Codex 0.160.0 resumes queued messages after reconnect: Sume key rule

Codex 0.160.0 does not remove the need for an idempotency_key on Sume paid calls. Its changelog entry for October 1-2, 2026 says unsent queued messages resume after reconnection once uncertain submissions resolve, avoiding duplicates. That protects the message queue in the client. A tool call that already left the machine and reached Sume is a separate event, and only a key on the call can make Sume treat a repeat as the same request.

What each layer covers

The Codex fact comes from the Codex changelog (read 2026-10-07). The Sume rules come from MCP tools and gates and Jobs and results.

A dropped connection

The table walks through a dropped connection in the middle of a paid call.

After a reconnect

After a reconnect, the safe sequence is:

• Do not make the paid call again from a fresh prompt. Look up the job first with jobs_list or jobs_status if you kept an id.
• If you have no id, repeat the call with the same idempotency_key. Sume returns the original job and reports a hit instead of billing twice.
• If the key matches but the body is different, expect a 409 conflict. Fix the body or use a new key on purpose.

Where the key should come from

Make the key from the business event, such as an order id plus a version, so that a fresh session produces the same key for the same intent. A random value made inside the model turn will differ after a resume.