[AnimalMuppet]

To expand on your first and last points:

Your researcher got a result. Great. What is their objective evidence that the result is real rather than an artifact of a bug in their code? If the code is garbage, you can't trust the result, no matter how much of a breakthrough the result would be if true.

That doesn't mean that the code needs to be production-ready. It does mean that the code needs to be clean enough to be trustworthy. (Tests can be included in this evaluation.)

If the code's going to be product-ized... maybe ask the researcher which parts of the code they think are the most troublesome. Start by re-writing those pieces, from scratch, with production levels of rigor. Then, as other parts prove troublesome, rewrite those too. Don't band-aid them, rewrite them. Keep the interfaces, unless the interface itself is part of the problem.