Validate story image PNG color modes

scripts/verify-story-image-asset-data.mjs

@@ -9,6 +9,10 @@ const storyAssetsSourcePath = join('src', 'game', 'data', 'storyAssets.ts');
 
 const expectedStorySize = { width: 1672, height: 941 };
 const expectedPortraitSize = { width: 1254, height: 1254 };
+const allowedPngColorTypes = new Map([
+  [2, 'RGB'],
+  [6, 'RGBA']
+]);
 
 const server = await createServer({
   logLevel: 'error',
@@ -138,11 +142,17 @@ function validatePngFile(errors, path, expectedSize, label) {
 
   const width = bytes.readUInt32BE(16);
   const height = bytes.readUInt32BE(20);
+  const bitDepth = bytes[24];
+  const colorType = bytes[25];
   if (width !== expectedSize.width || height !== expectedSize.height) {
     errors.push(
       `${path}: ${label} should be ${expectedSize.width}x${expectedSize.height}, got ${width}x${height}`
     );
   }
+  if (bitDepth !== 8 || !allowedPngColorTypes.has(colorType)) {
+    const colorMode = allowedPngColorTypes.get(colorType) ?? `color type ${colorType}`;
+    errors.push(`${path}: ${label} should be 8-bit RGB/RGBA PNG, got ${bitDepth}-bit ${colorMode}`);
+  }
 }
 
 function validateRuntimeUrl(errors, key, url, path) {