Stop hook error 'Failed with non-blocking status code: No stderr output' prevents completion event from being emitted

[gnguralnick]

Summary

When a working agent finishes its task, the Claude Code stop hook fires but fails with:

Stop hook error: Failed with non-blocking status code: No stderr output

As a result, no mng/agent_states completion event is emitted to the parent mind, so the mind never learns the agent finished.

Steps to reproduce

1. Create a working agent via mng create <name> worker --message-file ...
2. Agent completes its task successfully (writes output files, prints summary)
3. Observe stop hook error in mng capture <agent> output
4. Parent mind never receives a completion event for the agent

Expected behavior

Stop hook runs successfully → completion event emitted → parent mind receives mng/agent_states event with the agent's final state.

Actual behavior

Stop hook fails silently. Parent mind never notified. User had to manually inform the mind that the agent was done.

Environment

• Agent type: worker (claude-mind harness)
• Observed on: explore-slack-summarize agent (agent-3dc672424d774aa0b751dfb3b67514a9)
• The agent itself completed successfully — output files were written, final summary was printed
• Error appears at the very end of the agent's tmux output after "✻ Brewed for 4m 52s"