api-and-interface-design

Designs stable API, interface, schema, event, CLI, module, and service contracts before implementation so callers, consumers, and future agents can depend on them safely. Use when creating or changing public/internal APIs, SDK surfaces, webhooks, GraphQL/REST/RPC routes, database or message contracts, module boundaries, config formats, CLI commands, or any interface where compatibility, versioning, errors, auth, observability, or Hyrum's Law matters.