Function route_to_head 

pub fn route_to_head(
    router: &mut ClosedRouter,
    fixed: &FixedLegs,
    head: Point,
) -> Vec<TaggedPoint>

Append the trailing head leg (fixed.tail → head) to the fixed legs — the only part that changes as the cursor moves. head is typically not a graph node, so this leg is the L-path fallback. Together with route_fixed_legs this equals RouteRequest::route with SelfCost::Skip.