docs: @Override
      public <T> CompletionStage<T> buildCompletion(Graph graph) throws UnsupportedStageException {
  
          PrivilegedAction<CompletionStage<T>> action = new PrivilegedAction<CompletionStage<T>>() {
              @Override
              public CompletionStage<T> run() {
                  return WASReactiveStreamsEngineImpl.super.buildCompletion(graph);
              }
          };
  
          WSContextService contextService;
          if (contextServiceRef != null) {
              contextService = contextServiceRef.getService();
          } else {
              contextService = null;
          }
  
          StreamRunner<T> runner = new StreamRunner<>(getExecutor(), contextService, action);
  
          StreamTask<?> streamTask = runner.startStream();
  
          CompletableFuture<T> wrapper = (CompletableFuture<T>) streamTask.getWrapperCompletableFuture();
  
          return wrapper;
      }