The proxy emits 5XX errors in a number of cases (such as when a request's dispatch timeout is exhausted). However, this is very confusing for grpc clients, who receive errors such as:

rpc error: code = Unavailable desc = Service Unavailable: HTTP status code 503; transport: missing content-type field

It seems like it should be possible for us to set an appropriate grpc-status/message on responses when failing requests that include the appropriate content-type? This should make it much easier to debug these errors.