Explain Context Cancellation propagation in distributed systems.

Context cancellation allows aborting a chain of distributed requests to save resources if the client disconnects or times out.

When an HTTP server receives a request, it generates a Context. If that server makes a gRPC call to another service, it passes the Context. If the user closes their browser, the initial context cancels. The HTTP server aborts its work, and the gRPC client intercepts the cancellation and forwards a cancellation frame over HTTP/2, halting the downstream service.