A more general solution to this is that Minecraft supports checking if you can put an item into a slot. I'm sure some mod somewhere will Mixin to this, so calling this for any time we put something into a slot seems like a good idea. This should also fix the Shulker issue while we're at it.

EDIT: I don't see many restrictions outside Shulker Boxes and the furnace fuel slot, so will just fix for Shulkers