Enum Invite 

pub(crate) enum Invite<'a> {
    File(&'a str),
    Pair(String, String),
}

Where the credential that redeems an invite came from.

Two shapes because there are two readers. An agent is handed a file by whatever provisioned it; a person is handed a link in a chat window, and the link is the credential — writing it to a file first so this could read it back would be asking them to do by hand the one step this command exists to remove.

Variants

File(&'a str)

A file holding one <id>:<secret> line.

Pair(String, String)

The two halves, lifted straight out of a join link.