fix: step3 _normalize_rule 处理 section 为 list 的 LLM 格式问题 - Closes #69

LLM 输出 section 字段有时为 list 而非 string，导致 .strip() 崩溃。
添加 _clean_section() 将 list→首元素 string，空 list 回退到 rule path。

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

skills/ir_generation_skill/step3_merge_and_audit.py

@@ -174,11 +174,25 @@ def _normalize_rule(rule: dict) -> dict:
     sources = rule.get("sources", [])
     valid_types = {"table", "text", "logic_tree"}
 
+    def _clean_section(val):
+        """Normalize section value: list→first element, ensure string."""
+        if isinstance(val, list):
+            return str(val[0]).strip() if val else ""
+        if isinstance(val, str):
+            return val.strip()
+        return str(val).strip() if val else ""
+
+    # Normalize section fields that might be lists (LLM format instability)
+    for s in sources:
+        sec = s.get("section")
+        if sec is not None:
+            s["section"] = _clean_section(sec)
+
     # try to infer a default section from the rule path
     default_section = ""
     for s in sources:
         sec = s.get("section", "")
-        if sec and sec.strip():
+        if sec and isinstance(sec, str) and sec.strip():
             default_section = sec.strip()
             break
     if not default_section: