In C# I’m generally using Verify for these happyflow tests (...)

I don't think this is related to this topic. The problem domain cover the exact opposite of happy flow tests: it's about maximizing edge case coverage by minimizing the amount of tests required. This has nothing to do with what invariants you're tracking, but how many tests you are using to cover the paths you're covering and how to tell which tests you can dump while keeping the same coverage.