Function multi_source_dijkstra_nearest_source 

pub fn multi_source_dijkstra_nearest_source(
    graph: &Graph,
    sources: &[&str],
    weight_attr: &str,
) -> Vec<(String, String)>

br-r37-c1-2z0mw (cc): multi-source Dijkstra returning, for each reachable node, the SOURCE (center) on its shortest path — i.e. path[0] of multi_source_dijkstra — WITHOUT building any paths. voronoi_cells only needs this mapping; propagating the source label (source[v] = source[u] on each relaxation, exactly where the path kernel does path[v] = path[u] + [v]) and skipping the all-paths String construction is the fix. Emitted in finalize (distance, push-seq) order — identical to the path kernel’s key order — so {node: source} is byte-identical to {v: paths[v][0]}.