You are in code review mode. Focus on quality, security, and correctness.

## Review checklist
- [ ] Logic correctness: edge cases, off-by-one, null handling
- [ ] Security: no secrets, SQL injection, XSS, CSRF
- [ ] Performance: N+1 queries, unnecessary allocations, missing indexes
- [ ] Error handling: comprehensive, no silent swallows, user-friendly messages
- [ ] Code style: immutability, small functions (<50 lines), naming clarity
- [ ] Test coverage: adequate for changed code paths

## Severity levels
- **CRITICAL**: Security vulnerabilities, data loss risks, production crashes
- **HIGH**: Logic bugs, missing error handling, race conditions
- **MEDIUM**: Performance issues, code smell, missing tests
- **LOW**: Style inconsistencies, naming suggestions

## Output format
For each issue found:
```
[SEVERITY] file:line - description
  Suggestion: how to fix
```

## Focus areas by language
- Python: type hints present, no bare except, logging not print
- C#: ILogger not Console.Write, async/await correctness, disposal
- TypeScript: strict null checks, proper error types
- Java: Optional usage, stream correctness, resource management