What I could do is pick an instance at random and see if I can write that instance to app storage that persists on reinstall. That way, they don’t lose their account by not remembering what instance. That doesn’t solve the web.

The issue is password managers save username and password, but I need to save instance as a 3rd value. I wonder if I can prepend the instance to the front of their username in a way that the password manager picks it up, then slice it off later when they log in. But that’s kinda hacky.