@Observe the events raised during the processing of that annotations: org.jboss.seam.initProcess.<process-name>, org.jboss.seam.startTask.<task-name>, etc

Yes, there are.

Either let Seam to inject the TaskInstance (@In TaskInstance taskInstance) or use org.jboss.seam.bpm.TaskInstance.instance()) in order to get the org.jbpm.taskmgmt.exe.TaskInstance.

Then, of course, taskInstance.getId() will give you the taskInstanceId.

The same apply for BusinessProcess.

@In TaskInstance taskInstance;

@Observe("org.jboss.seam.startTask.mytask")
public void taskStarted()
{

   log.debug("The task mytask with id = {0} was started.", taskInstance.getId());

}