Function act_on_server 

fn act_on_server(
    qt: &CxxQtThread<Sioul>,
    shared: &Arc<Shared>,
    place: ServerRef,
    action: &str,
    target: &str,
)

An act on a message seen on its server only (a search’s): reading and flags at once, moves, archiving and the trash with “Undo”; what teaches the spam filter needs the message here first.