I am creating a 2.5D game where the player can create stairs that then become an offmesh link between the floor and a second platform that the stairs connect to. prior to implementing navigation I had code in place where the AI characters would pass through the stairs if approaching from the backside but now with the navigation in place im not sure how to have this same functionality. The stairs and offmesh link must stay active since other AI characters may be using them, only the characters approaching from behind the stairs should pass through. I also need help on how to have the pathfinding understand that they can pass through the stairs and not see it as an obstacle. Thanks in advance for any help!
Disabling BiDirectional checkbox on Offmeshlink, should do what you want.
https://docs.unity3d.com/Manual/class-OffMeshLink.html
Bi-Directional - If enabled, the link can be traversed in either direction. Otherwise, it can only be traversed from Start to End.