fix(cli): recapture snapshot composites after video injection

packages/cli/src/commands/snapshot.test.ts

@@ -31,6 +31,7 @@ import snapshotCommand, {
   computeSnapshotTimes,
   formatSnapshotTimestamp,
   parseZoomScale,
+  recaptureSnapshotComposite,
   requireSnapshotFfmpeg,
   resolveSnapshotVideoClipStart,
   resolveSnapshotVideoFrameTime,
@@ -475,3 +476,56 @@ describe("requireSnapshotFfmpeg", () => {
     expect(requireSnapshotFfmpeg("C:\\tools\\ffmpeg.exe")).toBe("C:\\tools\\ffmpeg.exe");
   });
 });
+
+describe("snapshot composite recapture", () => {
+  it.each([false, true])("recaptures only when a resolver exists: %s", async (hasResolver) => {
+    const order: string[] = [];
+    const runtimeWindow = {
+      __hf_page_composite_prepare: vi.fn(async () => {
+        order.push("prepare");
+        return true;
+      }),
+      __hf_page_composite_resolve: hasResolver
+        ? vi.fn(() => {
+            order.push("resolve");
+            return true;
+          })
+        : undefined,
+    };
+    vi.stubGlobal("window", runtimeWindow);
+    try {
+      await recaptureSnapshotComposite({
+        async evaluate<T>(callback: () => T): Promise<Awaited<T>> {
+          return await callback();
+        },
+        async screenshot(options) {
+          expect(options).toEqual({
+            type: "jpeg",
+            quality: 1,
+            clip: { x: 0, y: 0, width: 1, height: 1 },
+          });
+          order.push("paint");
+          return new Uint8Array();
+        },
+      });
+      expect(order).toEqual(hasResolver ? ["prepare", "paint", "resolve"] : []);
+    } finally {
+      vi.unstubAllGlobals();
+    }
+  });
+
+  it("places recapture after frame injection and visibility sync, before final capture", () => {
+    const source = readFileSync(new URL("./snapshot.ts", import.meta.url), "utf8");
+    const injection = source.indexOf("await injectVideoFramesBatch(page, updates)");
+    const visibility = source.indexOf("await syncVideoFrameVisibility(", injection);
+    const recapture = source.indexOf("await recaptureSnapshotComposite(page)", visibility);
+    const finalCapture = source.indexOf(
+      'page.screenshot({ path: framePath, type: "png"',
+      recapture,
+    );
+    expect(injection).toBeGreaterThan(-1);
+    expect(visibility).toBeGreaterThan(injection);
+    expect(recapture).toBeGreaterThan(visibility);
+    expect(finalCapture).toBeGreaterThan(recapture);
+  });
+});

packages/cli/src/commands/snapshot.ts

@@ -139,6 +139,43 @@ export function requireSnapshotFfmpeg(ffmpegPath: string | undefined): string {
   );
 }
 
+interface SnapshotCompositePage {
+  evaluate<T>(callback: () => T): Promise<Awaited<T>>;
+  screenshot(options: {
+    type: "jpeg";
+    quality: number;
+    clip: { x: number; y: number; width: number; height: number };
+  }): Promise<Uint8Array>;
+}
+
+/** Recapture canvas composites once the decoded video overlays have been injected. */
+export async function recaptureSnapshotComposite(page: SnapshotCompositePage): Promise<void> {
+  const hasPageComposite = await page.evaluate(async () => {
+    const runtimeWindow = window as Window & {
+      __hf_page_composite_prepare?: () => Promise<boolean>;
+      __hf_page_composite_resolve?: () => boolean;
+    };
+    if (typeof runtimeWindow.__hf_page_composite_resolve !== "function") return false;
+    await runtimeWindow.__hf_page_composite_prepare?.();
+    return true;
+  });
+  if (hasPageComposite) {
+    // The 1×1 screenshot forces Chrome to publish updated subtree paint records
+    // after injection, so resolve can consume them without a fixed delay.
+    await page.screenshot({
+      type: "jpeg",
+      quality: 1,
+      clip: { x: 0, y: 0, width: 1, height: 1 },
+    });
+    await page.evaluate(() => {
+      const runtimeWindow = window as Window & {
+        __hf_page_composite_resolve?: () => boolean;
+      };
+      runtimeWindow.__hf_page_composite_resolve?.();
+    });
+  }
+}
+
 /**
  * Extract a single frame from a video file at `timeSeconds` via FFmpeg.
  * Used to work around Chrome-headless's inability to reliably seek
@@ -595,6 +632,8 @@ async function captureSnapshots(
           }
         }
 
+        await recaptureSnapshotComposite(page);
+
         const timeLabel = formatSnapshotTimestamp(time);
         const index = String(i).padStart(2, "0");
         const filename = `frame-${index}-at-${timeLabel}.png`;