Node contract data and validation for Pureflow.
Fragment: contract-data-boundary
This crate keeps the contract layer thin: it owns typed contract metadata and validation against validated workflow topology plus existing capability descriptors. It does not add a second capability model, a parser, or a runtime.
Fragment: contract-validation-boundary
Validation is intentionally staged. Workflow structure is still owned by
pureflow-workflow, capability descriptors remain in pureflow-core, and
this crate only verifies that the two line up with the contract metadata
supplied for inspection or execution planning.