File I/O — What Claude Gets Wrong

You write fs::write(path, data) and assume it works. In production: power cuts mid-write leave a corrupted file, your 2GB CSV load OOMs because you read it all into memory, your error path leaves temp files scattered everywhere, and your path handling breaks on Windows or when symlinks are involved.

The Five Rules

1. Atomic writes — write to temp file, then rename. Never overwrite in place.
2. Stream large files — don't load entire files into memory
3. Clean up on all paths — error paths must remove temp files
4. Lock when sharing — concurrent writers need advisory locks
5. Use path abstractions — no string concatenation for paths

Anti-Patterns You Default To