Codex Desktop hangs before turn start when a Skill and certain ChatGPT conversation references are attached

Summary

On macOS, Codex Desktop can hang indefinitely before a turn is created when a local user Skill and a specific ChatGPT conversation reference are attached to the same prompt. The entire app becomes unresponsive and requires force quit.

This reproduces deterministically for one referenced conversation, while other referenced conversations work with the same Skill and environment.

Related reports: #32342 and #33278. This report adds controlled comparison evidence that may help narrow the same failure path.

Environment

• Codex Desktop: 26.721.41059 (build 5848)
• Bundled Codex CLI: 0.146.0-alpha.3.1
• Platform: macOS

Steps to reproduce

1. Open a local Codex task.
2. Attach a local user Skill.
3. Attach ChatGPT conversation reference A.
4. Send a short prompt asking Codex to process the referenced conversation.
5. The composer remains in a running state indefinitely, and the app cannot recover without force quitting.

Control tests

• The same Skill with ChatGPT conversation reference B starts normally.
• Conversation reference A reproduces the hang with both the current and a previous complete release of the Skill.
• The first-party read_thread tool can read conversation A successfully when called directly without attaching the conversation reference in the composer.
• Larger referenced conversations have completed successfully, so serialized size alone is not sufficient to explain the failure.

Diagnostic evidence

In a controlled reproduction:

• Turn-start configuration resolved successfully.
• No turn/start request was emitted for approximately 199 seconds.
• The app was then force-quit.
• The resulting EPIPE appeared only during shutdown.
• The failed prompt was not persisted in the Codex task history.

No raw logs, session transcripts, conversation contents, local paths, names, IDs, or attachments are included in this report.

Expected behavior

Codex should either:

• create the turn and process the references, or
• fail with a recoverable, user-visible error.

A referenced conversation should not leave the entire desktop app stuck before turn creation.

Actual behavior

The app hangs indefinitely during client-side preflight or reference handling and requires force quit.

Additional notes

The evidence points to the Desktop client path that hydrates or serializes certain ChatGPT conversation references before turn creation. The model and Skill workflow do not appear to begin executing.