pub fn utility_interface(
declared: &[String],
exists: impl Fn(&str) -> bool,
) -> Result<String, String>Expand description
Pure: the box’s utility NIC: the last interface the net spec declared that this box
has (exists). A box laid behind its front (the lean estate) has its utility NIC alone, and
it boots the same two-NIC spec, so its one NIC is the utility one. No NIC is a named refusal,
never a wildcard.