Function widget 

pub(crate) fn widget<C: Canvas>(
    data: &Drawing<'_>,
    interaction: &Interaction,
    painter: &mut Style<'_, C>,
) -> ControlFlow<Option<Transition>>

Select-tool entry. Renders the route-start target on the nearest anchor and, on a click or drag of it, hands off to the route tool. Break means the pass owns this frame’s interaction (carrying the tool switch, if the gesture produced one); Continue falls through to the caller’s own handling.