code: @CommandArgument
    public void clean() {
      for (int i = 0; i < jobProgressStates.size();) {
        ProgressState state = jobProgressStates.get(i);
        if (state.isCancelled() || state.isComplete()) {
          jobProgressStates.remove(i);
        } else {
          i++;
        }
      }
    }
docs: Removes completed and cancelled jobs from the stat list.