## Review 006: Backend Models: Dead Code Removal

**Files reviewed:** src/backend/models.py
**Verdict:** accept

### Approvals

- Removing the unused `to_dict()` methods eliminates a point of confusion—readers no longer need to wonder which serialization path is canonical. The API layer correctly uses Pydantic response models; these methods were noise. Clean removal.
- Type annotations in SessionCreate and BreakCreate are correct: `start_time: datetime` and `end_time: datetime` reflect the post-validator types. The `@validator(..., pre=True)` decorator handles string-to-datetime conversion transparently. The contract (client sends ISO 8601 strings, backend works with datetime objects) is unambiguous and correctly encoded in types.
