Function tail 

pub async fn tail(
    url: &str,
    identity: &Identity,
    session: &str,
    channel: &str,
) -> Res<()>

Joins channel and streams its traffic to stdout until Ctrl-C — the minimal human “watch the agents talk” view (PRD-0011 T-004; the §19 aggregation log’s smallest sibling). App-level pings keep the session inside the server’s idle-reap window.

Errors

Returns an error if the connection, authentication, or join fails, or the link drops.