Fort should more or less be treated the same way as a herald would be. If they are directly between you and a mage then they chose to be in a bad spot.
You have a right to defend yourself but you can't go out and hunt non mages/scions/nexuns/cabals village is formally at war with.
By and large that boils down to, let them strike first if you can afford it (some situations you really can't allow that, biggest one being if they can sleep you). In those situations you make it loud and clear. I am here, you come at me your going to get the axe, then you stand your ground and wait.
This is really no different than how a member of maran deals with aggresive neutral characters, except there is less of an expectation that you just stay out of the way since villagers have a more machismo culture.