message: ADRecordingSession: box up computations using scopes
diff: @@ -121,9 +121,11 @@ struct DiffVCall : CustomOp<Type, Result, ConstStr, Self, Func, Args...> {
  ADRecordingSession() : m_status(ad_flag(ADFlag::Recording)) {
  ad_clear_dependencies();
  ad_set_flag(ADFlag::Recording, 1);
  + ad_prefix_push("Recorded VCall");
  }
  ~ADRecordingSession() {
  ad_set_flag(ADFlag::Recording, m_status);
  + ad_prefix_pop();
  }
  int m_status;
  };
  