--- scaffold/normalize_tags.py
+++ final/normalize_tags.py
@@ -1,3 +1,10 @@
 def normalize_tags(tags):
-    """Scaffold only: requested normalization is deliberately absent."""
-    return tags
+    """Normalize string tags, retaining the first occurrence of each value."""
+    normalized = []
+    seen = set()
+    for tag in tags:
+        value = tag.strip().lower()
+        if value and value not in seen:
+            seen.add(value)
+            normalized.append(value)
+    return normalized
