Session hangs silently after successful tool_call_output (no final_answer/task_complete) #13475

I hit a reproducible hang in Codex where a turn stops producing output after a successful tool call.

What happened:

1. Assistant said it was about to write tasks.md.
2. It issued exec_command with a heredoc to write:
   openspec/changes/phase-2-backend-conversation-orchestrator/tasks.md
3. The tool call returned successfully:
   function_call_output for call_NIdhkoLSQsLfgiP3cbhBtLe8
   Process exited with code 0
4. After that, the turn produced no more events:
   • no agent_message
   • no final_answer
   • no task_complete

Stall window:

• Last successful event: 2026-03-04T13:57:51.468Z
• Next activity only when I manually interrupted: 2026-03-04T14:12:00.856Z
• Silent stall duration: ~14 minutes

Important notes:

• This is NOT caused by my manual interrupt. The interrupt happened much later, after the stall.
• The target file was fully written and valid.
• I could continue development afterward; artifacts were intact.
• No crash report for codex/node in DiagnosticReports at that time.
• codex-tui.log shows no explicit parse/schema/protocol error for this thread around the stall point.

Expected behavior:
After a successful function_call_output, the turn should always either:

• continue with assistant output, or
• terminate with an explicit error/completion event.

Actual behavior:
Turn enters a silent hang state with no output and no completion signal.

Please investigate possible runner/state-machine deadlock or dropped stream event in the post-tool-output finalize path.