Constant PEER_DENY_PREFIX 

pub const PEER_DENY_PREFIX: char = '!';

Marks a resolved peer entry as a deny rule rather than a grant.

Defined here because channel_external_peers writes the marker; the channel allowlist re-exports this constant rather than spelling the character again, so producer and consumer cannot drift. No chat platform admits a username beginning with !, and an entry that did would be denied rather than granted, so the reservation fails closed.