FastAPI best practices and conventions for clean, modern API development.

• Use Annotated for all parameter and dependency declarations to maintain type safety, reusability, and compatibility with other contexts
• Declare return types or response models on path operations to enable automatic validation, filtering, serialization, and OpenAPI documentation
• Use async def only when calling async code with await; default to regular def for blocking operations to avoid event loop blocking
• Apply router-level configuration (prefix, tags, dependencies) on the APIRouter itself rather than in include_router() calls
• Avoid deprecated patterns like Ellipsis (...) for required fields, RootModel, and custom JSON response classes; rely on Pydantic's Rust-based serialization for performance