After a week of work, lots of head scratching, I've managed to draw all these different-looking menus, with a single #uxn file that is shared by these different projects.
The menu drawing code has no actual drawing code, but instead uses each app's own string drawing routines.
https://git.sr.ht/~rabbits/noodle/tree/main/item/src/manifest.tal
I may not be able to have two tabs open at once on this fucking computer, but I can have ad infinitum of uxn instances!