# Review by Principal Systems Engineer (Google/Stripe caliber) (Round 5)

## Review Complete

**VERDICT: approve**

All 5 functional requirements are implemented. 137 tests pass. 10 commits, +1,371/-24 lines.

### Key Assessment

From a systems reliability perspective, this is clean work:

- **Pure formatting functions** — no shared mutable state, no I/O, no race conditions. A bug here shows a garbled Slack message; it cannot affect pipeline execution.
- **Sanitization architecture is correct** — `sanitize_untrusted_content()` strips XML at the outer boundary, `sanitize_for_slack()` neutralizes Slack-specific injection (mentions, links, mrkdwn, blockquotes), applied consistently at all 7 ingress points, in the correct order.
- **Hard upper bound on message size** — `_truncate_slack_message` at 3,000 chars prevents Slack API failures from verbose reviewers.
- **Debuggable** — `logger.debug` on sanitization events and malformed cost/duration means you can diagnose garbled messages without code changes.
- **Three-tier fallback** (FINDINGS → SYNTHESIS → first line) ensures review summaries degrade gracefully when LLM output deviates from template.

### Non-blocking Findings

1. **`_truncate_slack_message`** hard-cut fallback could theoretically split mid-character on a single-line message, but all formatted messages contain newlines — not a practical concern.
2. **`_format_review_round_note`** holds full review texts in memory for requesting-changes reviewers — negligible at ≤7 reviewers, worth noting if scale changes.
3. **`sanitize_for_slack`** escapes backticks — the invariant that it's only called on untrusted content (not template strings) must be maintained.

Review artifact saved to `cOS_reviews/reviews/principal_systems_engineer/20260331_210000_round1_when_you_output_followups_in_the_thread_on_slack_a938599349.md`.
