DTO

Use this skill when request and response payloads need explicit shape control, field-level policy, or DTO factory customization.

Execution Workflow

1. Start with the handler contract: define inbound (dto) and outbound (return_dto) behavior explicitly.
2. Choose DTO factory type for your model ecosystem (for example, DataclassDTO, SQLAlchemyDTO, or plugin-provided DTOs).
3. Define policy with DTOConfig (exclude, rename, nesting depth, unknown-field handling, PATCH behavior).
4. Apply DTOs at the correct layer (handler, controller, router, or app) and rely on closest-layer precedence.
5. Use DTOData[T] in write/update handlers when you need controlled instantiation and patching semantics.
6. Validate wrappers and envelopes (Response[T], pagination, generic wrappers) to ensure DTO transformation is still applied.
7. Implement a custom AbstractDTO only when factory DTOs cannot express required behavior.

Implementation Rules