Verify public canvas pixels

scripts/verify-public-deploy.mjs

@@ -48,15 +48,51 @@ try {
             width: canvas.width,
             height: canvas.height,
             clientWidth: canvas.clientWidth,
-            clientHeight: canvas.clientHeight
+            clientHeight: canvas.clientHeight,
+            pixelProbe: sampleCanvasPixels(canvas)
           }
         : undefined
     };
+
+    function sampleCanvasPixels(canvas) {
+      const context = canvas.getContext('2d', { willReadFrequently: true });
+      if (!context) {
+        return { readable: false, sampleCount: 0, nonTransparentRatio: 0, distinctColorBuckets: 0 };
+      }
+
+      const stepX = Math.max(1, Math.floor(canvas.width / 64));
+      const stepY = Math.max(1, Math.floor(canvas.height / 64));
+      const colorBuckets = new Set();
+      let sampleCount = 0;
+      let nonTransparentCount = 0;
+
+      for (let y = Math.floor(stepY / 2); y < canvas.height; y += stepY) {
+        for (let x = Math.floor(stepX / 2); x < canvas.width; x += stepX) {
+          const [r, g, b, a] = context.getImageData(x, y, 1, 1).data;
+          sampleCount += 1;
+          if (a > 8) {
+            nonTransparentCount += 1;
+          }
+          colorBuckets.add(`${r >> 4},${g >> 4},${b >> 4},${a >> 5}`);
+        }
+      }
+
+      return {
+        readable: true,
+        sampleCount,
+        nonTransparentRatio: sampleCount > 0 ? nonTransparentCount / sampleCount : 0,
+        distinctColorBuckets: colorBuckets.size
+      };
+    }
   });
 
   assert(state.title?.trim().length > 0, `Expected deployed page title: ${JSON.stringify(state)}`);
   assert(state.canvasCount === 1, `Expected exactly one game canvas: ${JSON.stringify(state)}`);
   assert(state.canvas?.width >= 960 && state.canvas?.height >= 540, `Expected desktop-size game canvas: ${JSON.stringify(state)}`);
+  assert(state.canvas?.pixelProbe?.readable === true, `Expected readable canvas pixels: ${JSON.stringify(state)}`);
+  assert(state.canvas.pixelProbe.sampleCount >= 500, `Expected enough canvas pixel samples: ${JSON.stringify(state)}`);
+  assert(state.canvas.pixelProbe.nonTransparentRatio > 0.5, `Expected non-empty canvas pixels: ${JSON.stringify(state)}`);
+  assert(state.canvas.pixelProbe.distinctColorBuckets >= 12, `Expected visually varied canvas pixels: ${JSON.stringify(state)}`);
 
   const relevantLogs = consoleMessages.filter(
     (message) => message.type === 'error' || (isWarning(message.type) && relevantLogPattern.test(message.text))