Stop hook should include recent messages to enable external memory systems

[Liewzheng]

Summary

External memory systems (e.g. Mimir) need to persist the user/assistant exchange at the end of a turn. The current Stop hook only exposes last_assistant_message and a transcript_path, which forces integrations to parse the Codex JSONL transcript themselves.

Request

Include an inline messages array in the Stop and SubagentStop hook payloads, containing the recent user/assistant exchange. This would make Codex easier to integrate with external memory systems without requiring them to parse transcript_path.

This request mirrors the interface introduced in MoonshotAI/kimi-code#1299.

Proposed schema

{
  "messages": [
    { "role": "user", "content": "..." },
    { "role": "assistant", "content": "..." }
  ]
}

messages should be optional to preserve backward compatibility.

Reference implementation

I have implemented this on a fork at Liewzheng/codex in the branch mimir-stop-messages (see Liewzheng/codex@main...mimir-stop-messages). The changes include:

• Added StopMessage { role, content } to codex-rs/hooks/src/schema.rs.
• Added an optional messages field to StopCommandInput and SubagentStopCommandInput.
• Populated messages from the last user/assistant entries in the JSONL transcript when the caller does not provide them inline.
• Updated codex-rs/core/src/hook_runtime.rs to thread messages into the Stop request.
• Regenerated schema fixtures for stop.command.input and subagent-stop.command.input.
• Added unit tests for the transcript fallback.

I'd be happy to open a PR, but I see this repository currently restricts pull requests to collaborators. Please let me know if you'd like me to provide the patch in another format or if there's a process for external contributors.

[Liewzheng]

Update: pushed a small fix to the reference branch so that SubagentStop falls back to agent_transcript_path (the subagent transcript) when extracting recent messages, instead of the parent thread transcript.

Branch: Liewzheng/codex@main...mimir-stop-messages

I cannot run cargo check locally right now because crates.io is timing out from this environment, so the patch has not been machine-verified here. It will rely on CI once a maintainer can open a PR from the branch.

[Liewzheng]

Verification update (with proxy):

• cargo check -p codex-hooks ✅
• cargo test -p codex-hooks ✅ (121 passed)
• cargo check -p codex-core ✅

Also regenerated the schema fixtures with cargo run -p codex-hooks --bin write_hooks_schema_fixtures so the generated schemas and fixtures stay in sync.

Latest branch: Liewzheng/codex@main...mimir-stop-messages