Ignore hidden placeholder files in validator

validator.py

@@ -138,6 +138,13 @@ def _iter_data_refs(text: str) -> list[str]:
     return refs
 
 
+def _iter_visible_files(root: Path) -> set[Path]:
+    return {
+        path for path in root.rglob('*')
+        if path.is_file() and not any(part.startswith('.') for part in path.relative_to(root).parts)
+    }
+
+
 def cleanup_work_dir(work_dir: str | Path | None) -> None:
     if not work_dir:
         return
@@ -360,7 +367,7 @@ def validate_task_dir(
         if any(token in description for token in STALE_TOKENS):
             errors.append(f'{prefix}.description still contains stale source paths or legacy directories')
 
-    actual_data_files = {p for p in data_dir.rglob('*') if p.is_file()} if data_dir.exists() else set()
+    actual_data_files = _iter_visible_files(data_dir) if data_dir.exists() else set()
     uncovered = sorted(actual_data_files - covered_files)
     if uncovered:
         errors.append('data/ contains undeclared files: ' + ', '.join(rel(p, task_dir) for p in uncovered[:20]))
@@ -429,7 +436,7 @@ def validate_task_dir(
                     errors.append(f'{prefix}.path does not exist: {path_value}')
                 referenced_images.add(path_value)
 
-    actual_image_files = {str(p.relative_to(target_dir)) for p in images_dir.rglob('*') if p.is_file()} if images_dir.exists() else set()
+    actual_image_files = {str(p.relative_to(target_dir)) for p in _iter_visible_files(images_dir)} if images_dir.exists() else set()
     extra_images = sorted(actual_image_files - referenced_images)
     missing_images = sorted(referenced_images - actual_image_files)
     if extra_images: