fn for_its_address(cert: Cert, address: &str) -> Option<Cert>Expand description
cert with only its user IDs for address, when one of them is bound
to it (names); none otherwise. What a certificate brings from
elsewhere (an Autocrypt header, a lookup) is kept for the address it
came for alone: its other user IDs, bound or not, never make it
another address’s key (review of 19 October 2026, F2).