Middleware Pipeline (Chain of Responsibility Pattern)

Every web framework runs each request through a pipeline of middleware: authenticate, rate-limit, then dispatch to the app. That pipeline is the Chain of Responsibility pattern. You will build a handler base that passes requests down a chain, add auth and rate-limit stages that can short-circuit the pipeline, write a terminal app handler, and finish with a builder that wires any list of handlers into a chain — the exact machinery behind Express and Django middleware.