feat(engine): open drawElement fast capture to Windows hardware GPU

Widen the default-on drawElement clamp from darwin-only to darwin|win32
(still requiring a non-software-GPU browser). The darwin restriction was a
validation envelope, not an architectural limit — the CanvasDrawElement
Chrome flag ships on every platform, and every safety layer that made the
macOS default-on release (v0.7.38) survivable is platform-neutral:
compile-time gates, the SwiftShader init gate, per-render worker-encode
self-verification with screenshot fallback, and the blank guard. Worst case
on an unvalidated D3D11 backend is the same as on Metal: verify catches a
bad frame and the render re-runs on the screenshot baseline.

Why now: 30-day telemetry shows ~206k non-CI hardware-GPU Windows renders
(~78% of the win32 fleet, 18k installs) held on the slow screenshot path by
the clamp — the second-largest perf population after macOS, carrying ~1,550
capture-hours/month in the DE-eligible >=700-frame band alone at a measured
~2x speedup opportunity.

Instrumentation for the new cohort: drawElement session init now records the
raw WebGL UNMASKED_RENDERER_WEBGL string (detectSwiftShader generalized to
detectGpuBackend — same single evaluate, the string was previously read and
discarded) and threads it session -> CapturePerfSummary -> RenderPerfSummary
-> render_complete as `gpu_renderer`. drawElement damage proved
compositor-backend-specific throughout the macOS rollout, so D3D11-cohort
failures must cluster by ANGLE backend + GPU vendor (NVIDIA/AMD/Intel), not
just `os`.

The two DE clamp branches are extracted into a pure, unit-tested
`resolveDefaultDrawElement` (platform + GPU mode + worker-encode + explicit
opt-in), which also drops resolveConfig's cyclomatic complexity. The win32
streaming-encode compound tests collapse onto one shared helper.

Linux stays excluded: that fleet is headless/Docker SwiftShader, where DE
has no speedup and known rendering defects. Kill switches unchanged:
PRODUCER_EXPERIMENTAL_FAST_CAPTURE=false, --experimental-fast-capture=false.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

packages/cli/src/commands/render.ts

@@ -1102,7 +1102,6 @@ let deParallelRouterTrialFiredThisProcess = false;
  * resetting outside a test process where many independent test cases share
  * one imported module instance.
  */
-// fallow-ignore-next-line unused-export
 export function __resetDeParallelRouterTrialStateForTests(): void {
   deParallelRouterTrialManagedByUs = false;
   deParallelRouterTrialFiredThisProcess = false;
@@ -1429,6 +1428,7 @@ function trackRenderMetrics(
     deParallelRouter: perf?.drawElement?.parallelRouter,
     dePreRouterWorkers: perf?.drawElement?.preRouterWorkers,
     deGateReason: perf?.drawElement?.gateReason,
+    gpuRenderer: perf?.drawElement?.gpuRenderer,
     deWorkerEncode: perf?.drawElement?.workerEncode,
     deVerifyArmed: perf?.drawElement?.verifyArmed,
     deVerifyChecked: perf?.drawElement?.verifyChecked,

packages/cli/src/telemetry/events.ts

@@ -183,6 +183,8 @@ export function trackRenderComplete(
     deParallelRouter?: string;
     dePreRouterWorkers?: number;
     deGateReason?: string;
+    /** Raw WebGL renderer string from DE session init (ANGLE backend + GPU vendor). */
+    gpuRenderer?: string;
     deWorkerEncode?: boolean;
     deVerifyArmed?: number;
     deVerifyChecked?: number;
@@ -280,6 +282,7 @@ export function trackRenderComplete(
       de_parallel_router: props.deParallelRouter,
       de_pre_router_workers: props.dePreRouterWorkers,
       de_gate_reason: props.deGateReason,
+      gpu_renderer: props.gpuRenderer,
       de_worker_encode: props.deWorkerEncode,
       de_verify_armed: props.deVerifyArmed,
       de_verify_checked: props.deVerifyChecked,

packages/engine/src/config.test.ts

@@ -3,6 +3,7 @@ import { join } from "node:path";
 import { tmpdir } from "node:os";
 import {
   resolveConfig,
+  resolveDefaultDrawElement,
   DEFAULT_CONFIG,
   scaleProtocolTimeoutForComposition,
   shouldClampToScreenshotForConcreteGpu,
@@ -232,6 +233,40 @@ describe("resolveConfig", () => {
     });
   });
 
+  describe("resolveDefaultDrawElement (pure host clamp)", () => {
+    const base = {
+      useDrawElement: true,
+      explicitOptIn: false,
+      browserGpuMode: "hardware" as const,
+      workerEncode: true,
+    };
+    it("engages on darwin and win32, not linux", () => {
+      expect(resolveDefaultDrawElement({ ...base, platform: "darwin" })).toBe(true);
+      expect(resolveDefaultDrawElement({ ...base, platform: "win32" })).toBe(true);
+      expect(resolveDefaultDrawElement({ ...base, platform: "linux" })).toBe(false);
+    });
+    it("software GPU clamps off even on supported platforms", () => {
+      expect(
+        resolveDefaultDrawElement({ ...base, platform: "win32", browserGpuMode: "software" }),
+      ).toBe(false);
+    });
+    it("explicit opt-in overrides platform and GPU clamps", () => {
+      expect(
+        resolveDefaultDrawElement({
+          ...base,
+          explicitOptIn: true,
+          platform: "linux",
+          browserGpuMode: "software",
+        }),
+      ).toBe(true);
+    });
+    it("no worker-encode (no verify net) clamps the default off", () => {
+      expect(resolveDefaultDrawElement({ ...base, platform: "darwin", workerEncode: false })).toBe(
+        false,
+      );
+    });
+  });
+
   describe("useDrawElement (PRODUCER_EXPERIMENTAL_FAST_CAPTURE)", () => {
     it("default is clamped off on software-GPU hosts (page-side compositing preserved)", () => {
       setEnv("PRODUCER_BROWSER_GPU_MODE", "software");
@@ -242,21 +277,20 @@ describe("resolveConfig", () => {
       expect(config.enablePageSideCompositing).toBe(true);
     });
 
-    it("default engages on macOS with a hardware-GPU browser", () => {
-      setEnv("PRODUCER_BROWSER_GPU_MODE", "hardware");
-      unsetEnv("PRODUCER_EXPERIMENTAL_FAST_CAPTURE");
-      unsetEnv("HF_DE_WORKER_ENCODE");
-      const config = resolveConfig();
-      expect(config.useDrawElement).toBe(process.platform === "darwin");
-    });
-
-    it("default engages on macOS with auto GPU mode (the stock CLI path)", () => {
-      setEnv("PRODUCER_BROWSER_GPU_MODE", "auto");
-      unsetEnv("PRODUCER_EXPERIMENTAL_FAST_CAPTURE");
-      unsetEnv("HF_DE_WORKER_ENCODE");
-      const config = resolveConfig();
-      expect(config.useDrawElement).toBe(process.platform === "darwin");
-    });
+    // win32 opened 2026-07-27 (was darwin-only): ~206k non-CI hardware-GPU
+    // Windows renders / 30d sat on the screenshot path behind the old clamp.
+    // "auto" is the stock CLI path; both must pass the platform clamp.
+    for (const gpuMode of ["hardware", "auto"] as const) {
+      it(`default engages on macOS/Windows with ${gpuMode} GPU mode`, () => {
+        setEnv("PRODUCER_BROWSER_GPU_MODE", gpuMode);
+        unsetEnv("PRODUCER_EXPERIMENTAL_FAST_CAPTURE");
+        unsetEnv("HF_DE_WORKER_ENCODE");
+        const config = resolveConfig();
+        expect(config.useDrawElement).toBe(
+          process.platform === "darwin" || process.platform === "win32",
+        );
+      });
+    }
 
     it("default requires worker-encode (the verified drain)", () => {
       setEnv("PRODUCER_BROWSER_GPU_MODE", "hardware");
@@ -624,40 +658,58 @@ describe("resolveConfig", () => {
       Object.defineProperty(process, "platform", { value: originalPlatform, configurable: true });
     });
 
-    it("auto-disables on win32 + software-GPU + workers=1 + no user opt-in", () => {
-      setPlatform("win32");
-      setEnv("PRODUCER_BROWSER_GPU_MODE", "software");
-      setEnv("PRODUCER_MAX_WORKERS", "1");
+    /**
+     * Shared setup/assert for the win32 software-GPU compound: fixed common
+     * env (low-memory on, no explicit streaming opt-in), variable platform /
+     * gpu / workers, then assert whether the auto-disable fired.
+     */
+    function expectCompoundOutcome(opts: {
+      platform: NodeJS.Platform;
+      gpuMode?: string;
+      workers?: string;
+      autoDisabled: boolean;
+    }): void {
+      setPlatform(opts.platform);
+      if (opts.gpuMode === undefined) unsetEnv("PRODUCER_BROWSER_GPU_MODE");
+      else setEnv("PRODUCER_BROWSER_GPU_MODE", opts.gpuMode);
+      if (opts.workers === undefined) unsetEnv("PRODUCER_MAX_WORKERS");
+      else setEnv("PRODUCER_MAX_WORKERS", opts.workers);
       setEnv("PRODUCER_LOW_MEMORY_MODE", "true");
       unsetEnv("PRODUCER_ENABLE_STREAMING_ENCODE");
-
       const config = resolveConfig();
-      expect(config.enableStreamingEncode).toBe(false);
-      expect(config.streamingEncodeAutoDisabledOnWin32Compound).toBe(true);
+      expect(config.enableStreamingEncode).toBe(!opts.autoDisabled);
+      if (opts.autoDisabled) {
+        expect(config.streamingEncodeAutoDisabledOnWin32Compound).toBe(true);
+      } else {
+        expect(config.streamingEncodeAutoDisabledOnWin32Compound).toBeUndefined();
+      }
+    }
+
+    it("auto-disables on win32 + software-GPU + workers=1 + no user opt-in", () => {
+      expectCompoundOutcome({
+        platform: "win32",
+        gpuMode: "software",
+        workers: "1",
+        autoDisabled: true,
+      });
     });
 
     it("leaves streaming-encode on when platform is linux", () => {
-      setPlatform("linux");
-      setEnv("PRODUCER_BROWSER_GPU_MODE", "software");
-      setEnv("PRODUCER_MAX_WORKERS", "1");
-      setEnv("PRODUCER_LOW_MEMORY_MODE", "true");
-      unsetEnv("PRODUCER_ENABLE_STREAMING_ENCODE");
-
-      const config = resolveConfig();
-      expect(config.enableStreamingEncode).toBe(true);
-      expect(config.streamingEncodeAutoDisabledOnWin32Compound).toBeUndefined();
+      expectCompoundOutcome({
+        platform: "linux",
+        gpuMode: "software",
+        workers: "1",
+        autoDisabled: false,
+      });
     });
 
     it("leaves streaming-encode on when workers > 1", () => {
-      setPlatform("win32");
-      setEnv("PRODUCER_BROWSER_GPU_MODE", "software");
-      setEnv("PRODUCER_MAX_WORKERS", "4");
-      setEnv("PRODUCER_LOW_MEMORY_MODE", "true");
-      unsetEnv("PRODUCER_ENABLE_STREAMING_ENCODE");
-
-      const config = resolveConfig();
-      expect(config.enableStreamingEncode).toBe(true);
-      expect(config.streamingEncodeAutoDisabledOnWin32Compound).toBeUndefined();
+      expectCompoundOutcome({
+        platform: "win32",
+        gpuMode: "software",
+        workers: "4",
+        autoDisabled: false,
+      });
     });
 
     it("respects explicit env opt-in (PRODUCER_ENABLE_STREAMING_ENCODE=true) on the compound", () => {
@@ -703,16 +755,8 @@ describe("resolveConfig", () => {
       // --low-memory-mode implies screenshot capture. Compound applies even
       // if browserGpuMode is not literal "software" (defense-in-depth: matches
       // the OR semantics in `softwareGpuForced`).
-      setPlatform("win32");
-      unsetEnv("PRODUCER_BROWSER_GPU_MODE");
       unsetEnv("PRODUCER_DISABLE_GPU");
-      setEnv("PRODUCER_MAX_WORKERS", "1");
-      setEnv("PRODUCER_LOW_MEMORY_MODE", "true");
-      unsetEnv("PRODUCER_ENABLE_STREAMING_ENCODE");
-
-      const config = resolveConfig();
-      expect(config.enableStreamingEncode).toBe(false);
-      expect(config.streamingEncodeAutoDisabledOnWin32Compound).toBe(true);
+      expectCompoundOutcome({ platform: "win32", workers: "1", autoDisabled: true });
     });
 
     it("does not trigger when concurrency is 'auto' (workers not explicitly pinned)", () => {
@@ -720,15 +764,7 @@ describe("resolveConfig", () => {
       // helper's numeric workers check treats NaN as "unknown, don't trigger".
       // Downstream workers may still resolve to 1 via lowMemoryMode, but the
       // config-time clamp is deliberately conservative.
-      setPlatform("win32");
-      setEnv("PRODUCER_BROWSER_GPU_MODE", "software");
-      unsetEnv("PRODUCER_MAX_WORKERS");
-      setEnv("PRODUCER_LOW_MEMORY_MODE", "true");
-      unsetEnv("PRODUCER_ENABLE_STREAMING_ENCODE");
-
-      const config = resolveConfig();
-      expect(config.enableStreamingEncode).toBe(true);
-      expect(config.streamingEncodeAutoDisabledOnWin32Compound).toBeUndefined();
+      expectCompoundOutcome({ platform: "win32", gpuMode: "software", autoDisabled: false });
     });
   });
 

packages/engine/src/config.ts

@@ -66,8 +66,8 @@ export interface EngineConfig {
   /**
    * Use drawElementImage for frame capture (requires the CanvasDrawElement
    * Chrome flag, added globally in buildChromeArgs). Default ON, clamped in
-   * `resolveConfig` to hosts where it can actually engage (macOS + hardware-GPU
-   * browser); compile/init gates and the runtime self-verification net route
+   * `resolveConfig` to hosts where it can actually engage (macOS or Windows +
+   * hardware-GPU browser); compile/init gates and the runtime self-verification net route
    * incompatible or damaged renders back to screenshot capture.
    * Kill switch: `PRODUCER_EXPERIMENTAL_FAST_CAPTURE=false` (or the CLI
    * `--experimental-fast-capture=false`).
@@ -708,6 +708,39 @@ function memoryAdaptiveCacheBytesMb(): number {
  * Env vars provide backward compatibility during migration; explicit config
  * takes precedence over everything.
  */
+/**
+ * Platforms where default-on drawElement may engage: macOS (Metal-ANGLE,
+ * the original validated envelope) and Windows (D3D11-ANGLE, opened
+ * 2026-07-27 — see the clamp comment above resolveDefaultDrawElement's call
+ * site). Linux is excluded: that fleet is headless/Docker SwiftShader.
+ * Internal — the exported `resolveDefaultDrawElement` is the tested surface.
+ */
+function isDrawElementPlatform(platform: NodeJS.Platform): boolean {
+  return platform === "darwin" || platform === "win32";
+}
+
+/**
+ * Default-on drawElement host clamp. An explicit opt-in always wins (attempt
+ * DE, let the init-time gates route away — debugging relies on it). Otherwise
+ * DE stays on only where it can actually engage — a supported platform with a
+ * non-software-GPU browser — AND with worker-encode enabled: the runtime
+ * self-verification net lives in the worker-encode drain (the serial path has
+ * only the blank guard), so a default-on session without it would ship
+ * unverified drawElement frames. Pure; exported for tests.
+ */
+export function resolveDefaultDrawElement(args: {
+  useDrawElement: boolean;
+  explicitOptIn: boolean;
+  platform: NodeJS.Platform;
+  browserGpuMode: EngineConfig["browserGpuMode"];
+  workerEncode: boolean;
+}): boolean {
+  if (!args.useDrawElement) return false;
+  if (args.explicitOptIn) return true;
+  if (!isDrawElementPlatform(args.platform) || args.browserGpuMode === "software") return false;
+  return args.workerEncode;
+}
+
 export function resolveConfig(overrides?: Partial<EngineConfig>): EngineConfig {
   const env = (key: string): string | undefined => process.env[key];
   const envNum = (key: string, fallback: number): number => {
@@ -857,38 +890,45 @@ export function resolveConfig(overrides?: Partial<EngineConfig>): EngineConfig {
   };
 
   // Default-on drawElement is clamped to hosts where it can actually engage
-  // (macOS with a non-software-GPU browser; SwiftShader drops transparent
-  // sub-layers — crbug 521434899). "auto" passes the clamp: the stock CLI
-  // resolves GPU mode to auto, which probes to hardware on real Macs — and if
-  // it resolves to software after all, the SwiftShader init-time gate still
-  // routes the session to the screenshot baseline. Without the clamp, the
-  // default would needlessly disable page-side shader compositing (below) on
-  // Linux/Docker hosts where DE never runs. An EXPLICIT opt-in (env or caller override)
-  // skips the clamp and keeps the old semantics — attempt DE, let the
-  // init-time gates route away — which debugging relies on.
+  // (macOS or Windows with a non-software-GPU browser; SwiftShader drops
+  // transparent sub-layers — crbug 521434899). "auto" passes the clamp: the
+  // stock CLI resolves GPU mode to auto, which probes to hardware on real
+  // Macs/PCs — and if it resolves to software after all, the SwiftShader
+  // init-time gate still routes the session to the screenshot baseline.
+  // Without the clamp, the default would needlessly disable page-side shader
+  // compositing (below) on Linux/Docker hosts where DE never runs. An
+  // EXPLICIT opt-in (env or caller override) skips the clamp and keeps the
+  // old semantics — attempt DE, let the init-time gates route away — which
+  // debugging relies on.
+  //
+  // win32 opened 2026-07-27: telemetry showed ~206k non-CI hardware-GPU
+  // Windows renders / 30d (~78% of the win32 fleet) held on the slow
+  // screenshot path by the darwin-only clamp — the second-largest perf
+  // population after macOS. The mechanism is platform-neutral (the Chrome
+  // flag ships everywhere); darwin-only was a validation envelope, not an
+  // architectural limit. Opening it rides the same per-render safety
+  // contract macOS shipped with in v0.7.38: compile/init gates +
+  // worker-encode self-verify + screenshot fallback catch damage per
+  // render, and `gpu_renderer` telemetry (captured at DE session init)
+  // segments the D3D11/ANGLE cohort by GPU vendor so backend-specific
+  // damage clusters are attributable. Kill switches unchanged
+  // (PRODUCER_EXPERIMENTAL_FAST_CAPTURE=false; per-render --workers).
+  // Linux stays excluded: the fleet there is headless/Docker SwiftShader.
   const explicitDrawElementOptIn =
     env("PRODUCER_EXPERIMENTAL_FAST_CAPTURE") === "true" || overrides?.useDrawElement === true;
-  if (
-    merged.useDrawElement &&
-    !explicitDrawElementOptIn &&
-    !(process.platform === "darwin" && merged.browserGpuMode !== "software")
-  ) {
-    merged.useDrawElement = false;
-  }
-  // The runtime self-verification net lives in the worker-encode drain — the
-  // serial drawElement path has only the blank guard. Default-on drawElement
-  // therefore requires worker-encode; disabling HF_DE_WORKER_ENCODE without an
-  // explicit drawElement opt-in falls back to the screenshot baseline rather
-  // than shipping unverified drawElement frames.
-  if (merged.useDrawElement && !explicitDrawElementOptIn && !merged.enableDrawElementWorkerEncode) {
-    merged.useDrawElement = false;
-  }
+  merged.useDrawElement = resolveDefaultDrawElement({
+    useDrawElement: merged.useDrawElement,
+    explicitOptIn: explicitDrawElementOptIn,
+    platform: process.platform,
+    browserGpuMode: merged.browserGpuMode,
+    workerEncode: merged.enableDrawElementWorkerEncode,
+  });
 
   // Software GPU implies screenshot capture.
   //
   // Two existing platform gates already do most of the work: `browserManager`
   // only launches BeginFrame on Linux + chrome-headless-shell + !forceScreenshot,
-  // and the DE clamp above turns off `useDrawElement` on non-(darwin +
+  // and the DE clamp above turns off `useDrawElement` on non-((darwin|win32) +
   // non-software) hosts. Setting `forceScreenshot` here layers defense-in-depth
   // on top:
   //

packages/engine/src/services/drawElementService.test.ts

@@ -1,34 +1,49 @@
 import { describe, expect, it, vi } from "vitest";
 import type { Page } from "puppeteer-core";
-import { detectSwiftShader, resolveDrawElementCaptureMode } from "./drawElementService.js";
+import {
+  detectGpuBackend,
+  detectSwiftShader,
+  resolveDrawElementCaptureMode,
+} from "./drawElementService.js";
 
-// ── detectSwiftShader ──────────────────────────────────────────────────────────
+// ── detectGpuBackend / detectSwiftShader ───────────────────────────────────────
 
-describe("detectSwiftShader", () => {
+describe("detectGpuBackend", () => {
   function makePage(evaluateResult: unknown): Page {
     return {
       evaluate: vi.fn().mockResolvedValue(evaluateResult),
     } as unknown as Page;
   }
 
-  it("returns true when renderer includes 'swiftshader'", async () => {
-    const page = makePage(true);
+  it("carries the raw renderer string alongside the SwiftShader verdict", async () => {
+    const page = makePage({
+      isSwiftShader: false,
+      renderer: "ANGLE (NVIDIA, D3D11 vs_5_0 ps_5_0, D3D11)",
+    });
+    expect(await detectGpuBackend(page)).toEqual({
+      isSwiftShader: false,
+      renderer: "ANGLE (NVIDIA, D3D11 vs_5_0 ps_5_0, D3D11)",
+    });
+  });
+
+  it("reports null renderer when WebGL is unavailable", async () => {
+    const page = makePage({ isSwiftShader: false, renderer: null });
+    expect(await detectGpuBackend(page)).toEqual({ isSwiftShader: false, renderer: null });
+  });
+
+  it("detectSwiftShader wrapper returns true when renderer is SwiftShader", async () => {
+    const page = makePage({ isSwiftShader: true, renderer: "Google SwiftShader" });
     expect(await detectSwiftShader(page)).toBe(true);
   });
 
-  it("returns false for a standard GPU renderer string", async () => {
-    const page = makePage(false);
-    expect(await detectSwiftShader(page)).toBe(false);
-  });
-
-  it("returns false when WebGL is unavailable", async () => {
-    const page = makePage(false);
+  it("detectSwiftShader wrapper returns false for a hardware renderer", async () => {
+    const page = makePage({ isSwiftShader: false, renderer: "ANGLE (Apple, ANGLE Metal)" });
     expect(await detectSwiftShader(page)).toBe(false);
   });
 
   it("passes a function to page.evaluate", async () => {
-    const page = makePage(false);
-    await detectSwiftShader(page);
+    const page = makePage({ isSwiftShader: false, renderer: null });
+    await detectGpuBackend(page);
     expect(page.evaluate).toHaveBeenCalledWith(expect.any(Function));
   });
 });

packages/engine/src/services/drawElementService.ts

@@ -105,27 +105,50 @@ export function instrumentAcceleratedCanvases(): void {
   };
 }
 
+export interface GpuBackendInfo {
+  /** SwiftShader (software rasterizer) — e.g. Docker headless-shell. */
+  isSwiftShader: boolean;
+  /**
+   * Raw UNMASKED_RENDERER_WEBGL string (e.g. "ANGLE (Apple, ANGLE Metal
+   * Renderer: Apple M4 Pro, ...)", "ANGLE (NVIDIA, D3D11 ...)"), or null when
+   * WebGL / the debug extension is unavailable. Carried to render telemetry:
+   * drawElement failure modes proved compositor-backend-specific during the
+   * macOS rollout, so the win32/D3D11 cohort needs damage clusters
+   * attributable to a GPU vendor + ANGLE backend, not just `os`.
+   */
+  renderer: string | null;
+}
+
 /**
- * Detect whether the page is running on SwiftShader (software rasterizer).
+ * Detect the page's WebGL backend: SwiftShader vs a real GPU, plus the raw
+ * renderer string for telemetry.
  *
- * Returns true inside Docker headless-shell with --use-angle=swiftshader.
- * Returns false on macOS / Linux with a real GPU.
- * Call once after window.__hf is ready; cache result on session.
+ * `isSwiftShader` is true inside Docker headless-shell with
+ * --use-angle=swiftshader. Call once after window.__hf is ready; cache the
+ * result on the session.
  */
-export async function detectSwiftShader(page: Page): Promise<boolean> {
-  return page.evaluate(() => {
+export async function detectGpuBackend(page: Page): Promise<GpuBackendInfo> {
+  return page.evaluate((): GpuBackendInfo => {
     const canvas = document.createElement("canvas");
     const gl =
       canvas.getContext("webgl") ||
       (canvas.getContext("experimental-webgl") as WebGLRenderingContext | null);
-    if (!gl) return false;
+    if (!gl) return { isSwiftShader: false, renderer: null };
     const ext = gl.getExtension("WEBGL_debug_renderer_info");
-    if (!ext) return false;
+    if (!ext) return { isSwiftShader: false, renderer: null };
     const renderer = gl.getParameter(ext.UNMASKED_RENDERER_WEBGL) as string;
-    return renderer.toLowerCase().includes("swiftshader");
+    return { isSwiftShader: renderer.toLowerCase().includes("swiftshader"), renderer };
   });
 }
 
+/**
+ * Back-compat wrapper over {@link detectGpuBackend} for callers that only
+ * need the SwiftShader boolean.
+ */
+export async function detectSwiftShader(page: Page): Promise<boolean> {
+  return (await detectGpuBackend(page)).isSwiftShader;
+}
+
 /**
  * Inject a `<canvas layoutsubtree>` around the composition root.
  *

packages/engine/src/services/frameCapture.ts

@@ -34,7 +34,7 @@ import {
   shouldDefaultCaptureBeyondViewport,
 } from "./screenshotService.js";
 import {
-  detectSwiftShader,
+  detectGpuBackend,
   injectDrawElementCanvas,
   captureDrawElementFrame,
   resolveDrawElementCaptureMode,
@@ -146,6 +146,13 @@ export interface CaptureSession {
   config?: Partial<EngineConfig>;
   /** True if running on SwiftShader (detected at init). Undefined before init. */
   isSwiftShader?: boolean;
+  /**
+   * Raw WebGL UNMASKED_RENDERER_WEBGL string, captured alongside the
+   * SwiftShader probe at DE session init (e.g. "ANGLE (NVIDIA, D3D11 ...)").
+   * Surfaces in CapturePerfSummary → render telemetry so backend-specific
+   * drawElement damage (Metal vs D3D11 vs GL) clusters attributably.
+   */
+  gpuRenderer?: string;
   /** drawElementImage canvas was injected and is ready for capture. */
   drawElementReady?: boolean;
   /**
@@ -704,7 +711,9 @@ async function initDrawElementOrTransparentBackground(
     );
   }
   if (useDrawElement) {
-    session.isSwiftShader = await detectSwiftShader(page);
+    const gpuBackend = await detectGpuBackend(page);
+    session.isSwiftShader = gpuBackend.isSwiftShader;
+    session.gpuRenderer = gpuBackend.renderer ?? undefined;
     const transparent = session.options.format === "png";
     async function routeToFallback(): Promise<void> {
       session.captureMode = session.launchCaptureMode;
@@ -3784,6 +3793,7 @@ export function getCapturePerfSummary(session: CaptureSession): CapturePerfSumma
     beginFrameNoDamage: session.beginFrameNoDamageCount,
     beginFrameHasDamage: session.beginFrameHasDamageCount,
     captureMode: session.captureMode,
+    gpuRenderer: session.gpuRenderer,
     deGateReason: session.deGateReason,
     deFallbackTrigger: session.deFallbackTrigger,
     deWorkerEncode: session.workerEncodeEnabled ?? false,

packages/engine/src/types.ts

@@ -276,6 +276,14 @@ export interface CapturePerfSummary {
   // ── drawElement fast-capture outcome (default-on release visibility) ──
   /** Final capture mode this session used: "drawelement" | "screenshot" | "beginframe". */
   captureMode: string;
+  /**
+   * Raw WebGL UNMASKED_RENDERER_WEBGL string from DE session init (ANGLE
+   * backend + GPU vendor, e.g. "ANGLE (Apple, ANGLE Metal Renderer: ...)").
+   * Undefined when drawElement was never attempted. Lets telemetry cluster
+   * backend-specific damage now that DE engages on both Metal (darwin) and
+   * D3D11 (win32).
+   */
+  gpuRenderer?: string;
   /**
    * Low-cardinality init-time gate that routed a drawElement-eligible session
    * to the baseline: `swiftshader` | `css_effect:<fx>` | `at_risk_timeline` |

packages/producer/src/services/render/perfSummary.ts

@@ -111,6 +111,9 @@ function aggregateDrawElement(
   const gateReasons = [
     ...new Set(perfs.map((p) => p.deGateReason).filter((r): r is string => !!r)),
   ].sort();
+  const gpuRenderers = [
+    ...new Set(perfs.map((p) => p.gpuRenderer).filter((r): r is string => !!r)),
+  ].sort();
   const drain = de.drainStats;
   return {
     mode: modes.join("|") || "unknown",
@@ -121,6 +124,7 @@ function aggregateDrawElement(
     parallelRouter: de.parallelRouter ?? "none",
     preRouterWorkers: de.preRouterWorkers,
     gateReason: gateReasons.length > 0 ? gateReasons.join("|") : undefined,
+    gpuRenderer: gpuRenderers.length > 0 ? gpuRenderers.join("|") : undefined,
     workerEncode: perfs.some((p) => p.deWorkerEncode),
     verifyArmed: perfs.reduce((sum, p) => sum + (p.deVerifyArmed ?? 0), 0),
     verifyChecked: drain?.verifyChecked ?? 0,

packages/producer/src/services/renderOrchestrator.ts

@@ -498,6 +498,8 @@ export interface RenderPerfSummary {
     preRouterWorkers?: number;
     /** Engine init-time gate: swiftshader | css_effect:* | at_risk_timeline | 3d_init_failed | supersampling | render_mode_hint. */
     gateReason?: string;
+    /** Raw WebGL renderer string from DE session init (ANGLE backend + GPU vendor); |-joined across parallel sessions. */
+    gpuRenderer?: string;
     /** Worker-encode drain (the verified path) was active. */
     workerEncode: boolean;
     /** Self-verification ground-truth samples armed at init. */