nodesByIsolation

nodes ordered by how alone each one is: fewest neighbours within radiusPx first.

This is the order to rasterize chips in. A node the source draws on its own has, by definition, few neighbours, so the ones that need a chip most sort to the front — and the ones just past the cluster threshold, where unclusteredNodes is most likely to have guessed wrong, come next rather than last. That makes the image budget run out on nodes buried mid-cluster, which are never drawn anyway.