Function bitwarden_later 

pub(crate) fn bitwarden_later(
    qt: &CxxQtThread<Sioul>,
    work: impl FnOnce() -> String + Send + 'static,
) -> i32

Bitwarden’s calls that wait for its server (an unlock, a passkey, the e-mail’s code), made off the window’s thread so that it never freezes meanwhile: a ticket at once, then work’s answer with bitwarden_answered(ticket, answer) on the window’s thread. The dialog waits for its own ticket, saying so (VaultUnlock.qml).