The key-needs-a-workspace error arrived as 'must include the anthropic-workspace-id header' and was reported as a bare 500 instead of 503 assistant_misconfigured naming the variable. Match the header name, not the sentence around it. Co-Authored-By: Claude Opus 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01KGcjxF1cNLcuwc3DAPcnfj