how do nostr apps talk to it? is it always hosted on the same local port?
For now its always the same port. You can just use it like a relay ws://localhost:7777
any idea if mobile web browsers are allowed to talk to localhost?
Yes, just tested now using nostrudel posting a note worked
I think only tor browsers can
noob question, is this used for caching or does it replace the relays hosted on web?
Caching
would it make sense to use the same port as the nostr relay tray app? 4869
Sure i can change it