## Summary
This is the minimal client-side follow-up for the Codex Auto Review
model slug rollout. It updates the guardian reviewer preferred model
from `gpt-5.4` to `codex-auto-review`, so the client can rely on the
backend catalog + Statsig mapping instead of hardcoding the GPT-5.4
slug.
Context:
https://openai.slack.com/archives/C0AF9328RL0/p1775777479388369?thread_ts=1775773094.071629&cid=C0AF9328RL0
## Testing
- `cargo fmt --package codex-core --check`
- `cargo test -p codex-core guardian::`
- `bazel test --experimental_remote_downloader= --test_output=errors
//codex-rs/core:core-unit-tests --test_arg=guardian`
