Function apply_container_frame 

pub fn apply_container_frame(
    container_transform_and_bounds: TransformAndBounds<NodeLocal, Window>,
    container_frame: Option<ContainerFrame>,
) -> TransformAndBounds<NodeLocal, Window>

Apply a container-assigned child frame on top of the parent geometry.

This is the geometry seam where container-owned placement can cooperate with descendant-authored layout and future bottom-up measurement.