Function to_server_hex 

fn to_server_hex(value: &BoxedUint) -> String

Hex in the exact format 1Password’s server expects: lowercase, with all leading zero nibbles stripped. The output may be odd-length; that is intentional. Both userA (sent over the wire) and u (the SRP shared secret hashed into the session key) use this encoding, and changing it would break wire compatibility or session-key agreement with the server.

Mirrors the official 1Password JS client (webapi bundle): q = e => e.toString(16).replace(/^(0x)?0*/, "")