The extensions are automatically called by the framework and there are only limited capabilities to communicate between the plugins. It is also important to understand that a save in a follow up action will cause a new save event and a subsequent call of all related pre conditions and follow up actions (process advisors and - participants).

The easiest way to pass information is to use additional save parameter - basically a string - during work item save. The parameter will be available to the subsequently called process advisors and - participants. This can be used for the abve purpose and to prevent recursive descent as well. See  https://rsjazz.wordpress.com/2016/10/24/using-the-work-item-server-api-to-create-work-items/

	Set additionalParams = new HashSet();
	additionalParams.add(ICreateTracedWorkItemsParticipant.CREATE_TRACED_WORKITEMS_PARTICIPANTS_ACTION_SAVENEW);

	fWorkItemServer.saveWorkItem3(newWorkItem, null, null, additionalParams);
	return newWorkItem;