diff --git a/Assets/_Game/Scripts/AI/AiState.cs b/Assets/_Game/Scripts/AI/AiState.cs
index 20019f7e..b95bf287 100644
--- a/Assets/_Game/Scripts/AI/AiState.cs
+++ b/Assets/_Game/Scripts/AI/AiState.cs
@@ -6,11 +6,15 @@ namespace BaseGames.AI
     /// <summary>一个状态：进入/每帧/退出钩子 + 出边转换列表（按优先级有序，首个命中即转）。</summary>
     public sealed class AiState
     {
+        readonly List<Transition> _transitions = new List<Transition>();
+
         public string Name { get; }
         public Action<IAiContext> OnEnter { get; internal set; }
         public Action<IAiContext, float> OnTick { get; internal set; } // (ctx, dt)
         public Action<IAiContext> OnExit { get; internal set; }
-        public List<Transition> Transitions { get; } = new List<Transition>();
+        public IReadOnlyList<Transition> Transitions => _transitions;
+
+        internal void AddTransition(Transition t) => _transitions.Add(t);
 
         public AiState(string name) => Name = name;
     }
diff --git a/Assets/_Game/Scripts/AI/BrainBuilder.cs b/Assets/_Game/Scripts/AI/BrainBuilder.cs
index 0bc00d36..04269e24 100644
--- a/Assets/_Game/Scripts/AI/BrainBuilder.cs
+++ b/Assets/_Game/Scripts/AI/BrainBuilder.cs
@@ -61,17 +61,16 @@ namespace BaseGames.AI
             public StateBuilder Tick(Action<IAiContext, float> fn) { _state.OnTick = fn; return this; }
             public StateBuilder OnExit(Action<IAiContext> fn) { _state.OnExit = fn; return this; }
 
-            public TransitionBuilder To(string target) => new TransitionBuilder(_owner, this, _state, target);
+            public TransitionBuilder To(string target) => new TransitionBuilder(this, _state, target);
         }
 
         public sealed class TransitionBuilder
         {
-            readonly BrainBuilder _owner;
             readonly StateBuilder _stateBuilder;
             readonly AiState _state;
             readonly string _target;
-            internal TransitionBuilder(BrainBuilder owner, StateBuilder sb, AiState state, string target)
-            { _owner = owner; _stateBuilder = sb; _state = state; _target = target; }
+            internal TransitionBuilder(StateBuilder sb, AiState state, string target)
+            { _stateBuilder = sb; _state = state; _target = target; }
 
             /// <summary>
             /// 条件转换。label 为可读标签（用于 Mermaid 边 / trace 触发原因），
@@ -79,14 +78,14 @@ namespace BaseGames.AI
             /// </summary>
             public StateBuilder When(Func<IAiContext, bool> cond, string label = null)
             {
-                _state.Transitions.Add(Transition.OnCondition(_target, cond, label ?? "cond"));
+                _state.AddTransition(Transition.OnCondition(_target, cond, label ?? "cond"));
                 return _stateBuilder;
             }
 
             /// <summary>事件转换。</summary>
             public StateBuilder OnEvent(AiSignal evt)
             {
-                _state.Transitions.Add(Transition.OnEvent(_target, evt));
+                _state.AddTransition(Transition.OnEvent(_target, evt));
                 return _stateBuilder;
             }
 
@@ -108,12 +107,16 @@ namespace BaseGames.AI
 
             public GlobalBuilder OnEvent(AiSignal evt)
             {
+                if (_pendingTarget == null)
+                    throw new System.InvalidOperationException("Global(): 请先调用 To(target) 再 OnEvent/When。");
                 _owner.AddGlobal(Transition.OnEvent(_pendingTarget, evt));
                 return this;
             }
 
             public GlobalBuilder When(Func<IAiContext, bool> cond, string label = null)
             {
+                if (_pendingTarget == null)
+                    throw new System.InvalidOperationException("Global(): 请先调用 To(target) 再 OnEvent/When。");
                 _owner.AddGlobal(Transition.OnCondition(_pendingTarget, cond, label ?? "cond"));
                 return this;
             }