Function push_pin_rows 

fn push_pin_rows(shape: &ShapeRef<'_>, offset: Vec2, out: &mut Vec<Candidate>)

Each pin’s stub row: a horizontal guide at the stub’s y, shifted by offset. Only the row is offered — a pin sits at a fixed offset from the edge it attaches to, so its x is not a meaningful alignment feature (the edge is); its y lets pins on different blocks line up. Works for block pins and the port pin.