Function render_shift 

pub fn render_shift<'a>(
    attachments: &'a Attachments,
    id: &'a str,
    graph: &PoseGraph,
) -> Result<(f64, f64), PoseGraphError>

The render-time shift from id through its chain: each link’s measured offset plus how far its anchor node has since moved under graph relaxation (as of the attach frame), so an attached fragment follows a target that a later loop closure moved. Summed link by link as shift += dx + correction.