I have a procedural model that occupies 3-5 UDIM tiles and I want to use the new adjacency workflow with UDIMs, the old workflow to make UDIMs has an input for camera_ref on the rasterize geo node which is where the math UDIM node could be plugged in, how do I rasterize UDIMs with Adjacency?

Rastering UDIMs with adjacency won't help you much, as when you go to _use_ the adjacency maps you then need to jump between all possible UDIMs when you leave an island.

You need to make a utility-texture coordinate system for use with the adjacency maps. It often is useful to have a separate texture coordinate for adjacency as you can increase padding. Then the idea is to synthesize the adjacency aware operations through this utility map. Then each UDIM can read off the utility map to get its values.