Steered input can look like a standalone latest user request and drop unfinished task context

What variant of Codex are you using?

CLI 0.139.0

What issue are you seeing?

When I send a steer message while Codex is already working, Codex can treat the steer as the new main task and lose track of the unfinished task it was previously executing.

Minimal example:

1. User asks Codex to do task B:

``text
Inspect the repo, make the requested fix, run tests, and report the result.
``

1. Codex starts task B and runs tools.

1. Before task B finishes, user sends a steer message A:

``text
Also make sure the final answer is in Chinese.
``

1. Codex sends the next model request after receiving the steer.

Observed result: Codex may continue with only A in mind, or answer A, but fail to resume the unfinished parts of B.

Expected result: Codex should incorporate A without losing B. If A does not replace B, Codex should continue or resume B after applying A.

Suspected cause

Same-turn steer input is accepted as active-turn pending input and later drained into the next model request as user input. That preserves the raw message, but the model-facing history is too close to:

user: task B
assistant/tool: work in progress
user: steer A

The last message looks like a standalone latest user request. It does not clearly say that A arrived while Codex was already working on B, or that B may still be unfinished.

Suggested direction

When drained steer input is added to the next model request, it should carry explicit mid-turn follow-up semantics instead of looking like a bare standalone user message.

One possible shape:

<user_followup>
The user sent this while Codex was already working:
A

Apply this follow-up without dropping the current unfinished task unless it explicitly replaces that task.
</user_followup>

This should preserve the current cache-friendly behavior of appending new input near the next model-request boundary, without rewriting earlier history.

Areas to investigate in the existing code:

• active-turn steer input acceptance in Session::steer_input;
• pending input ownership and drain behavior in InputQueue;
• the path that records drained TurnInput::UserInput before the next model request;
• pending-input / steer tests that can assert the next model request contains wrapped follow-up text exactly once.