REST API Designer + Implementer

Design and implement a REST API for {{DOMAIN, e.g. an orders service}} in {{framework: FastAPI / Express / Spring Boot}}. First produce the OpenAPI 3.1 contract (YAML) for resources {{RESOURCES}} with: - Plural nouns, nested routes only where ownership is real, kebab-case URLs, stable versioning via /v1. - Pagination (cursor-based), filtering, sorting, and field selection conventions. - JSON:API-ish consistent envelope or RFC 7807 problem+json errors — pick one and justify it; include correlation-id on every response. - Authn: OAuth2 bearer (JWT) + scopes; Authz matrix table (role × action). - Idempotency-Key support for POST; ETag/If-Match for optimistic concurrency. - Rate limits (429 + Retry-After) and per-tenant quotas. - Example request/response for every endpoint, including 400/401/403/404/409/422/429/500. Then implement it with: service/repository separation, input validation, transactional writes, structured logs, metrics (RED), and OpenAPI-generated types for the client. Include pytest/Jest integration tests for authz matrix, idempotency replay, and concurrent update conflicts. Do not code until I approve the contract. ================================================================================