fix: rule_signature conditions=None防御 + 0行表格覆盖率 + UT覆盖 - Closes #21

- step3 rule_signature: trigger.conditions=None 时使用 `or []` 防御
- step1 _quick_validate: total_rows=0 时行覆盖率设为 100% 而非 0%
- test_step1: 新增 TestHasSectionContent (10个) + TestQuickValidateEmptySections (2个)
- test_step3: 新增 TestRuleSignature (7个) + TestNormalizeRule (4个)

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

skills/ir_generation_skill/tests/test_step3.py

@@ -305,3 +305,163 @@ def test_step3_audit_report():
 if __name__ == "__main__":
     success = run_all_tests()
     sys.exit(0 if success else 1)
+
+
+# ═══════════════════════════════════════════════════════════════════════════════
+# Pure unit tests for step3 helper functions — no LLM output needed
+# ═══════════════════════════════════════════════════════════════════════════════
+
+from step3_merge_and_audit import rule_signature, _normalize_rule
+
+
+class TestRuleSignature:
+    """Unit tests for rule_signature with edge cases."""
+
+    def test_normal_rule(self):
+        """Standard rule with valid trigger dict should produce a signature."""
+        rule = {
+            "path": ["国内", "系统限制", "前台打断"],
+            "trigger": {
+                "operator": "AND",
+                "conditions": [
+                    {"signal": "车速", "operator": ">=", "value": "5"},
+                    {"signal": "档位", "operator": "==", "value": "D"}
+                ]
+            },
+            "actions": [
+                {"type": "system", "description": "弹出提示"}
+            ]
+        }
+        sig = rule_signature(rule)
+        assert isinstance(sig, str)
+        assert len(sig) == 16  # sha256 hex digest[:16]
+
+    def test_trigger_is_none(self):
+        """Rule with trigger: None should not crash."""
+        rule = {
+            "path": ["国内", "系统限制", "前台打断"],
+            "trigger": None,
+            "actions": [
+                {"type": "system", "description": "弹出提示"}
+            ]
+        }
+        sig = rule_signature(rule)
+        assert isinstance(sig, str)
+        assert len(sig) == 16
+
+    def test_trigger_key_missing(self):
+        """Rule without trigger key should not crash."""
+        rule = {
+            "path": ["国内", "系统限制"],
+            "actions": [
+                {"type": "system", "description": "限制启动"}
+            ]
+        }
+        sig = rule_signature(rule)
+        assert isinstance(sig, str)
+        assert len(sig) == 16
+
+    def test_actions_is_none(self):
+        """Rule with actions: None should not crash."""
+        rule = {
+            "path": ["国内"],
+            "trigger": {"conditions": []},
+            "actions": None
+        }
+        sig = rule_signature(rule)
+        assert isinstance(sig, str)
+        assert len(sig) == 16
+
+    def test_trigger_is_empty_dict(self):
+        """Rule with trigger: {} should work."""
+        rule = {
+            "path": ["海外", "SDK限制"],
+            "trigger": {},
+            "actions": []
+        }
+        sig = rule_signature(rule)
+        assert isinstance(sig, str)
+
+    def test_trigger_conditions_is_none(self):
+        """Rule with trigger.conditions: None should not crash."""
+        rule = {
+            "path": [],
+            "trigger": {"operator": "AND", "conditions": None},
+            "actions": [{"description": "do nothing"}]
+        }
+        # This might still crash if conditions is None because .get("conditions", [])
+        # returns None when the key exists with None value
+        # But our fix is on the trigger level, not conditions level
+        sig = rule_signature(rule)
+        assert isinstance(sig, str)
+
+    def test_deterministic_signature(self):
+        """Same rule should produce the same signature every time."""
+        rule = {
+            "path": ["国内", "系统限制", "前台打断"],
+            "trigger": {
+                "operator": "OR",
+                "conditions": [
+                    {"signal": "车速", "operator": ">", "value": "0"}
+                ]
+            },
+            "actions": [
+                {"description": "test"}
+            ]
+        }
+        sig1 = rule_signature(rule)
+        sig2 = rule_signature(rule)
+        assert sig1 == sig2
+
+
+class TestNormalizeRule:
+    """Unit tests for _normalize_rule."""
+
+    def test_normalize_null_trigger(self):
+        """_normalize_rule should fix trigger: None."""
+        rule = {"trigger": None, "actions": []}
+        normalized = _normalize_rule(rule)
+        # _normalize_rule fills in default trigger with conditions
+        assert "trigger" in normalized
+        assert normalized["trigger"]["operator"] == "AND"
+        assert len(normalized["trigger"]["conditions"]) >= 1
+        # After normalization, rule_signature should work
+        sig = rule_signature(normalized)
+        assert isinstance(sig, str)
+
+    def test_normalize_missing_trigger(self):
+        """_normalize_rule should add trigger if missing."""
+        rule = {"actions": []}
+        normalized = _normalize_rule(rule)
+        assert "trigger" in normalized
+        assert normalized["trigger"]["operator"] == "AND"
+        assert len(normalized["trigger"]["conditions"]) >= 1
+
+    def test_normalize_null_operator(self):
+        """_normalize_rule should fix null operator in conditions."""
+        rule = {
+            "trigger": {
+                "conditions": [
+                    {"signal": "车速", "operator": None, "value": "5"}
+                ]
+            },
+            "actions": []
+        }
+        normalized = _normalize_rule(rule)
+        cond = normalized["trigger"]["conditions"][0]
+        assert cond["operator"] == "=="
+
+    def test_normalize_keeps_valid_rule(self):
+        """_normalize_rule should not change a valid rule."""
+        rule = {
+            "trigger": {
+                "operator": "AND",
+                "conditions": [
+                    {"signal": "车速", "operator": ">=", "value": "5"}
+                ]
+            },
+            "actions": [{"type": "system", "description": "test"}]
+        }
+        normalized = _normalize_rule(rule)
+        assert normalized["trigger"]["operator"] == "AND"
+        assert normalized["trigger"]["conditions"][0]["operator"] == ">="