Responses API replay can fail on orphan reasoning item after interrupted turn #17161

Summary

Codex can resend an orphan reasoning item when replaying history after an interrupted turn, which causes the Responses API request to fail instead of self-healing.

The concrete API error is:

{
  "error": {
    "message": "Item rs_... of type reasoning was provided without its required following item.",
    "type": "invalid_request_error",
    "param": "input"
  }
}

Problem shape

A bad persisted/replayed sequence looks like:

1. trailing reasoning item
2. synthetic <turn_aborted> user marker
3. next real user message

In that shape, the replayed request contains a reasoning item without the model-generated item that originally followed it, and the Responses API rejects the request.

Expected behavior

Codex should detect this narrow invalid-request case, repair the replayed input/history by dropping only the orphan reasoning item, and retry once.

Proposed fix

I implemented a working patch on my fork here:

• Commit: f3b9e8344c58b50bb0637f7ecdfcb9230cb27e82
• URL: jgrantJump@f3b9e83

The patch does two things:

• normalizes replayed history so incomplete reasoning items are removed while preserving <turn_aborted>
• retries once for the exact missing-following-item error on both HTTP and websocket Responses transports

Validation on the patch

• just fmt
• just fix -p codex-core
• cargo test -p codex-core missing_reasoning -- --nocapture

I couldn’t upstream the PR directly because this repository limits PR creation to collaborators, but the fork commit above should be enough to review or cherry-pick.