diff --git a/Assets/Tests/EditMode/AI/AiStateFragmentsTests.cs b/Assets/Tests/EditMode/AI/AiStateFragmentsTests.cs
index 2dcef846..a5c02489 100644
--- a/Assets/Tests/EditMode/AI/AiStateFragmentsTests.cs
+++ b/Assets/Tests/EditMode/AI/AiStateFragmentsTests.cs
@@ -114,5 +114,27 @@ namespace BaseGames.Tests.EditMode.AI
             var b = new BrainBuilder();
             Assert.Throws<System.ArgumentException>(() => AiStateFragments.AbilityOnce(b, "S", null));
         }
+
+        [Test]
+        public void Fragments_Throw_WhenTwoModulesDeclareSameState()
+        {
+            // 守卫存在的真正理由：两个独立模块取了同名状态时，
+            // 后者的回调会静默覆盖前者。经原语声明必须直接报错。
+            var b = new BrainBuilder();
+            AiStateFragments.Locomotion(b, "Idle", LocomotionMode.Idle);
+            var ex = Assert.Throws<System.InvalidOperationException>(
+                () => AiStateFragments.Locomotion(b, "Idle", LocomotionMode.Patrol));
+            StringAssert.Contains("Idle", ex.Message);
+        }
+
+        [Test]
+        public void Fragments_Throw_WhenDifferentFragmentKindsCollide()
+        {
+            // 跨层撞名同样要挡：未发现层的 Locomotion 态与死亡层的 Ability 态重名。
+            var b = new BrainBuilder();
+            AiStateFragments.Locomotion(b, "Shared", LocomotionMode.Patrol);
+            Assert.Throws<System.InvalidOperationException>(
+                () => AiStateFragments.Ability(b, "Shared", "atk"));
+        }
     }
 }
diff --git a/Assets/_Game/Scripts/AI/BrainBuilder.cs b/Assets/_Game/Scripts/AI/BrainBuilder.cs
index 860d6e21..948c5e3b 100644
--- a/Assets/_Game/Scripts/AI/BrainBuilder.cs
+++ b/Assets/_Game/Scripts/AI/BrainBuilder.cs
@@ -16,6 +16,10 @@ namespace BaseGames.AI
             return this;
         }
 
+        /// <summary>
+        /// 取一个状态，不存在则新建（宽松）。**只用于给别人已声明的态挂转换**。
+        /// 要声明一个态的行为（OnEnter/Tick/OnExit）请用 DeclareState()——它会挡住重名覆盖。
+        /// </summary>
         public StateBuilder State(string name)
         {
             if (!_states.TryGetValue(name, out var s))