I'm looking into lnprototest. It's a test suite that can be used to check whether an implementation is spec-compliant or the spec needs to be more precise.

But even if every implementation tested itself against it, and the spec would leave no room for interpretation, we still wouldn’t catch issues like this in advance, because, as you mentioned, probing isn’t part of the spec.

Hmm, tough spot to be in. Here's a hug emoji: 🫂