Core-SG Graph

The support graph stores enough edge information to support later MST extraction for valid target k values. In the exact path, Core-SG builds a k-nearest-neighbor graph from the dense pairwise distance matrix and augments the metric edge set with reference MST edges from the k_max fit.

The graph is stored as arrays with edge endpoints and weights. metric_edges_ keeps original metric distances, while support_graph_ is reweighted later for a target k.

This separation lets Core-SG reuse the same structural support while changing the mutual-reachability weights for each extraction.