Guard health sprite resolution

tests/assets.test.mjs

@@ -61,3 +61,44 @@ for (const [name, dataUrl] of Object.entries(alphaAssets)) {
     assert.ok(hasAlphaChunk || usesLosslessWebP, `${name} should preserve transparent background data`);
   });
 }
+
+const webpDimensions = (name, dataUrl) => {
+  const match = /^data:image\/webp;base64,([A-Za-z0-9+/=]+)$/.exec(dataUrl);
+  assert.ok(match, `${name} must be a WebP data URL`);
+  const bytes = Buffer.from(match[1], 'base64');
+
+  let offset = 12;
+  while (offset + 18 <= bytes.length) {
+    const type = bytes.subarray(offset, offset + 4).toString('ascii');
+    const size = bytes.readUInt32LE(offset + 4);
+    const dataOffset = offset + 8;
+
+    if (type === 'VP8X') {
+      const width =
+        1 +
+        bytes[dataOffset + 4] +
+        (bytes[dataOffset + 5] << 8) +
+        (bytes[dataOffset + 6] << 16);
+      const height =
+        1 +
+        bytes[dataOffset + 7] +
+        (bytes[dataOffset + 8] << 8) +
+        (bytes[dataOffset + 9] << 16);
+      return { width, height };
+    }
+
+    offset = dataOffset + size + (size % 2);
+  }
+
+  assert.fail(`${name} must expose VP8X dimensions`);
+};
+
+for (const [name, dataUrl] of Object.entries({ playerHealth, enemyHealth })) {
+  test(`${name} health sheet stays high resolution`, () => {
+    const { width, height } = webpDimensions(name, dataUrl);
+    assert.ok(width >= 1200, `${name} width must stay >= 1200px, got ${width}px`);
+    assert.ok(height >= 300, `${name} height must stay >= 300px, got ${height}px`);
+    assert.ok(width / 4 >= 300, `${name} frame width must stay >= 300px`);
+    assert.ok(height / 3 >= 100, `${name} frame height must stay >= 100px`);
+  });
+}