Function start_hidden 

fn start_hidden(login_start: bool, tray_unavailable: bool) -> bool

Should this host hold its “main” window hidden (SPEC_START_WITH_OS_2026_09_25.md §3.3)? Only for a login start, only when the tray is up (no tray means a normal window, never an invisible process), and only for the first host: a host restarted after a crash must come back visible, since the user may already have been using it.