Just an update: Psychic guards remain in effect.
I took my beach-landed Polymorpher Bruno and snuck him out of the fort, without being seen, then teleported him immediately back to the underground shrine and up and out. The guards aggroed on him for no reason.
Bruno woke up on the beach and entered the fort. No one ever made him register or put his name in a book. In fact, given the side ladder, I believe it's actually completely possible for no guards to EVER catch sight of Bruno. What do you want to bet that even then if Bruno has never been seen by a guard, they'll attack him on sight if he leaves the fort for three seconds and then comes back?
I don't know what "problem" Larian is trying to solve, but having the guards aggro on people who have left Fort Joy makes LESS sense than them NOT.
The guards do not care at all what happens to the prisoners. At all. Prisoners fight and kill each other all the time. Guards do nothing. Prisoners can come and go out the west gate so I'm not even sure what those guards are there for. Four guards guard the main gate. One guard with a dog patrols a small area of the camp. At least half the prisoners are out of sight of guards at all times. You can spend tons of time out of sight of guards.
And yet step outside the camp for a few seconds and somehow all guards know you escaped. It's not that the collars are tracking devices, because you can have free reign of the restricted areas in the fort and no one goes to stop you, and no one goes to track you down outside the fort either.
There is no sensible reason why leaving the fort unseen should trigger magic switches to make all guards attack you on sight. Guards have been shown to have no interest in keeping track of prisoners.
