Each lab contains README, lab.toml, rubric, starter (with NotImplementedError stubs),
solution (reference implementation), and tests. Labs cover:
- Junior: FastAPI basics, validation, Pydantic v2, response_model, error handling,
  DI, async SQLAlchemy, auth (JWT/OAuth2), file uploads, WebSocket, background tasks
- Middle: Celery, caching, middleware, async patterns, performance, security,
  versioning, documentation, Docker, CI/CD, microservices
- Senior: event-driven, GraphQL, serverless, best practices
- Gates: junior_gate, middle_gate, senior_gate (comprehensive skill checks)

Test infrastructure: conftest.py with --lab-variant=starter|solution switch,
32 labs in testpaths, uv.lock pinned. 373 solution tests pass, 0 warnings.