Is the idea that "accidental casework" should be moved up, whereas the "reusable bulk ontology" should be moved down?

There's very high-leverage abstractions that completely constrain a space. An example is a good definition - you can't think of something outside to compare it to, it just is. These things survive for a long time since they define it.

But if you're trying to do that philosophy super deep into a program, you're probably violating a bunch of invariants subtly.

Of course, there is no good separation at the end of the day as we all know from spaghetti codebases :)