Agent Skills: api-design

Load PROACTIVELY when task involves building or modifying API endpoints. Use when user says \"build an API\", \"add an endpoint\", \"create a REST route\", \"set up GraphQL\", or \"add tRPC procedures\". Covers route design and file organization, request validation with Zod, response formatting, error handling patterns, middleware composition, authentication guards, rate limiting, pagination, and API documentation generation.