supports-thickness slider — relative shaft width for supports edges

A LINEAR 0–1 multiplier of Edge width (default 0.5, dead-center at step
0.1 — 11 stops like the ladder rows but ratio-valued), grayed out by the
supports-edges toggle (the Dilation dependency pattern). Renderer splits
supports shafts into their own Path2D and strokes a second pass at
edgeWidth × supportsWidth; arrowheads stay full-geometry in the one shared
path (owner pick: shaft only). A true 0-width stroke is undefined on
canvas — the 0 end floors to a 0.5px on-screen hairline; hiding remains
the toggle's job. Sanitizer: real numbers clamp to [0,1], everything else
resets to 0.5; clamps pinned in render-settings.test.

src/core/render-settings.ts

@@ -59,6 +59,14 @@ export interface GraphRenderSettings {
 	 *  them (settings never shift the graph: camera, one frame), and node
 	 *  detail cards still list them. */
 	showSupports: boolean;
+	/** Relative SHAFT thickness of supports edges (owner, 2026-09-29):
+	 *  a 0–1 multiplier of edgeWidth — default 0.5, the single-line
+	 *  relation reads as the lighter one. SHAFT ONLY: arrowheads keep
+	 *  full Arrowhead-size geometry (owner pick). Linear, not a ladder —
+	 *  it's a ratio; exactly 0 floors to a hairline in the renderer
+	 *  (canvas cannot stroke a true 0-width line; hiding is the toggle's
+	 *  job). */
+	supportsWidth: number;
 	/** Toggle for the cluster region labels (hulls always draw). */
 	clusterLabels: boolean;
 	/** Cluster label font size, px on screen (camera-compensated —
@@ -102,6 +110,12 @@ export function sanitizeRenderSettings(raw: unknown): GraphRenderSettings {
 		labelSize: legacySizes ? DEFAULT_RENDER_SETTINGS.labelSize : ladd(r.labelSize, LABEL_SIZE_LADDER, DEFAULT_RENDER_SETTINGS.labelSize),
 		showSupports:
 			typeof r.showSupports === "boolean" ? r.showSupports : DEFAULT_RENDER_SETTINGS.showSupports,
+		// Linear ratio, not a ladder: real numbers clamp to [0, 1]; anything
+		// else resets to the default.
+		supportsWidth:
+			typeof r.supportsWidth === "number" && Number.isFinite(r.supportsWidth)
+				? clamp(r.supportsWidth, 0, 1)
+				: DEFAULT_RENDER_SETTINGS.supportsWidth,
 		clusterLabels:
 			typeof r.clusterLabels === "boolean" ? r.clusterLabels : DEFAULT_RENDER_SETTINGS.clusterLabels,
 		clusterLabelSize: ladd(
@@ -270,6 +284,7 @@ export const DEFAULT_RENDER_SETTINGS: GraphRenderSettings = {
 	labelZoom: 4,
 	labelSize: 3,
 	showSupports: true,
+	supportsWidth: 0.5,
 	clusterLabels: true,
 	clusterLabelSize: 14,
 	regions: DEFAULT_REGION_TUNING,