Is there a way to send variables from a called process that triggers a bpmn error event back to the calling process? In particular, has any of the proposed syntax discussed at https://community.alfresco.com/thread/219599-output-variables-from-callactivity-on-boundaryevent-trigger been implemented?
Not from an error event, afaik. However a call activity has in/out parameters that can be used to transfer variables in/out.