The registry fixture sent response headers before reading the upstream body, then always wrote a 500 on error. A body failure hit ERR_HTTP_HEADERS_SENT, which hid the real error and crashed the verifier with its helper still running. The fixture now reads the body first, destroys a response that already started, and the verifier rethrows the first fixture error. Refs #6038. 🤖 Generated with Claude Code (Sonnet 5.5) 🦊 Co-authored-by: Claude Sonnet 5.5 <noreply@anthropic.com>