Ok I have basic NIP-89 support in gossip, coming soon to master branch.

* Subscribes to handler recommendations (31989) from all the people you follow
* Pulls handlers (31990) for all recommendations and saves locally
* Registers handlers against event kinds if they provide a "web" "nevent" url (for normal kinds) or a "web" "naddr" url (for addressable kinds)
* Event menu lets you "Open With" any of these handlers
* You get a page where you can disable any of these that you don't want on a per-kind basis so they don't clutter your menu.

You cannot manually add or edit handlers, and I don't plan to do that (apps developers should be doing that for their apps)
You cannot recommend handlers to your friends yet, but I will add that.