API Contract

Treat an API change as a producer/consumer contract, not only a handler edit.

Trace request -> validation -> handler/service -> persistence -> response serialization -> client/generated types -> UI/consumer. Compare method/path, params/query/body, required/optional/nullability, enums, status/error shapes, pagination and date/number serialization.

Read workflow.md for compatibility analysis, source-of-truth selection, generated clients, error semantics and contract verification.