Users need to know when an action card or subaction has been assigned to them. On mac, there should be an icon bounce when new action cards have been assigned to the specific user while the application has been minimized/closed/inactive. In addition to this, there would be a sound notification that would go off signifying an action card has been assigned to the user. The sound should be unique to the Hive application as to not mix up with other system notification sounds/pings. This is a common UX that many messenger services also have (ie. Slack, Outlook, etc.), if reference is required.