Function begin_on_server 

pub(crate) fn begin_on_server(
    login: &Login,
    place: &str,
    passphrase: &str,
    again: &str,
    signed_in: bool,
    may_start: bool,
) -> Result<Begun, String>

Sharing begun through place among login’s files, Sioul keeping the folder itself (remote::MIRROR): joined when another device shares through it already (its seal, the passphrase chosen there, typed once and checked against it), else, when may_start, made there and sealed (the passphrase typed twice); a join that finds no seal there, nothing made. signed_in: login is the server’s own sign-in’s (loginflow), the folder kept with it (remote::begin_signed_in). On the calling thread, never the window’s: which, or why not, in words.