Function fold_member_geometry 

pub fn fold_member_geometry(
    hash: &mut u64,
    root_translation: Vec2,
    transform: &UiGlobalTransform,
    computed: &ComputedNode,
)

Fold one member’s root-relative geometry into a layer’s content hash: translation relative to the layer root (so moving the whole layer cancels exactly and never re-captures), the affine’s linear part (member scale / rotation), and the laid-out size. Quantized (1/64 px positions, 1/1024 matrix entries) so float ulp noise — (a+d)-(b+d) isn’t bit-exact — can’t flap the hash. Visit order is encoded implicitly by the fold sequence, so reorders change the hash too.