Describe SQLAlchemy setup in FastAPI from database config to endpoint

Tests practical knowledge of FastAPI dependency injection and SQLAlchemy session lifecycle. A strong answer lists four components in order: a pooled database engine configured once at startup, declarative models mapping to PostgreSQL tables, a yield-based session dependency that handles rollback on error and always closes, and an endpoint that declares the session as a dependency to query and return users. Red flags include creating an engine per request, sharing one global session for all requests, or leaking connections by skipping cleanup.