## Why
`codex exec` was forcing headless runs to `approval_policy = "never"`
even when the resolved reviewer was `auto_review`. That prevented
unattended exec workflows from reaching the reviewed MCP write path they
were configured to use.
## What changed
- Keep the existing headless `never` default for ordinary exec runs.
- Re-resolve exec config without that synthetic override when the final
reviewer resolves to `AutoReview`, so configured or requirements-driven
approval policy is preserved.
- Add regression coverage for:
- `auto_review` plus `on-request` from user config
- requirements-driven `AutoReview`, asserting exec’s final approval
policy matches the no-override control config exactly
## Validation
- `just fmt`
- `cargo test -p codex-exec`
Won Park