codex-exec: allow resume --last to read prompt #6717

[dkhokhlov]

Description

• codex exec --json resume --last "" bailed out because clap treated the prompt as SESSION_ID. I removed the conflicts_with flag and reinterpret that positional as a prompt when
  --last is set, so the flow now keeps working in JSON mode. (codex-rs/exec/src/cli.rs:84-104, codex-rs/exec/src/lib.rs:75-130)
• Added a regression test that exercises resume --last in JSON mode to ensure the prompt is accepted and the rollout file is updated. (codex-rs/exec/tests/suite/resume.rs:126-178)

Testing

• just fmt
• cargo test -p codex-exec
• just fix -p codex-exec
• cargo test -p codex-exec

#6717

[github-actions]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[dkhokhlov]

I have read the CLA Document and I hereby sign the CLA

[dkhokhlov]

Dropping conflicts_with = "session_id" was safe here:

• The only time clap used that constraint was to reject resume --last when was parsed as SESSION_ID. We now re-interpret that positional as the prompt whenever --last is set.

• Users can still run resume <SESSION_ID> without --last; the parser still sets session_id and leaves last false, so nothing changes for that flow.

• If someone deliberately provides both an ID and --last, we prefer the session_id path because we only treat the positional as a prompt when last is true and no explicit prompt was supplied. So accidental conflicts disappear, and intentional resume --last -- session-id (if someone tried) still resolves consistently.

Clap doesn’t need the explicit conflicts_with once the parser logic distinguishes the cases.

[etraut-openai]

Thanks for the contribution. Please take a look at the codex code review above.

[dkhokhlov]

@etraut-openai any action on my side? that code comment was from me.

[etraut-openai]

@codex review

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Restore --last/session_id conflict

Removing conflicts_with = "session_id" means clap will now happily parse codex exec resume <SESSION_ID> --last. With the new prompt fallback we even reinterpret that <SESSION_ID> as the prompt, but resolve_resume_path still treats args.last as authoritative and ignores the provided id. The net result is that this command (which used to error) silently resumes the most recent conversation instead of the explicit session the user asked for, and sends the session id string as the first prompt. That is a regression in CLI safety—users/scripts that accidentally pass both options now touch the wrong session. We need to keep the conflict (or otherwise reject the combination) while fixing the JSON-mode prompt parsing.

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[nornagon-openai]

This is correct, but I'm not sure how to express this more cleanly with clap.