"missing something in my case analysis. If a negative object intersects a positive object, that is ambiguous. You could resolve this by ignoring the negative object in this case. Yeah, that's an arbitrary choice, but any implementation of the idea would need to pick an unambiguous set of rules"
Absolutely, that is part of the larger set of conceptual issues with negative spaces.
As things are now, if you union two objects, you get get an object that has a "volumeicity" of 1. With a negative object you have a volumeicity of -1.
Then you have to decide what is the volumeicity of the union of two negative objects. Is it -1, -2, or 0, or even 1?
And then define what you expect the difference operation is supposed to do with a negative space.