awaitRequestCancellable
suspend fun <T> CancellationSupport.awaitRequestCancellable(callId: RpcCallId, response: Deferred<T>): T
Await response and, if the awaiting coroutine is cancelled before completion, invoke CancellationSupport.sendCancel for callId before re-throwing.
This is the client-side half of the cancellation mechanism — transports that track pending calls should route their stub-side call(...) through this helper so that cancellation is forwarded to the remote end.