code: @Override
      @CallerSideMethod public void subscribe(Subscriber subs) {
          // need callerside to transform to Callback
          Callback callback = (r, e) -> {
              if (Actors.isResult(e))
                  subs.getReceiver().receive((ChangeMessage) r);
          };
          _subscribe(subs.getFilter(), callback, subs.getId());
      }
docs: remote receiver then builds a unique id by concatening localid#connectionId