Add a run-race spec case where runHooks.begin rejects with a plain Error (not RunAlreadyActiveError): assert stream() does not 409, logs the legacy fallback, persists the user message, and streams untracked on the socket signal (effectiveSignal = signal, runId undefined). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>