Live physics drag + splat cluster regions

The renderer grows a live d3 sim (createGraphSimulation, shared with
the server settle): pointerdown on a node pins fx/fy and pointer capture
(preventDefault kills the compat mousedown, so d3-zoom never pans); the
first CLICK_SLOP-exceeding move reheats to alphaTarget 0.3; release
un-pins and the sim anneals (release-and-relax) — alpha < 0.005 settles
it, a 250ms debounced onCommit PUTs the rest state. Verified live: 123fps
during a 320ms drag (regions rebuilding every 3rd frame), 85-tick settle,
then zero idle frames. A slop-free press stays a click (select, no reheat,
no commit). PUT /api/graph/positions sanitizes (finite coords, known ids)
and if the graph grew mid-drag runs ONE incremental settle with the
client's arrangement as anchors (50-id PUT test: anchored drift 0.15).

Cluster regions swap convex hulls for a low-res world-space SPLAT bitmap:
per-member radial-gradient discs (alpha 0.2) + intra-cluster edges as
round-cap strokes (Minkowski dilation — concave shapes finally render),
upscaled with bilinear smoothing (the upscale IS the blur, no ctx.filter:
Safari). One tiny blit per frame replaces 32 clusters x 4 offset
Path2D polygons re-rasterized at DPR 2 (the old GPU coil-whine path);
during the live sim the bitmap rebuilds every 3rd frame. cluster-geometry.ts
retires convexHull/offsetPolygon/traceRoundedPath (tests follow; clusterHue
stays). Region labels stay (centroid + clusterHue, inverse-gated on zoom).

components/graph-view.tsx

@@ -408,6 +408,15 @@ export function GraphView() {
 			onStageClick: () => setSelected(null),
 			// Any camera move detaches the card from its node — close it.
 			onCameraMove: () => setSelected(null),
+			// Live physics settled: persist the new rest state. Fire-and-
+			// forget — the next snapshot fetch carries the ledger anyway.
+			onCommit: (positions) => {
+				void fetch("/api/graph/positions", {
+					method: "PUT",
+					headers: { "Content-Type": "application/json" },
+					body: JSON.stringify(positions),
+				}).catch((err) => console.error("[graph] positions commit failed", err));
+			},
 		});
 		rendererRef.current = renderer;
 		return () => {