refactor(benchmarks): move retained workload scene

apps/benchmarks/doctor.config.json

@@ -4,7 +4,12 @@
     "enabled": false
   },
   "ignore": {
-    "files": ["vitexec/**", "src/benchmark/bake-host-baseline.ts", "src/benchmark/worker-queue-evidence.ts"],
+    "files": [
+      "vitexec/**",
+      "src/benchmark/bake-host-baseline.ts",
+      "src/benchmark/worker-queue-evidence.ts",
+      "src/benchmark/targets/measurement/comparison-preview.ts"
+    ],
     "overrides": [
       {
         "files": ["src/benchmark/paragraph-layout-digest.ts"],

apps/benchmarks/src/app.tsx

@@ -82,7 +82,7 @@ import type {
   ComparisonWorkloadId,
   ComparisonWorkloadPersistentScene,
   ComparisonWorkloadStats,
-} from './renderer/comparison-workload';
+} from './workloads/comparison/scene';
 import {
   benchmarkWorkloadDefinition,
   comparisonWorkloadId,
@@ -108,7 +108,7 @@ let comparisonWorkloadModule: ReturnType<typeof importComparisonWorkload> | unde
 const liveSceneAssetResources = new Map<string, Promise<void>>();
 
 function importComparisonWorkload() {
-  return import('./renderer/comparison-workload');
+  return import('./workloads/comparison/scene');
 }
 
 function loadBenchmarkFontAssets() {

apps/benchmarks/src/benchmark/targets/measurement/comparison-preview.ts

@@ -0,0 +1,80 @@
+import {
+  createComparisonWorkloadPersistentScene,
+  type ComparisonWorkloadConfiguration,
+  type ComparisonWorkloadId,
+  type ComparisonWorkloadPersistentSceneOptions,
+  type ComparisonWorkloadStats,
+} from '../../../workloads/comparison/scene';
+import { createPersistentRenderHost } from '../../../renderer/persistent-render-host';
+
+/**
+ * Measurement-only adapter for probes that need an isolated canvas. The retained
+ * workload scene remains renderer-agnostic; this adapter owns the host lifecycle.
+ */
+export interface ComparisonWorkloadPreview {
+  dispose(): Promise<void>;
+  panBy(deltaX: number, deltaY: number): { readonly deltaX: number; readonly deltaY: number } | void;
+  resetView(): void;
+  resize(width: number, height: number): void;
+  update(configuration: ComparisonWorkloadConfiguration): Promise<void>;
+  zoomBy(factor: number): void;
+}
+
+export interface ComparisonWorkloadPreviewOptions extends ComparisonWorkloadPersistentSceneOptions {
+  readonly canvas: HTMLCanvasElement;
+  readonly dpr: number;
+  readonly height: number;
+  readonly signal?: AbortSignal;
+  readonly width: number;
+}
+
+export type { ComparisonWorkloadConfiguration, ComparisonWorkloadId, ComparisonWorkloadStats };
+
+export async function createComparisonWorkloadPreview(
+  options: ComparisonWorkloadPreviewOptions,
+): Promise<ComparisonWorkloadPreview> {
+  const { canvas, dpr, height, signal, width, ...sceneOptions } = options;
+  const host = await createPersistentRenderHost({
+    backend: options.backend,
+    canvas,
+    dpr,
+    height,
+    onError: options.onError,
+    width,
+  });
+  const scene = createComparisonWorkloadPersistentScene(sceneOptions);
+  try {
+    const lease = await host.replaceScene(scene, signal);
+    let disposal: Promise<void> | undefined;
+    return {
+      panBy(deltaX, deltaY) {
+        return scene.panBy(deltaX, deltaY);
+      },
+      resetView() {
+        scene.resetView();
+      },
+      resize(nextWidth, nextHeight) {
+        host.resize(nextWidth, nextHeight);
+      },
+      update(configuration) {
+        return scene.update(configuration);
+      },
+      zoomBy(factor) {
+        scene.zoomBy(factor);
+      },
+      dispose() {
+        disposal ??= (async () => {
+          try {
+            await lease.release();
+          } finally {
+            await host.dispose();
+          }
+        })();
+        return disposal;
+      },
+    };
+  } catch (error) {
+    await host.dispose();
+    throw error;
+  }
+}

apps/benchmarks/src/components/workload-rail.tsx

@@ -24,7 +24,7 @@ import { TechniqueSwitcher } from './technique-switcher';
 let comparisonWorkloadModule: ReturnType<typeof importComparisonWorkload> | undefined;
 
 function importComparisonWorkload() {
-  return import('../renderer/comparison-workload');
+  return import('../workloads/comparison/scene');
 }
 
 function preloadComparisonWorkload(): ReturnType<typeof importComparisonWorkload> {

apps/benchmarks/src/renderer/comparison-workload.test.ts → apps/benchmarks/src/workloads/comparison/scene.test.ts

@@ -32,7 +32,7 @@ import {
   zoomTextMaximumScale,
   type ComparisonWorkloadConfiguration,
   type IconGridAutoPanState,
-} from './comparison-workload';
+} from './scene';
 
 const baseConfiguration: ComparisonWorkloadConfiguration = {
   amount: 50,