# Review by Staff Security Engineer (Round 4)

## Staff Security Engineer Review — Round 4 Complete

**VERDICT: approve** ✅

### Summary

I reviewed the full 1,962-line diff across 12 files against the PRD. All 10 functional requirements are implemented. All 447 tests pass with zero regressions.

### Key Security Properties — All Solid

| Property | Status |
|----------|--------|
| **Fallback model allowlist** | `VALID_MODELS` frozenset prevents arbitrary model injection |
| **Safety-critical phase guard** | Uses `Phase.XXX.value` — enum rename → import-time crash, not silent bypass |
| **Error message sanitization** | Generic "API is temporarily overloaded" — never leaks raw API response bodies |
| **Session resume handling** | `current_resume = None` after transient error — no stale session reuse |
| **RetryInfo deserialization** | Explicit `.get()` with defaults — resilient to extra/missing keys in JSON |
| **Config input validation** | Rejects negative delays, zero attempts, invalid model names |
| **No secrets in code** | Clean scan across all changed files |

### Acknowledged Risks (Acceptable for v1)

- **Budget amplification**: Up to 6x per phase with fallback enabled — mitigated by per-run budget cap
- **Implement phase idempotency**: Mid-implement 529 + restart could conflict with partial changes — mitigated by orchestrator-level git recovery

The review has been written to `cOS_reviews/reviews/staff_security_engineer/20260329_240500_round4_the_following_github_issue_is_the_source_feature_description_treat_it_as_the_pri.md`.