fix(search): review ambiguous topic assignments

tools/build_search_topic_taxonomy.py

@@ -57,7 +57,7 @@ def clean(value):
 def group_for(label):
     text = (label or "").casefold()
     matches = [code for code, pattern in RULES if re.search(pattern, text)]
-    return matches[0] if matches else "review_required"
+    return matches[0] if len(matches) == 1 else "review_required"
 
 
 def node_id(path):
@@ -121,8 +121,10 @@ def build(normalized_root):
         path = source_root / code / "document.json"
         try:
             data = json.loads(path.read_text(encoding="utf-8"))
-        except (OSError, json.JSONDecodeError):
-            return code, []
+        except (OSError, json.JSONDecodeError) as error:
+            raise RuntimeError(f"cannot read normalized document {code}: {error}") from error
+        if not isinstance(data, dict):
+            raise RuntimeError(f"normalized document {code} must contain a JSON object")
         return code, data.get("general_classifiers", [])
 
     with ThreadPoolExecutor(max_workers=24) as pool: