The key I'm using to track uniqueness isn't optimal because a single Caddy module may register multiple collectors. Extracting the unique identifiers using the Describe method is hard because theDesc type only has String method, and it's hard to extract both fqName and the const labels (unique combo) from the string. So I changed it to just swallow the duplicate registration error but bubble the rest. I doubt it's best-practice but cannot think of a better way.

That does sound like a tricky one. That's probably fine? We can see if it causes any issues but maybe it's not too likely, or is at least preventable.