[BUG] duplicate assistant messages

What version of Codex is running?

codex-cli 0.23.0 (but on HEAD it happens, as well)

Which model were you using?

gpt-5

What platform is your computer?

Darwin 24.6.0 arm64 arm

What steps can reproduce the bug?

Send two messages in a row; if you check the request body in the second request, it will include a duplicate of the assistant's message from the first request.

What is the expected behavior?

It should only include one (not duplicate) assistant message.

What do you see instead?

There are two duplicate assistant responses.

If you ask the model, it will confirm the suspicion (it is reaching the model, unfortunately).

Additional information

Lots of wasted tokens :)