fix: step1 空章节过滤 + step3 rule_signature None-safe - Closes #21

- step1 _quick_validate 添加 _has_section_content() 过滤空内容章节
  (如仅含"无"字的图片章节)，避免误报低覆盖率警告
- step3 rule_signature 使用 `or {}` 防御 trigger=None 场景
  修复 QE 报告的 step3 AttributeError

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

skills/ir_generation_skill/step1_semantic_index.py

@@ -509,10 +509,28 @@ def _quick_validate(
             return True
         return True
 
+    def _has_section_content(sec: dict) -> bool:
+        """Check if a section has meaningful content (text >= 10 chars, table, or image).
+
+        A section is considered "empty" if all its text blocks have fewer than
+        10 characters and it contains no tables or images. These typically come
+        from image-only Word sections that doc_parser cannot extract text from.
+        """
+        for block in sec.get("blocks", []):
+            blk_type = block.get("type", "")
+            if blk_type == "table":
+                return True
+            if blk_type in ("image", "figure", "picture"):
+                return True
+            text = block.get("text", "")
+            if isinstance(text, str) and len(text.strip()) >= 10:
+                return True
+        return False
+
     func_sections = [
         s for s in doc.get("sections", [])
         if _is_functional_section(s.get("source", ""))
-        and any(b.get("type") in ("para", "table") for b in s.get("blocks", []))
+        and _has_section_content(s)
     ]
     covered_sections: set[str] = set()
     for fu in units:

skills/ir_generation_skill/step3_merge_and_audit.py

@@ -111,8 +111,8 @@ def load_path_enumeration() -> dict:
 def rule_signature(rule: dict) -> str:
     """Generate a dedup signature from path + trigger + actions."""
     path = rule.get("path", [])
-    trigger = rule.get("trigger", {})
-    actions = rule.get("actions", [])
+    trigger = rule.get("trigger") or {}
+    actions = rule.get("actions") or []
 
     conditions = sorted(
         trigger.get("conditions", []), key=lambda c: c.get("signal", "")