Allow admins to select a system role and view all users currently assigned to it — consistent with how custom roles already work.
Current behavior:
For custom roles, admins can select a specific role and see the list of users who have it enabled (forward + reverse lookup both work - see image #2 “stack manage”).
For system roles, only the forward lookup is possible (user → role). There's no way to select a system role and see which users have it assigned as “
System roles cannot be managed”.
