Function resolve_auto_with 

pub fn resolve_auto_with(
    is_macos: bool,
    wayland: bool,
    x11: bool,
    has: &dyn Fn(&str) -> bool,
) -> Backend

Pure core of resolve_auto (OS / display / tool-presence injected for testability): macOS -> osascript; Wayland -> wtype then ydotool; X11 -> xdotool; else the safe log backend.