Hi there!
I forgot to update this thread, but after discussing this with some attendees in the Solid Symposium, we came up with a better solution (for now).
TLDR, the urls would be like this: https://my-app.com/recipes/pizza?id=https://my-pod.com/cookbook/pizza#it.
Basically, the full id would always appear in the url as a query parameter; and the short name of the recipe would only be used as a fallback. An additional benefit of this approach is that I could remove the viewer url altogether; and sharing recipes would be as easy as copy & pasting the url from the browser (provided it has the proper permissions, etc.).
I still haven’t implemented this approach in my apps, but it’s very likely that I do it next time I work on this.