fix(renderer): prevent stale SwiftShader layers

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

@@ -28,6 +28,25 @@ describe("buildChromeArgs browser GPU mode", () => {
     expect(args).not.toContain("--enable-gpu-rasterization");
   });
 
+  it("disables GPU compositing only for software BeginFrame capture", () => {
+    const softwareBeginFrame = buildChromeArgs(
+      { ...base, captureMode: "beginframe" },
+      { browserGpuMode: "software" },
+    );
+    const softwareScreenshot = buildChromeArgs(
+      { ...base, captureMode: "screenshot" },
+      { browserGpuMode: "software" },
+    );
+    const hardwareBeginFrame = buildChromeArgs(
+      { ...base, captureMode: "beginframe", platform: "linux" },
+      { browserGpuMode: "hardware" },
+    );
+
+    expect(softwareBeginFrame).toContain("--disable-gpu-compositing");
+    expect(softwareScreenshot).not.toContain("--disable-gpu-compositing");
+    expect(hardwareBeginFrame).not.toContain("--disable-gpu-compositing");
+  });
+
   it("uses Metal-backed ANGLE for hardware browser GPU mode on macOS", () => {
     const args = buildChromeArgs({ ...base, platform: "darwin" }, { browserGpuMode: "hardware" });
     expect(args).toContain("--enable-unsafe-webgpu");

packages/engine/src/services/browserManager.ts

@@ -686,6 +686,17 @@ export function buildChromeArgs(
 
   // BeginFrame flags — only when using chrome-headless-shell on Linux
   if (options.captureMode !== "screenshot") {
+    // SwiftShader's GPU compositor can retain a transformed layer for several
+    // sequential frames after a GSAP yoyo/reversal. The DOM and timeline are
+    // already at the requested time, but both BeginFrame and
+    // Page.captureScreenshot read the stale surface (the duplicate is present
+    // in the raw JPEG before encoding). Keep deterministic BeginFrame capture,
+    // but route compositing through Chrome's software path when the browser is
+    // already in software-GPU mode. Hardware-GPU and screenshot captures keep
+    // their existing compositor paths.
+    if (browserGpuMode === "software") {
+      chromeArgs.push("--disable-gpu-compositing");
+    }
     chromeArgs.push(
       "--deterministic-mode",
       "--enable-begin-frame-control",