Restore support for the experimental_resume config option in codex proto

What feature would you like to see?

• Summary: Bring back the documented experimental_resume config flag so that codex proto can resume a session from a JSONL log. Recent builds ignore this flag entirely, forcing every proto run to start fresh

even when a resume file is supplied.

• Motivation / use cases: When debugging complicated multi-turn interactions or sharing reproducible repro logs, being able to restart proto against an existing rollout is invaluable. This worked in earlier

releases and is still described in docs/config.md (docs/config.md:653), but the plumbing was removed when the newer codex resume flow landed.

• Current behaviour: On current main, adding either

--config experimental_resume="/path/to/session.jsonl" or a matching entry in ~/.codex/config.toml has no effect. The CLI always reports resume_path: None (see logs in codex-rs/tui/tests/fixtures/binary-size-
log.jsonl) and starts a brand new conversation.

• Expected behaviour: When experimental_resume points at a valid JSONL rollout generated by proto, the CLI should load those turns, send the initial history to the backend, and append new turns to the same file—

mirroring the behaviour seen in earlier releases.

• Proposed direction: Restore and polish the experimental_resume code path so resolve_resume_path (and the TUI entry point) fall back to config.experimental_resume whenever neither --last nor session_id is

supplied. This is blocking existing workflows; removing the knob isn’t viable. I’d love to see this reinstated and graduated from “experimental” to a documented, supported feature in an upcoming release.

Are you interested in implementing this feature?

_No response_

Additional information

_No response_