On the frontend, updates the route path to include the (base64-encoded)
url. Uses that and the load-single functionality to support loading
directly into a submission page, which fetches just the requested
submission.
Also ensures we don't open duplicate comment subscriptions.
Base64 encoding isn't actually @ta-safe, since it contains capitals and
=. +wood escapes all such characters explicitly. The result is more
readable and more hoon-native paths, but does mean clients will have to
re-implement +wood locally.
