Usually the merge commit is what has the link to the PR/MR. So it's the best way to actually find it.

> Ultimately, these software development artifacts aren't relevant to the production state of the software you're deploying. It feels muddled to put an incomplete version of it into your tree when the better source of truth lives outside.

You could make the same claim about the entire history. Git is a development tool, production just needs a working cut of the source.