Function resolve_envelope_keys 

pub fn resolve_envelope_keys(
    peers: &[SocialPeer],
    dids: &[String],
) -> Vec<(String, String)>

Resolve dids to (did, envelope_pubkey_hex) pairs from peers — the parties whose envelope key is known. Parties without a published key (or not peered) are simply omitted (the caller learns which keys are still missing by comparing lengths). Pure; unit-tested.