Function resize_pin_shift 

pub fn resize_pin_shift(
    offsets: impl Iterator<Item = u32>,
    new_height: f32,
) -> u32

How many slots every pin shifts up when a block holding pins at offsets is resized to new_height px, so the lowest pin keeps its bottom clearance instead of blocking the resize. Bounded by the top margin (the smallest pin offset) so the highest pin never rises above slot 0. Zero when the pins already fit — i.e. only a height that would push the lowest pin out shifts them.