Recover sparse MAX sticker captures

worker/src/server.js

@@ -1452,9 +1452,81 @@ async function downloadDomStickerThroughScreenshot(p, request) {
       metrics.avgB > metrics.avgR + 45 &&
       metrics.avgG > metrics.avgR + 30;
   };
+  const stripMaxWallpaperFromStickerPng = async (buffer) => {
+    const base64 = buffer.toString("base64");
+    const strippedDataUrl = await p.evaluate(async (dataUrl) => {
+      const image = new Image();
+      image.src = dataUrl;
+      await image.decode();
+
+      const canvas = document.createElement("canvas");
+      canvas.width = image.naturalWidth;
+      canvas.height = image.naturalHeight;
+      const context = canvas.getContext("2d", { willReadFrequently: true });
+      if (!context || canvas.width <= 0 || canvas.height <= 0) {
+        return null;
+      }
+
+      context.drawImage(image, 0, 0);
+      const imageData = context.getImageData(0, 0, canvas.width, canvas.height);
+      const data = imageData.data;
+      let kept = 0;
+
+      for (let offset = 0; offset < data.length; offset += 4) {
+        const r = data[offset];
+        const g = data[offset + 1];
+        const b = data[offset + 2];
+        const a = data[offset + 3];
+        if (a <= 8) {
+          continue;
+        }
+
+        const looksLikeMaxWallpaper = b > r + 25 &&
+          g > r + 20 &&
+          b > 150 &&
+          g > 130;
+        if (looksLikeMaxWallpaper) {
+          data[offset + 3] = 0;
+          continue;
+        }
+
+        kept++;
+      }
+
+      if (kept < Math.max(80, Math.floor(canvas.width * canvas.height * 0.01))) {
+        return null;
+      }
+
+      context.putImageData(imageData, 0, 0);
+      return canvas.toDataURL("image/png");
+    }, `data:image/png;base64,${base64}`).catch(() => null);
+
+    const prefix = "data:image/png;base64,";
+    return typeof strippedDataUrl === "string" && strippedDataUrl.startsWith(prefix)
+      ? Buffer.from(strippedDataUrl.slice(prefix.length), "base64")
+      : null;
+  };
+  const hasMeaningfulStickerContent = (metrics) => {
+    if (!metrics) {
+      return false;
+    }
+
+    return metrics.opaqueRatio > 0.01 &&
+      (metrics.darkRatio > 0.01 ||
+        metrics.whiteRatio > 0.03 ||
+        metrics.cyanRatio < 0.5);
+  };
   const stickerCaptureResult = async (buffer) => {
     const metrics = await inspectStickerPng(buffer);
     if (isMaxWallpaperCapture(metrics)) {
+      const stripped = await stripMaxWallpaperFromStickerPng(buffer);
+      if (stripped) {
+        const strippedMetrics = await inspectStickerPng(stripped);
+        if (!isMaxWallpaperCapture(strippedMetrics) && hasMeaningfulStickerContent(strippedMetrics)) {
+          return { contentType: "image/png", buffer: stripped };
+        }
+      }
+
       throw new Error(`${kindLabel} capture matched MAX chat wallpaper instead of sticker.`);
     }