It's an interesting idea - sadly the problem with it is that there's no way to add these tags to other kinds of files that don't have frontmatter. Not sure how to best to deal with it. Right now I'm leaning towards having some vault-specific storage for it.

Ah yep, I hadn't considered these codes appear for all files, not just frontmatter-friendly formats, which my vaults mostly are… Watermarks for media files? EXIF? — I joke.

It's an interesting problem to think on and also reminds me of resource fork advantages. My two cents is it's worth having a setting for "more permanent" codes at whatever compromise it forces. The idea of very short note codes is really nice, especially if it's "that's the code, it won't change" (I constantly rename and move notes to improve organisation and I expect others do) — I'll be trying out your plugin soon!

The Git idea was to track the original commit of note, assuming the vault is in a repo, and use that original path + git hash as the thing that doesn't change. Log tracking is imperfect, but I'd expect it to work in a vast majority of cases in Obsidian context.