Function default_binding_for 

pub fn default_binding_for(button: ButtonId) -> Binding

The canonical default Binding for a fresh button in the merged model.

ButtonId::GestureButton defaults to Binding::Gesture populated from default_gesture_binding — preserving the existing per-direction swipe behavior — so the GUI mode toggle and the runtime agree it starts in gesture mode. Every other button defaults to Binding::Single of its default_binding.

This is the seed when a button is first promoted to a gesture binding (see Config::set_gesture_direction), so a freshly-customized gesture button always carries a full default direction map — including a GestureDirection::Click — rather than a sparse map whose click would project to a no-op Action::None.