facett-core — the visual kernel. Render a node/edge Scene into egui.
Source-agnostic: build a Scene from anything (Arrow rows, a graph, a DAG),
hand it here, get pixels. The CPU painter is the reference; a wgpu fast
path (GPU viewport-cull + indirect draw, seeded from katana-osm's
osm-viewer) lands behind this same draw() call — consumers don't change.