As a supervisor I 'hold' the supervisee and accept the unknown and the unexpected. supervision should provide a release for the supervisee which in turn enables their clients.
In my supervision practice I am non-directive as directing a supervisee would be in contradiction with their ability to take autonomous decisions. It is the supervisee who brings 'the agenda'.
On the other hand it is important to, where appropriate, take authority in an accepting and respectful way because a balance between a facilitative and authoritative stance makes effective supervision.
Taking authority should not be confused with being authoritarian which has no place in supervision.