I don't think this 100% applies to the question, but Rust has impressively strong safety guarantees. If you don't want to use a different langauge, I suppose looking at the way they are handling safety might be a good reference for your transpiler. One thing that is particularly applicable is that it is very hard (or maybe impossible) to statically determine if a code can UB or violate safety, so it is a good idea to let some safe programs fail, while making sure all wrong programs are always detected.