I’ve done some integer/“lining up” work as you mention with core.logic: https://www.lvh.io/posts/solving-regex-crosswords/ — but I don’t think that’s what I’m looking for here; I’m expecting, largely, everything to be ground and monotonically solvable.

The underlying use case here FWIW is for some mortgage math. The problem with a spreadsheet is that you have to decide in advance which values depend on which; I’d like to make slightly more complex changes involving a solver, e.g. what happens if you change this variable vs this variable; but it’s still all monotonically solvable and doesn’t require anything fancy a la polynomial solvers or Gaussian elimination or anything like that.