feature request: codex:reviewer subagent (review-mode counterpart to codex-rescue)

Problem

/codex:review and /codex:adversarial-review are great as standalone slash commands, but they can't be invoked from inside another plugin's command (slash commands don't compose). The only Codex artifact that can be dispatched programmatically — via the Agent tool — is the codex-rescue subagent, which is hard-coded to forward to codex-companion.mjs task ... (write-capable, not review-shaped).

This forces downstream plugins that want to chain a Codex review into a larger pipeline (e.g. a shipping pipeline that runs Codex review → human triage → CodeRabbit → merge) to either:

1. Use codex-rescue and trust prompt-level instructions to keep it read-only (semantically wrong — it's the rescue/fix agent), or
2. Reach into ~/.claude/plugins/cache/.../codex/scripts/codex-companion.mjs directly, which is fragile and breaks across version updates.

Proposed

Add a sibling subagent — codex-reviewer (and/or codex-adversarial-reviewer) — with the same thin-forwarding shape as codex-rescue, but invoking codex-companion.mjs review / adversarial-review instead of task. Hard-code review-only behavior (no --write, no --resume-last semantics needed). Returns Codex stdout verbatim.

This would let downstream plugins dispatch a Codex code review with one Agent call, matching the existing pattern for codex-rescue.

Use case

We're building thought-shower, a shipping pipeline plugin where Stage 3 runs Codex review on the open PR. Today it dispatches codex-rescue for this, which works but uses task-mode under the hood. A dedicated codex-reviewer agent would be a drop-in replacement with the right semantics.

Happy to send a PR if the maintainers are open to this.

Start by reading the existing codex-rescue subagent and the codex-companion.mjs entry point that it forwards to. Trace how Agent dispatches the current task-mode path, then add the review-shaped sibling using the proposed review or adversarial-review entry point. Done means downstream plugins can invoke it through Agent, receive Codex stdout verbatim, and cannot enable write or resume-last behavior.