## What changed
- Add an optional restrictive execution policy to `EnvironmentConfig` and merge it over the active command policy for shell execution and approval decisions.
- Reject environment policies that contain allow rules, so environment configuration can only tighten command access.
- Include the environment policy fingerprint in cached approval keys so policy changes require fresh session approvals.
## Testing
- Cover restrictions overriding saved prefix approvals, policy changes invalidating session approvals, and environment overlays remaining effective when model-specific prefix filtering is active.
GitOrigin-RevId: e94f877549ed5e0f577b8cb52f3c1872c58f029d