diff --git a/Assets/Tests/EditMode/AI/AiRuntimeTests.cs b/Assets/Tests/EditMode/AI/AiRuntimeTests.cs
new file mode 100644
index 00000000..e00fdaaa
--- /dev/null
+++ b/Assets/Tests/EditMode/AI/AiRuntimeTests.cs
@@ -0,0 +1,93 @@
+using NUnit.Framework;
+using BaseGames.AI;
+
+namespace BaseGames.Tests.EditMode.AI
+{
+    public class AiRuntimeTests
+    {
+        static AiGraph Graph()
+        {
+            var b = new BrainBuilder();
+            b.Entry("Patrol");
+            b.Global().To("Dead").OnEvent(AiSignal.Died);
+            b.State("Patrol")
+                .Tick(c => c.Mover.WalkRandom())
+                .To("Chase").When(c => c.Sensor.SeesPlayer(), "SeesPlayer");
+            b.State("Chase")
+                .OnEnter(c => c.Mover.FacePlayer())
+                .Tick(c => c.Mover.MoveTo(c.Sensor.LastKnown))
+                .To("Search").When(c => c.Sensor.LostFor(2f), "LostFor(2s)");
+            b.State("Search")
+                .To("Patrol").After(3f);
+            b.State("Dead");
+            return b.Build();
+        }
+
+        [Test]
+        public void StartsAtEntry()
+        {
+            var rt = new AiRuntime(Graph(), new FakeAiContext());
+            Assert.AreEqual("Patrol", rt.CurrentStateName);
+        }
+
+        [Test]
+        public void Tick_RunsCurrentStateTickAction()
+        {
+            var ctx = new FakeAiContext();
+            var rt = new AiRuntime(Graph(), ctx);
+            rt.Tick(0.1f);
+            CollectionAssert.Contains(ctx.M.Calls, "WalkRandom");
+        }
+
+        [Test]
+        public void ConditionTransition_FiresAndRunsEnterExit()
+        {
+            var ctx = new FakeAiContext();
+            var rt = new AiRuntime(Graph(), ctx);
+            ctx.S.Sees = true;
+            rt.Tick(0.1f);
+            Assert.AreEqual("Chase", rt.CurrentStateName);
+            CollectionAssert.Contains(ctx.M.Calls, "FacePlayer"); // Chase.OnEnter
+        }
+
+        [Test]
+        public void Gate_SuspendsDecisionWhenNotControllable()
+        {
+            var ctx = new FakeAiContext();
+            var rt = new AiRuntime(Graph(), ctx);
+            ctx.S.Sees = true;
+            ctx.V.Controllable = false;   // 受击中
+            rt.Tick(0.1f);
+            Assert.AreEqual("Patrol", rt.CurrentStateName); // 未转换
+            Assert.IsTrue(rt.IsSuspended);
+            CollectionAssert.DoesNotContain(ctx.M.Calls, "WalkRandom"); // Tick 也不跑
+        }
+
+        [Test]
+        public void Gate_ResumesAndReevaluatesWhenControllable()
+        {
+            var ctx = new FakeAiContext();
+            var rt = new AiRuntime(Graph(), ctx);
+            ctx.S.Sees = true;
+            ctx.V.Controllable = false;
+            rt.Tick(0.1f);
+            ctx.V.Controllable = true;    // 恢复
+            rt.Tick(0.1f);
+            Assert.AreEqual("Chase", rt.CurrentStateName);
+        }
+
+        [Test]
+        public void After_UsesStateTimer()
+        {
+            var ctx = new FakeAiContext();
+            var rt = new AiRuntime(Graph(), ctx);
+            ctx.S.Sees = true; rt.Tick(0.1f);                 // -> Chase
+            ctx.S.Sees = false; ctx.S.LostForValue = 5f; rt.Tick(0.1f); // -> Search
+            Assert.AreEqual("Search", rt.CurrentStateName);
+            rt.Tick(1f); rt.Tick(1f);
+            Assert.AreEqual("Search", rt.CurrentStateName);   // 未满 3s
+            rt.Tick(1.5f);
+            Assert.AreEqual("Patrol", rt.CurrentStateName);   // 累计 >3s
+        }
+    }
+}
diff --git a/Assets/Tests/EditMode/AI/AiRuntimeTests.cs.meta b/Assets/Tests/EditMode/AI/AiRuntimeTests.cs.meta
new file mode 100644
index 00000000..c1523744
--- /dev/null
+++ b/Assets/Tests/EditMode/AI/AiRuntimeTests.cs.meta
@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: bf8b988fe76512c45aa8792dbbfc0ff6
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
diff --git a/Assets/Tests/EditMode/AI/Fakes.meta b/Assets/Tests/EditMode/AI/Fakes.meta
new file mode 100644
index 00000000..5311efce
--- /dev/null
+++ b/Assets/Tests/EditMode/AI/Fakes.meta
@@ -0,0 +1,8 @@
+fileFormatVersion: 2
+guid: 95728961a728dc349b73ada5def60ffa
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
diff --git a/Assets/Tests/EditMode/AI/Fakes/FakeAiContext.cs b/Assets/Tests/EditMode/AI/Fakes/FakeAiContext.cs
new file mode 100644
index 00000000..b47a5618
--- /dev/null
+++ b/Assets/Tests/EditMode/AI/Fakes/FakeAiContext.cs
@@ -0,0 +1,57 @@
+using System.Collections.Generic;
+using UnityEngine;
+using BaseGames.AI;
+
+namespace BaseGames.Tests.EditMode.AI
+{
+    public sealed class FakeSensor : ISensor
+    {
+        public bool Sees; public float LostForValue; public Vector2 Last;
+        public bool SeesPlayer() => Sees;
+        public bool InRange(float range) => Sees; // 简化：可见即在范围
+        public bool LostFor(float seconds) => LostForValue >= seconds;
+        public Vector2 LastKnown => Last;
+    }
+
+    public sealed class FakeMover : IMover
+    {
+        public List<string> Calls = new List<string>();
+        public void MoveTo(Vector2 t) => Calls.Add("MoveTo");
+        public void FacePlayer() => Calls.Add("FacePlayer");
+        public void Stop() => Calls.Add("Stop");
+        public void WalkRandom() => Calls.Add("WalkRandom");
+        public void LookAround() => Calls.Add("LookAround");
+    }
+
+    public sealed class FakeCombat : ICombatant
+    {
+        public string Running; public List<string> Used = new List<string>();
+        public bool UseAbility(string id) { Used.Add(id); Running = id; return true; }
+        public bool IsAbilityRunning(string id = null) => id == null ? Running != null : Running == id;
+        public bool NoAbilityRunning => Running == null;
+        public bool CanUseAbility(string id) => true;
+    }
+
+    public sealed class FakeVitals : IActorVitals
+    {
+        public bool Alive = true; public bool Controllable = true; public float Hp = 1f;
+        public bool IsAlive => Alive;
+        public bool IsControllable => Controllable;
+        public float HpPercent => Hp;
+        public bool HpBelow(float ratio) => Hp < ratio;
+    }
+
+    public sealed class FakeAiContext : IAiContext
+    {
+        public FakeSensor S = new FakeSensor();
+        public FakeMover M = new FakeMover();
+        public FakeCombat C = new FakeCombat();
+        public FakeVitals V = new FakeVitals();
+        public Blackboard BB = new Blackboard();
+        public ISensor Sensor => S;
+        public IMover Mover => M;
+        public ICombatant Combat => C;
+        public IActorVitals Vitals => V;
+        public Blackboard Blackboard => BB;
+    }
+}
diff --git a/Assets/Tests/EditMode/AI/Fakes/FakeAiContext.cs.meta b/Assets/Tests/EditMode/AI/Fakes/FakeAiContext.cs.meta
new file mode 100644
index 00000000..3f25f9e2
--- /dev/null
+++ b/Assets/Tests/EditMode/AI/Fakes/FakeAiContext.cs.meta
@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: 7ec131e6cb78fbb48bb85f7ebdcf9da7
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
diff --git a/Assets/_Game/Scripts/AI/AiRuntime.cs b/Assets/_Game/Scripts/AI/AiRuntime.cs
new file mode 100644
index 00000000..f4c822ea
--- /dev/null
+++ b/Assets/_Game/Scripts/AI/AiRuntime.cs
@@ -0,0 +1,107 @@
+using System.Collections.Generic;
+
+namespace BaseGames.AI
+{
+    /// <summary>
+    /// 每敌人实例一份的轻量执行器。持有当前状态、状态计时器、trace。
+    /// 共享的 AiGraph 不持有任何实例态。
+    /// </summary>
+    public sealed class AiRuntime
+    {
+        readonly AiGraph _graph;
+        readonly IAiContext _ctx;
+        AiState _current;
+        float _timeInState;
+
+        readonly Queue<AiSignal> _pending = new Queue<AiSignal>();
+        readonly List<TransitionRecord> _trace = new List<TransitionRecord>();
+        const int TraceCap = 16;
+
+        public AiRuntime(AiGraph graph, IAiContext ctx)
+        {
+            _graph = graph;
+            _ctx = ctx;
+            EnterInitial();
+        }
+
+        public string CurrentStateName => _current.Name;
+        public bool IsSuspended { get; private set; }
+        public IReadOnlyList<TransitionRecord> Trace => _trace;
+        public float TimeInStateValue => _timeInState;
+
+        void EnterInitial()
+        {
+            _current = _graph.GetState(_graph.EntryState);
+            _timeInState = 0f;
+            _current.OnEnter?.Invoke(_ctx);
+        }
+
+        /// <summary>供 BrainBuilder.After() 通过 context 读取当前 runtime 的状态计时器。</summary>
+        static readonly System.Runtime.CompilerServices.ConditionalWeakTable<IAiContext, AiRuntime> _byContext
+            = new System.Runtime.CompilerServices.ConditionalWeakTable<IAiContext, AiRuntime>();
+        internal static float TimeInState(IAiContext ctx)
+            => _byContext.TryGetValue(ctx, out var rt) ? rt._timeInState : 0f;
+
+        public void Tick(float dt)
+        {
+            _byContext.Remove(_ctx);
+            _byContext.Add(_ctx, this);
+
+            // IsControllable 让位门：受击/硬直/击飞时挂起，不推进决策也不跑 Tick。
+            if (!_ctx.Vitals.IsControllable)
+            {
+                IsSuspended = true;
+                return;
+            }
+            IsSuspended = false;
+
+            _timeInState += dt;
+
+            if (TryTransition())
+                return; // 本帧发生转换，新状态下一帧再 Tick
+
+            _current.OnTick?.Invoke(_ctx, dt);
+        }
+
+        bool TryTransition()
+        {
+            // 全局/父层转换优先（本任务只评估条件型；事件型在 Task 6 处理）
+            foreach (var t in _graph.GlobalTransitions)
+                if (!t.IsEvent && t.Condition(_ctx))
+                    return Switch(t);
+
+            foreach (var t in _current.Transitions)
+                if (!t.IsEvent && t.Condition(_ctx))
+                    return Switch(t);
+
+            return false;
+        }
+
+        bool Switch(Transition t)
+        {
+            var from = _current.Name;
+            _current.OnExit?.Invoke(_ctx);
+            _current = _graph.GetState(t.Target);
+            _timeInState = 0f;
+            RecordTrace(new TransitionRecord(from, t.Target, t.Label));
+            _current.OnEnter?.Invoke(_ctx);
+            return true;
+        }
+
+        void RecordTrace(TransitionRecord r)
+        {
+            _trace.Add(r);
+            if (_trace.Count > TraceCap) _trace.RemoveAt(0);
+        }
+
+        /// <summary>对象池复用时重置到初始态，清空所有实例态。</summary>
+        public void Reset()
+        {
+            _pending.Clear();
+            _trace.Clear();
+            _ctx.Blackboard.Clear();
+            IsSuspended = false;
+            EnterInitial();
+        }
+    }
+}
diff --git a/Assets/_Game/Scripts/AI/AiRuntime.cs.meta b/Assets/_Game/Scripts/AI/AiRuntime.cs.meta
new file mode 100644
index 00000000..b6ba09fe
--- /dev/null
+++ b/Assets/_Game/Scripts/AI/AiRuntime.cs.meta
@@ -0,0 +1,11 @@
+fileFormatVersion: 2
+guid: ee06ec9754397a84289448f7c76e384a
+MonoImporter:
+  externalObjects: {}
+  serializedVersion: 2
+  defaultReferences: []
+  executionOrder: 0
+  icon: {instanceID: 0}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 
diff --git a/Assets/_Game/Scripts/AI/BrainBuilder.cs b/Assets/_Game/Scripts/AI/BrainBuilder.cs
index 04269e24..6b754ed6 100644
--- a/Assets/_Game/Scripts/AI/BrainBuilder.cs
+++ b/Assets/_Game/Scripts/AI/BrainBuilder.cs
@@ -89,11 +89,12 @@ namespace BaseGames.AI
                 return _stateBuilder;
             }
 
-            /// <summary>在本状态停留 seconds 秒后转换（读 runtime 的状态计时器）。Task 5 回填实现。</summary>
+            /// <summary>在本状态停留 seconds 秒后转换（读 runtime 的状态计时器）。</summary>
             public StateBuilder After(float seconds)
             {
-                // 依赖 AiRuntime.TimeInState（Task 5 定义）。本任务先临时抛异常以通过编译，Task 5 回填正式实现。
-                throw new NotImplementedException("After 将在 Task 5 回填（依赖 AiRuntime 状态计时器）。");
+                _state.AddTransition(Transition.OnCondition(
+                    _target, c => AiRuntime.TimeInState(c) >= seconds, $"after {seconds}s"));
+                return _stateBuilder;
             }
         }