fix(generate_image): improve input image handling and validate output filename extensions

skills/nano-banana-pro-openrouter/scripts/generate_image.py

@@ -38,10 +38,10 @@ def parse_args():
       help="Output resolution: 1K, 2K, or 4K.",
     )
     parser.add_argument(
-        "--input-image",
-        action="append",
-        default=[],
-        help=f"Optional input image path (repeatable, max {MAX_INPUT_IMAGES}).",
+      "--input-image",
+      action="append",
+      default=[],
+      help=f"Optional input image path (repeatable, max {MAX_INPUT_IMAGES}).",
     )
     return parser.parse_args()
 
@@ -71,37 +71,44 @@ def build_message_content(prompt: str, input_images):
         content.append({"type": "image_url", "image_url": {"url": data_url}})
     return content
 
-    def parse_data_url(data_url: str):
-      if not data_url.startswith("data:") or ";base64," not in data_url:
+def parse_data_url(data_url: str):
+    if not data_url.startswith("data:") or ";base64," not in data_url:
         raise ValueError("Image URL is not a base64 data URL.")
-      header, encoded = data_url.split(",", 1)
-      mime = header[5:].split(";", 1)[0]
-      try:
+    header, encoded = data_url.split(",", 1)
+    mime = header[5:].split(";", 1)[0]
+    try:
         raw = base64.b64decode(encoded)
-      except Exception as e:
+    except Exception as e:
         raise SystemExit(f"Failed to decode base64 image payload: {e}")
-      return mime, raw
+    return mime, raw
 
 
 def resolve_output_paths(filename: str, image_count: int, mime: str):
-    output_path = Path(filename)
-    suffix = output_path.suffix
-    if not suffix:
-        suffix = MIME_TO_EXT.get(mime, ".png")
-        output_path = output_path.with_suffix(suffix)
+  output_path = Path(filename)
+  suffix = output_path.suffix
 
-    # Create parent directory if it doesn't exist (for absolute paths)
-    if output_path.parent and str(output_path.parent) != '.':
-        output_path.parent.mkdir(parents=True, exist_ok=True)
+  # Validate/correct suffix matches MIME type
+  expected_suffix = MIME_TO_EXT.get(mime, ".png")
+  if suffix and suffix.lower() != expected_suffix.lower():
+    print(f"Warning: filename extension '{suffix}' doesn't match returned MIME type '{mime}'. Using '{expected_suffix}' instead.")
+    suffix = expected_suffix
+  elif not suffix:
+    suffix = expected_suffix
 
-    if image_count == 1:
-        return [output_path]
+  output_path = output_path.with_suffix(suffix)
 
-    paths = []
-    for index in range(image_count):
-        numbered = output_path.with_name(f"{output_path.stem}-{index + 1}{suffix}")
-        paths.append(numbered)
-    return paths
+  # Create parent directory if it doesn't exist (for paths with parent directories, absolute or relative)
+  if output_path.parent and str(output_path.parent) != '.':
+    output_path.parent.mkdir(parents=True, exist_ok=True)
+
+  if image_count == 1:
+    return [output_path]
+
+  paths = []
+  for index in range(image_count):
+    numbered = output_path.with_name(f"{output_path.stem}-{index + 1}{suffix}")
+    paths.append(numbered)
+  return paths
 
 
 def extract_image_url(image):