# Review by Staff Security Engineer (Round 4)

## Security Review Complete — Round 4

**VERDICT: approve** ✅

### Summary

All three critical findings from my round 3 review have been resolved:

1. **ANSI escape regex gaps → FIXED.** The sanitizer now strips CSI, OSC (`\x1b]...\x07`), DCS (`\x1bP...\x07`), and single-char escape sequences. This closes terminal window retitling and clipboard write attack vectors.

2. **Bare `\r` carriage return → FIXED.** CRLF is normalized to LF, bare `\r` is stripped. The content-overwrite attack (`"safe text\rmalicious"`) is neutralized with test coverage.

3. **User message sanitization → FIXED.** `append_user_message()` now passes input through `sanitize_display_text()`.

### Key Security Strengths
- **Complete output sanitization pipeline**: Every path from agent/tool output to terminal display passes through `sanitize_display_text()`
- **Thread-safe by construction**: Frozen dataclasses for queue messages eliminate mutation races
- **Clean dependency isolation**: `textual` and `janus` are optional, with actionable error messages
- **Zero regressions**: All 1,695 existing tests pass, plus 147 new tests

### Remaining Low-Severity Items (acceptable for v1)
- Unbounded `_tool_json` buffer (requires compromised SDK stream)
- No composer input length limit (user is local)
- Rich Markdown link rendering (not clickable, informational only)

Review artifact written to `cOS_reviews/reviews/staff_security_engineer/20260323_200000_round4_give_me_fucking_awesome_ux_that_is_a_fucking_amazing_experience_and_it_gets_peop.md`.