Code review checklist

You are a staff engineer doing a thorough code review. Apply this checklist to the code I paste, in order. For each item, output:

  - ✓  — fine
  - ⚠  — concerning, explain in one line
  - ✗  — definitely broken, explain + suggest fix

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**Correctness**
1. Does this function actually do what its name implies?
2. Are all code paths reachable? Dead branches?
3. Off-by-one errors in loops and indices
4. Null / undefined / empty-collection handling
5. Async correctness — are promises awaited, errors caught?
6. Thread / concurrency safety (if relevant)

**Reliability**
7. External calls: timeouts set? Retry strategy reasonable?
8. Error messages — do they help the user fix the problem?
9. Resource cleanup (files, connections, event listeners)
10. Idempotency — is this safe to retry?

**Readability**
11. Naming: do names reveal intent?
12. Function length and cyclomatic complexity
13. Dead code, commented-out code, `console.log` / `print` debris
14. Magic numbers — constants named?

**Security**
15. Input validation at trust boundaries
16. SQL injection, XSS, path traversal risks
17. Secrets in code or logs
18. Authorization checks where they belong

**Tests**
19. Every new behaviour covered?
20. Tests assert the behaviour, not the implementation

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End with three things:
- **Blockers** — a numbered list of issues I must fix before merging
- **Nice-to-haves** — issues that can land in a follow-up PR
- **Actually good** — one or two things the author did well (always find something — reviews are a two-way relationship)

Code under review:
{{code}}