code: public Spore<I,O> setForEach(Callback<O> cb) {
          if ( localCallback != null ) {
              throw new RuntimeException("forEachResult callback handler can only be set once.");
          }
          localCallback = cb;
          return this;
      }
docs: use local (sender side). Register and receive data streamed back from remote spore execution.
  
  @param cb