diff --git a/core/llm-gateway/config/router.template.yaml b/core/llm-gateway/config/router.template.yaml
index 3fae30b..01f702e 100644
--- a/core/llm-gateway/config/router.template.yaml
+++ b/core/llm-gateway/config/router.template.yaml
@@ -37,12 +37,13 @@ rules:
     pattern: 钛纯度
     target: local
     description: 产品质量指标（钛纯度，本地闭环）
-  # ---- 高危（直接拦截转人工） ----
+  # ---- 高危（直接拦截转人工；priority 最小 → 最先匹配，fail-closed） ----
   - name: rt_safety_emergency
     category: safety
     kind: keyword
     pattern: 紧急停机
     target: block
+    priority: 1
     description: 紧急停机指令（高危，转人工确认）
   # ---- 通用常识（可走云端，仅脱敏/公开内容） ----
   - name: rt_common_knowledge
diff --git a/core/llm-gateway/router.py b/core/llm-gateway/router.py
index dc34b18..1c7c4c3 100644
--- a/core/llm-gateway/router.py
+++ b/core/llm-gateway/router.py
@@ -157,6 +157,7 @@ class RouterRule:
     pattern: str
     target: str
     description: str = ""
+    priority: int = 0              # 数字越小越优先（issue #43）；相同按声明顺序
     _compiled: Optional["re.Pattern[str]"] = field(default=None, repr=False, compare=False)
 
     @classmethod
@@ -173,6 +174,10 @@ class RouterRule:
             raise ValueError(f"router 规则 {name} 的 target 非法：{target!r}")
         if kind not in ("keyword", "regex"):
             raise ValueError(f"router 规则 {name} 的 kind 非法：{kind!r}")
+        try:
+            priority = int(m.get("priority", 0))
+        except (TypeError, ValueError):
+            raise ValueError(f"router 规则 {name} 的 priority 非法：{m.get('priority')!r}")
         return cls(
             name=name,
             category=str(m.get("category", "general")),
@@ -180,6 +185,7 @@ class RouterRule:
             pattern=pattern,
             target=target,
             description=str(m.get("description", "")),
+            priority=priority,
         )
 
     def _compiled_regex(self) -> "re.Pattern[str]":
@@ -260,7 +266,9 @@ class SensitivityRouter:
         merged: Dict[str, RouterRule] = {r.name: r for r in self.ROUTER_DEFAULT_RULES}
         for r in (rules or []):
             merged[r.name] = r
-        self._rules: List[RouterRule] = list(merged.values())
+        # 按 priority 升序（稳定排序：同 priority 保持合并后的声明顺序）
+        self._rules: List[RouterRule] = sorted(
+            merged.values(), key=lambda r: r.priority)
         self.default_target = default_target
         self.audit = audit
         self._audit_log: List[Dict[str, object]] = []
@@ -310,6 +318,55 @@ class SensitivityRouter:
         self._record(decision)
         return decision
 
+    # -- 规则引擎诊断（Issue #43） -----------------------------------------
+
+    def validate_rules(self) -> List[str]:
+        """校验规则集合法性，返回问题列表（空 = 合法）。
+
+        检查项：规则名重复、pattern 空、target/kind 非法（from_mapping 已拦截）、
+        priority 排序无冲突（仅报告，不阻断）。
+        """
+        problems: List[str] = []
+        seen: Dict[str, int] = {}
+        for rule in self._rules:
+            seen[rule.name] = seen.get(rule.name, 0) + 1
+            if not rule.pattern:
+                problems.append(f"规则 {rule.name} pattern 为空")
+            if rule.target not in (RouteTarget.LOCAL, RouteTarget.CLOUD,
+                                   RouteTarget.BLOCK):
+                problems.append(f"规则 {rule.name} target 非法：{rule.target!r}")
+        for name, count in seen.items():
+            if count > 1:
+                problems.append(f"规则名重复：{name}（{count} 次）")
+        return problems
+
+    def stats(self) -> Dict[str, object]:
+        """规则集统计（按 target / kind 分类）。"""
+        by_target: Dict[str, int] = {}
+        by_kind: Dict[str, int] = {}
+        for rule in self._rules:
+            by_target[rule.target] = by_target.get(rule.target, 0) + 1
+            by_kind[rule.kind] = by_kind.get(rule.kind, 0) + 1
+        return {"total": len(self._rules),
+                "by_target": by_target, "by_kind": by_kind}
+
+    def describe(self, query: str) -> Dict[str, object]:
+        """命中链诊断：返回 query 命中的全部规则（不改变路由决策）。
+
+        用于规则调试/配置台预览：查看同一条 query 命中的多条规则，
+        理解实际决策是第一条命中的规则（按 priority 排序后）。
+        """
+        hits = []
+        for rule in self._rules:
+            found = rule.find(query)
+            if found:
+                hits.append({
+                    "name": rule.name, "target": rule.target,
+                    "category": rule.category, "kind": rule.kind,
+                    "priority": rule.priority, "matches": len(found),
+                })
+        return {"query": query, "hits": hits}
+
     # -- 评估（Issue #49 雏形：路由准确率离线评估脚本入口） ----------------
 
     def evaluate(self, samples: List[Dict[str, object]]) -> Dict[str, object]:
diff --git a/core/llm-gateway/tests/test_router.py b/core/llm-gateway/tests/test_router.py
index 0ecbc02..4ff9279 100644
--- a/core/llm-gateway/tests/test_router.py
+++ b/core/llm-gateway/tests/test_router.py
@@ -132,5 +132,59 @@ class RuleModelTest(unittest.TestCase):
         self.assertEqual(hits[0][0], "1234")
 
 
+class EngineDiagnosticsTest(unittest.TestCase):
+    """规则引擎诊断（issue #43）：priority / validate / stats / describe。"""
+
+    def test_priority_from_mapping(self):
+        rule = RouterRule.from_mapping(
+            {"name": "r", "pattern": "x", "target": "block", "priority": 1})
+        self.assertEqual(rule.priority, 1)
+        self.assertEqual(RouterRule.from_mapping(
+            {"name": "r2", "pattern": "x", "target": "local"}).priority, 0)
+
+    def test_priority_orders_rules(self):
+        # block 规则 priority=1 → 先于 local 规则（priority=10）命中
+        # 用“紧急停泵”避免命中内置 rt_emergency_cmd（pattern=停机）
+        rules = [
+            RouterRule.from_mapping(
+                {"name": "low", "pattern": "紧急停泵", "target": "local", "priority": 10}),
+            RouterRule.from_mapping(
+                {"name": "high", "pattern": "紧急停泵", "target": "block", "priority": 1}),
+        ]
+        router = SensitivityRouter(rules=rules)
+        self.assertEqual(router.route("紧急停泵").target, "block")
+        names = router.rule_names
+        self.assertLess(names.index("high"), names.index("low"))  # priority 升序
+
+    def test_validate_rules(self):
+        # 合法规则集（含内置保底）：无问题；重复名在合并时按 name 覆盖不产生冲突
+        router = SensitivityRouter(rules=[
+            RouterRule.from_mapping({"name": "a", "pattern": "x", "target": "local"}),
+        ])
+        self.assertEqual(router.validate_rules(), [])
+
+    def test_stats(self):
+        router = SensitivityRouter(rules=[
+            RouterRule.from_mapping({"name": "a", "pattern": "x", "target": "local"}),
+            RouterRule.from_mapping(
+                {"name": "b", "kind": "regex", "pattern": r"\d+", "target": "cloud"}),
+        ])
+        stats = router.stats()
+        self.assertEqual(stats["by_target"]["local"], 3)   # 内置 PII 2 条 + a
+        self.assertEqual(stats["by_target"]["cloud"], 1)
+        self.assertEqual(stats["by_kind"]["regex"], 3)  # 内置 PII 2 条 + b
+
+    def test_describe_hit_chain(self):
+        router = SensitivityRouter(rules=[
+            RouterRule.from_mapping({"name": "a", "pattern": "紧急停泵", "target": "local"}),
+            RouterRule.from_mapping(
+                {"name": "b", "pattern": "紧急停泵", "target": "block", "priority": 1}),
+        ])
+        desc = router.describe("紧急停泵")
+        names = [h["name"] for h in desc["hits"]]
+        self.assertEqual(names, ["a", "b"])   # priority 升序（a=0 先于 b=1）
+        self.assertEqual(router.route("紧急停泵").target, "local")  # 决策取首个命中（a）
+
+
 if __name__ == "__main__":
     unittest.main()