There's so much going on here it's hard to see what's doing what. Can you please add a few notes in the PR description explaining what all this PR is doing?

I don't think this PR is worth peer reviewing, it's not in a good state and it's not complete. It's not meant to be merged, it's kind of just a dumping ground for code I used to do investigation

Is there anything in this PR that's useful for understanding and/or evaluating the high level approach you're recommending in the issue? Currently the issue is more of an info dump than a "this is the recommended approach" so it's a bit hard to follow from that angle.

Closing this for now - we may end up copying some bits from this when we implement this validation in #329 but it likely won't use this exact PR.