OMG it all works. The annoying (literal) edge cases - I had a solution for them in mind, but I was worried it would need some fiddling. It did not - they Just Bloody Work. Better than expected in fact. Super excited, because this thing is actually practical!
I'm going to add a few more test models, and polish off some edges. But it's time to start writing some actual docs & some sort of "paper". Awesome!