Function inbox_room_id 

pub fn inbox_room_id(fingerprint: &str) -> String

huddle 1.0: a stable, per-identity “inbox” room id for relay-routed contact requests — inbox:<hex(sha256("huddle-inbox-v1" || fingerprint))>. Lets “add by HD-ID” work over the internet (not just the LAN mesh): the requester publishes a signed ContactRequest here and the owner, who auto-subscribes to their own inbox, picks it up (live or from the relay mailbox). The relay only ever sees this hash, never the raw fingerprint (preimage resistance), so it can’t reconstruct a contact graph; the inbox: prefix + distinct salt keep it from colliding with DM / group room ids. Both sides derive the same id from the target fingerprint.