Support User Changes to Codex's Internal Planning Without Interrupting Active Thread

What variant of Codex are you using?

CLI

What feature would you like to see?

Codex already has an internal checklist via update_plan, but users can only affect it indirectly by sending a normal message. During an active turn, this has resulted in interrupting the agent, redirecting the task, or being misunderstood as a request to write TODOs into files.

Proposal:

• /plan add <text> appends a pending item to the active checklist
• /plan clear clears the active checklist

Expected behavior:

• This should not interrupt the active turn.
• The agent should observe the updated checklist before its next reasoning step.
• The implementation should reuse the existing checklist/update_plan mechanic.

Result:

• Users will be able to more easily run multi-hour Codex sessions without premature stoppages.

Additional information

I'm happy to provide a PR if needed.