fix: step3 过滤非法 source type + step1 重试质量门控 - Closes #57

- step3 _normalize_rule: 将 function_unit_description 等非法 source type 标准化为 text
- step1 覆盖反馈重试: 仅纳入实际提升覆盖率的 retry 结果，避免低质量输出稀释 ensemble
- 新增 UT: test_normalize_source_invalid_type

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

skills/ir_generation_skill/tests/test_step3.py

@@ -511,3 +511,18 @@ class TestNormalizeRule:
         }
         normalized = _normalize_rule(rule)
         assert "section" not in normalized["sources"][0]
+
+    def test_normalize_source_invalid_type(self):
+        """Invalid source types (LLM hallucinations) are normalized to text."""
+        rule = {
+            "trigger": {"conditions": [{"signal": "x", "operator": "==", "value": "1"}]},
+            "sources": [
+                {"type": "function_unit_description", "text_snippet": "desc",
+                 "section": "3.1 功能"},
+                {"type": "unknown_type", "text_snippet": "also invalid"},
+            ],
+        }
+        normalized = _normalize_rule(rule)
+        assert normalized["sources"][0]["type"] == "text"
+        assert normalized["sources"][1]["type"] == "text"
+        assert normalized["sources"][0]["section"] == "3.1 功能"