follows renders as the double-shaft glyph (⟹), supports stays single

Per docs/vision-edge-glyph.md: a `follows` edge (the derivation backbone)
draws two parallel shaft tails offset along the edge normal by a fixed
SCREEN-space gap (FOLLOWS_GAP_RATIO x edgeWidth — constant on screen at
every zoom, like the stroke width), converging on the shared single
arrowhead; `supports` keeps the plain single line (dashed was rejected
earlier — not revisited).

- CanvasEdge carries the edge type; graph-view passes it from the snapshot.
- followsEdgeGeometry (pure, tested): offset tails + convergence at the
  head base — a strictly-parallel pair would poke out beside the head
  whenever the screen-fixed gap exceeds the head's world-scaled base
  half-width. The offset tails sit farther from the source center than
  the axis start, so the source disc never clips them.
- Edge paths leave buildGeometry: their gap is anchored to the CURRENT
  camera scale, so buildEdgePaths(k) rebuilds on geoVersion changes and
  camera-scale drift (> EDGE_PATHS_ZOOM_EPSILON) — 0.08ms per rebuild at
  211 edges; pans and settle frames reuse the cached paths.
- Legend entry bottom-right: ⟹ follows · → supports.

Live-verified: isolated follows edge (search "likelihood") shows two 1px
shafts with a ~3px centerline gap converging into one 8px-base shared
head; gap measured constant on screen at 0.2x, 1x, and 5x fit zoom while
heads/nodes scale. Gates: tsc, 435/435 tests, lint, build.

components/graph-canvas.ts

@@ -64,6 +64,7 @@ import {
 	sanitizeRegionTuning,
 	type PhysicsTuning,
 	type RegionTuning,
+	type EdgeType,
 	INCREMENTAL_GRAVITY,
 	LINK_DISTANCE,
 	type DepthAnchorMode,
@@ -88,6 +89,10 @@ export interface CanvasNode {
 export interface CanvasEdge {
 	from: string;
 	to: string;
+	/** Relation type: `follows` renders the double-shaft glyph (⟹),
+	 *  `supports` the plain single line (DECIDED 2026-09-14,
+	 *  docs/vision-edge-glyph.md). */
+	type: EdgeType;
 }
 
 /** One cluster region: member node ids + the LLM-coined label (or null). */
@@ -166,6 +171,16 @@ const COMMIT_DEBOUNCE_MS = 250; // settle → ledger PUT delay (new drags cancel
 const REGION_EVERY = 3; // live-sim frames: rebuild every Nth, blit the rest
 const REGION_LABEL_SIZE = 14;
 
+/** Follows glyph: screen-space distance between the two shaft CENTERLINES,
+ *  in units of the edge stroke width (constant on screen — so the gap is
+ *  too, at every zoom; DECIDED 2026-09-14, docs/vision-edge-glyph.md).
+ *  3× a 1px stroke = 3px centers, 2px of clear space between the shafts. */
+const FOLLOWS_GAP_RATIO = 3;
+/** Rebuild the (zoom-anchored) edge paths when the camera scale drifts
+ *  more than this far from the scale they were built for — a handful of
+ *  cheap rebuilds per zoom gesture, zero per pan/settle frame. */
+const EDGE_PATHS_ZOOM_EPSILON = 0.02;
+
 
 /** One horizontal+vertical box-blur round over PREMULTIPLIED RGBA
  *  (Float32, stride 4, length w*h*4). Premultiplying first is what keeps
@@ -307,6 +322,46 @@ export function arrowGeometry(
 	};
 }
 
+/** The double-shaft glyph for a `follows` edge (⟹ — DECIDED
+ *  2026-09-14, docs/vision-edge-glyph.md): two shafts offset along the
+ *  edge normal by `gap` (a FIXED screen-space distance, world-converted
+ *  by the caller), converging on the shared single arrowhead — both
+ *  shafts meet at the head's base point. `supports` needs no helper
+ *  (the plain single shaft IS arrowGeometry). Pure: DOM-free, tested. */
+export function followsEdgeGeometry(
+	a: Pt,
+	b: Pt,
+	fromRadius: number,
+	toRadius: number,
+	headLength: number,
+	gap: number,
+): { shaftAFrom: Pt; shaftBFrom: Pt; shaftTo: Pt; tip: Pt; left: Pt; right: Pt } | null {
+	const g = arrowGeometry(a, b, fromRadius, toRadius, headLength);
+	if (!g) return null; // degenerate (coincident) — skip
+	const dx = b.x - a.x;
+	const dy = b.y - a.y;
+	const len = Math.hypot(dx, dy);
+	const nx = -dy / len;
+	const ny = dx / len;
+	const half = gap / 2;
+	return {
+		// Parallel tails at the source, ± half-gap along the normal. The
+		// offset starts sit FARTHER from the source center than the axis
+		// start (√(r²+half²) > r) — never clipped by the source disc.
+		shaftAFrom: { x: g.shaftFrom.x + nx * half, y: g.shaftFrom.y + ny * half },
+		shaftBFrom: { x: g.shaftFrom.x - nx * half, y: g.shaftFrom.y - ny * half },
+		// Convergence: both shafts end at the head's base point — the
+		// merge lands exactly where the shared arrowhead begins, clean at
+		// every zoom (a strictly-parallel pair would poke out beside the
+		// head whenever the screen-fixed gap exceeds the head's base
+		// half-width — the head scales with the graph, the gap doesn't).
+		shaftTo: g.shaftTo,
+		tip: g.tip,
+		left: g.left,
+		right: g.right,
+	};
+}
+
 /** Nearest node within maxDist of a screen point (linear scan — µs at
  *  our scale; a spatial grid only earns its keep past ~10k nodes). */
 export function pickNearest<T extends { id: string; x: number; y: number }>(
@@ -370,6 +425,7 @@ interface WorldSizes {
 	glowOuter: number; // hover halo outer radius, world units
 	labelSize: number; // node label font, world units
 	labelGap: number; // node edge → first label line, world units
+	arrowLen: number; // arrowhead length, world units (shared by both glyphs)
 }
 
 /** The pre-wrapped node name, centered below the node in WORLD units —
@@ -466,6 +522,10 @@ export class GraphCanvasRenderer {
 	// changes (geoVersion). Camera moves just re-rasterize the same paths.
 	private geoVersion = 0; // bump = geometry inputs changed
 	private builtVersion = -1; // version the cache was built at
+	/** Edge paths: built for this geoVersion AND this camera scale (the
+	 *  follows gap is screen-anchored). -1/0 force the first build. */
+	private edgeBuiltVersion = -1;
+	private edgeBuiltK = 0;
 	private nodesPath: Path2D | null = null;
 	private shaftsPath: Path2D = new Path2D();
 	private headsPath: Path2D = new Path2D();
@@ -482,7 +542,7 @@ export class GraphCanvasRenderer {
 	private frameCount = 0; // draw counter for the live-sim splat throttle
 	private labelLines = new Map<string, string[]>();
 	private worldLabelFont = "";
-	private world: WorldSizes = { nodeR: 0, glowOuter: 0, labelSize: 0, labelGap: 0 };
+	private world: WorldSizes = { nodeR: 0, glowOuter: 0, labelSize: 0, labelGap: 0, arrowLen: 0 };
 
 	constructor(canvas: HTMLCanvasElement, callbacks: RendererCallbacks) {
 		this.canvas = canvas;
@@ -938,14 +998,14 @@ export class GraphCanvasRenderer {
 		// Screen px at fit zoom → world units.
 		const s = 1 / this.kFit;
 		const nodeR = settings.nodeSize * s;
+		this.worldLabelFont = `${LABEL_WEIGHT} ${settings.labelSize * s}px ${data.fontFamily}`;
 		this.world = {
 			nodeR,
 			glowOuter: nodeR * GLOW_SCALE,
 			labelSize: settings.labelSize * s,
 			labelGap: LABEL_GAP * s,
+			arrowLen: settings.arrowLength * s,
 		};
-		this.worldLabelFont = `${LABEL_WEIGHT} ${settings.labelSize * s}px ${data.fontFamily}`;
-		const arrowLen = settings.arrowLength * s;
 		const visible = this.visible;
 		const isVisible = (id: string) => !visible || visible.has(id);
 
@@ -958,25 +1018,10 @@ export class GraphCanvasRenderer {
 		}
 		this.nodesPath = nodesPath;
 
-		// Edge shafts + arrowheads: tip lands on the target disc edge.
-		const shafts = new Path2D();
-		const heads = new Path2D();
-		for (const e of data.edges) {
-			if (!isVisible(e.from) || !isVisible(e.to)) continue;
-			const a = this.nodeById.get(e.from);
-			const b = this.nodeById.get(e.to);
-			if (!a || !b) continue;
-			const g = arrowGeometry(a, b, nodeR, nodeR, arrowLen);
-			if (!g) continue;
-			shafts.moveTo(g.shaftFrom.x, g.shaftFrom.y);
-			shafts.lineTo(g.shaftTo.x, g.shaftTo.y);
-			heads.moveTo(g.tip.x, g.tip.y);
-			heads.lineTo(g.left.x, g.left.y);
-			heads.lineTo(g.right.x, g.right.y);
-			heads.closePath();
-		}
-		this.shaftsPath = shafts;
-		this.headsPath = heads;
+		// Edge shafts + heads are NOT built here: the follows glyph's gap
+		// is anchored to the CURRENT camera scale (constant on screen), so
+		// buildEdgePaths(k) runs from draw() on its own schedule — geometry
+		// changes AND camera-scale drift (EDGE_PATHS_ZOOM_EPSILON).
 
 		// Cluster regions are NOT built here: they rasterize into their own
 		// low-res bitmap (see buildRegions), on their own rebuild schedule
@@ -996,6 +1041,60 @@ export class GraphCanvasRenderer {
 		ctx.font = prevFont;
 	}
 
+	/** Edge shafts + arrowheads (the relation glyphs). Own build schedule,
+	 *  separate from buildGeometry: the follows glyph's shaft gap is a
+	 *  FIXED screen-space distance (FOLLOWS_GAP_RATIO × stroke width —
+	 *  constant on screen at every zoom, docs/vision-edge-glyph.md), so
+	 *  in world units it scales with 1/k and must be rebuilt as the camera
+	 *  zoom drifts (EDGE_PATHS_ZOOM_EPSILON gates that — pans and settle
+	 *  frames reuse the paths). Cheap either way: ~hundreds of edges ×
+	 *  trivial trig, no rasterization. */
+	private buildEdgePaths(k: number): void {
+		const data = this.data;
+		const settings = this.settings;
+		if (!data || !settings) return;
+		const visible = this.visible;
+		const isVisible = (id: string) => !visible || visible.has(id);
+		const { nodeR, arrowLen } = this.world;
+		// The follows gap in WORLD units: constant on screen (· k stays
+		// FOLLOWS_GAP_RATIO × edgeWidth px at any zoom). Supports ignores it.
+		const gapW = (FOLLOWS_GAP_RATIO * settings.edgeWidth) / k;
+		const shafts = new Path2D();
+		const heads = new Path2D();
+		for (const e of data.edges) {
+			if (!isVisible(e.from) || !isVisible(e.to)) continue;
+			const a = this.nodeById.get(e.from);
+			const b = this.nodeById.get(e.to);
+			if (!a || !b) continue;
+			if (e.type === "follows") {
+				// ⟹: two parallel tails, one shared head.
+				const g = followsEdgeGeometry(a, b, nodeR, nodeR, arrowLen, gapW);
+				if (!g) continue;
+				shafts.moveTo(g.shaftAFrom.x, g.shaftAFrom.y);
+				shafts.lineTo(g.shaftTo.x, g.shaftTo.y);
+				shafts.moveTo(g.shaftBFrom.x, g.shaftBFrom.y);
+				shafts.lineTo(g.shaftTo.x, g.shaftTo.y);
+				heads.moveTo(g.tip.x, g.tip.y);
+				heads.lineTo(g.left.x, g.left.y);
+				heads.lineTo(g.right.x, g.right.y);
+				heads.closePath();
+			} else {
+				// supports: the plain single shaft (the majority relation
+				// stays light — dashed was rejected 2026-09-14).
+				const g = arrowGeometry(a, b, nodeR, nodeR, arrowLen);
+				if (!g) continue;
+				shafts.moveTo(g.shaftFrom.x, g.shaftFrom.y);
+				shafts.lineTo(g.shaftTo.x, g.shaftTo.y);
+				heads.moveTo(g.tip.x, g.tip.y);
+				heads.lineTo(g.left.x, g.left.y);
+				heads.lineTo(g.right.x, g.right.y);
+				heads.closePath();
+			}
+		}
+		this.shaftsPath = shafts;
+		this.headsPath = heads;
+	}
+
 	/** (Re)create the live sim from data.nodes at their current
 	 *  positions + the current physics tuning. Called by setData and
 	 *  setPhysicsTuning. */
@@ -1280,6 +1379,17 @@ export class GraphCanvasRenderer {
 		if (!this.nodesPath) return;
 
 		const { x: tx, y: ty, k } = this.transform;
+		// Edge paths: rebuild on geometry changes OR camera-scale drift
+		// (the follows glyph's gap is constant on screen, so its world size
+		// tracks 1/k). Pans and settle frames reuse the cached paths.
+		if (
+			this.edgeBuiltVersion !== this.geoVersion ||
+			Math.abs(k - this.edgeBuiltK) > this.edgeBuiltK * EDGE_PATHS_ZOOM_EPSILON
+		) {
+			this.buildEdgePaths(k);
+			this.edgeBuiltVersion = this.geoVersion;
+			this.edgeBuiltK = k;
+		}
 		// THE camera: one transform, then everything is world coordinates.
 		ctx.setTransform(dpr * k, 0, 0, dpr * k, dpr * tx, dpr * ty);
 

components/graph-view.tsx

@@ -753,7 +753,7 @@ export function GraphView() {
 				y: positions.get(n.id)?.y ?? 0,
 				label: n.name,
 			})),
-			edges: snapshot.edges.map((e) => ({ from: e.from, to: e.to })),
+			edges: snapshot.edges.map((e) => ({ from: e.from, to: e.to, type: e.type })),
 			clusters: snapshot.clusters.map((c) => ({ id: c.id, label: c.label, members: c.members })),
 			colors: {
 				node: tokenHex(NODE_COLOR_TOKEN),
@@ -896,6 +896,19 @@ export function GraphView() {
 				</div>
 			)}
 
+			{/* Edge glyph legend (bottom-right; the pipeline status pills own
+			    the bottom-left). ⟹ follows (the derivation backbone) · →
+			    supports — DECIDED 2026-09-14, docs/vision-edge-glyph.md. */}
+			{!isEmpty && (
+				<div className="pointer-events-none absolute bottom-3 right-3 z-10 flex items-center gap-2 rounded-full border bg-card/85 px-3 py-1.5 text-xs text-muted-foreground shadow-lg backdrop-blur">
+				<span className="font-medium text-foreground">⟹</span>
+				<span>follows</span>
+				<span className="text-muted-foreground/60">·</span>
+				<span className="font-medium text-foreground">→</span>
+				<span>supports</span>
+			</div>
+			)}
+
 			{/* Background pipeline status: what is currently running. */}
 			{pipelineRuns.length > 0 && (
 				<div className="absolute bottom-3 left-3 z-10 flex flex-col gap-1.5">

tests/graph-canvas.test.ts

@@ -13,6 +13,7 @@ import assert from "node:assert/strict";
 import { describe, it as test } from "node:test";
 import {
 	arrowGeometry,
+	followsEdgeGeometry,
 	boxBlurRound,
 	fitTransform,
 	labelAlpha,
@@ -113,6 +114,57 @@ describe("arrowGeometry", () => {
 	});
 });
 
+describe("followsEdgeGeometry (the ⟹ double-shaft glyph)", () => {
+	test("tails offset ±half-gap along the edge normal, converging on the shared head base", () => {
+		// Horizontal edge a→b: normal is (0, 1) — offsets are vertical.
+		const g = followsEdgeGeometry({ x: 0, y: 0 }, { x: 100, y: 0 }, 6, 6, 5, 4)!;
+		assert.ok(g);
+		assert.ok(Math.abs(g.shaftAFrom.x - 6) < 1e-9 && Math.abs(g.shaftAFrom.y - 2) < 1e-9);
+		assert.ok(Math.abs(g.shaftBFrom.x - 6) < 1e-9 && Math.abs(g.shaftBFrom.y + 2) < 1e-9);
+		// Both shafts converge on the SAME point: the head's base.
+		assert.deepEqual(g.shaftTo, { x: 89, y: 0 });
+	});
+
+	test("the offset tails sit farther from the source center than the axis start (never clipped by the disc)", () => {
+		const a = { x: 0, y: 0 };
+		const g = followsEdgeGeometry(a, { x: 100, y: 0 }, 6, 6, 5, 4)!;
+		for (const tail of [g.shaftAFrom, g.shaftBFrom]) {
+			assert.ok(Math.hypot(tail.x - a.x, tail.y - a.y) >= 6 - 1e-9);
+		}
+	});
+
+	test("shared head geometry matches the plain arrow (tip/base corners)", () => {
+		const a = { x: 0, y: 0 };
+		const b = { x: 100, y: 0 };
+		const plain = arrowGeometry(a, b, 6, 6, 5)!;
+		const g = followsEdgeGeometry(a, b, 6, 6, 5, 4)!;
+		assert.deepEqual(g.tip, plain.tip);
+		assert.deepEqual(g.left, plain.left);
+		assert.deepEqual(g.right, plain.right);
+	});
+
+	test("works at arbitrary angles (diagonal normal normalized)", () => {
+		// dir (0.6, 0.8) → normal (-0.8, 0.6); half-gap 1.5.
+		const g = followsEdgeGeometry({ x: 0, y: 0 }, { x: 60, y: 80 }, 10, 10, 8, 3)!;
+		assert.ok(g);
+		const ax = 0.6 * 10; // axis start
+		const ay = 0.8 * 10;
+		assert.ok(Math.abs(g.shaftAFrom.x - (ax - 0.8 * 1.5)) < 1e-9);
+		assert.ok(Math.abs(g.shaftAFrom.y - (ay + 0.6 * 1.5)) < 1e-9);
+		assert.ok(Math.abs(g.shaftBFrom.x - (ax + 0.8 * 1.5)) < 1e-9);
+		assert.ok(Math.abs(g.shaftBFrom.y - (ay - 0.6 * 1.5)) < 1e-9);
+	});
+
+	test("null for coincident endpoints (same guard as the plain arrow)", () => {
+		assert.equal(followsEdgeGeometry({ x: 5, y: 5 }, { x: 5, y: 5 }, 6, 6, 5, 4), null);
+	});
+
+	test("zero gap degenerates to the plain single shaft", () => {
+		const g = followsEdgeGeometry({ x: 0, y: 0 }, { x: 100, y: 0 }, 6, 6, 5, 0)!;
+		assert.deepEqual(g.shaftAFrom, g.shaftBFrom);
+	});
+});
+
 describe("pickNearest (distance-check picking)", () => {
 	const nodes = [
 		{ id: "a", x: 10, y: 10 },