This is a clusterfuck.

Just use SimpleX. SimpleX can be integrated with nostr for some good UX without much effort:

- Users create a public SimpleX address, this contains an X25519 DH key.

- The DH key (just the DH key, no server information) gets published on the user's nostr profile, there will be a field for that. The profile is digitally signed by the user's nostr public key so no mistaken identities here.

- All nostr relays act as SimpleX servers.

- When sending a message to the user, the nostr client will probe all known relays to see whether there is a SimpleX queue that accepts the DH key (discovery process).

- nostr client hands DH key and server information to the SimpleX app.