fix(runtime): restore interaction completion ownership

Preserve prepublication local motion completion, require the PartArray enter-world lifecycle port, and balance deferred Use busy ownership across dispatch and cancellation. Reconcile the completed GameWindow connected gates and add regression coverage.

Co-authored-by: Codex <codex@openai.com>

tests/AcDream.App.Tests/Input/LocalPlayerControllerSlotTests.cs

@@ -0,0 +1,57 @@
+using AcDream.App.Input;
+using AcDream.Core.Physics;
+
+namespace AcDream.App.Tests.Input;
+
+public sealed class LocalPlayerControllerSlotTests
+{
+    [Fact]
+    public void MotionPreparation_RoutesCompletionWithoutPublishingController()
+    {
+        var slot = new LocalPlayerControllerSlot();
+        ILocalPlayerMotionSource source = slot;
+        var controller = new PlayerMovementController(new PhysicsEngine());
+        controller.Motion.AddToQueue(0, MotionCommand.Ready, 0);
+
+        using (slot.BeginMotionPreparation(controller))
+        {
+            Assert.Null(slot.Controller);
+            MotionInterpreter? owner = source.Motion;
+            Assert.Same(controller.Motion, owner);
+
+            owner!.MotionDone(MotionCommand.Ready, success: true);
+            Assert.False(controller.Motion.MotionsPending());
+        }
+
+        Assert.Null(source.Motion);
+    }
+
+    [Fact]
+    public void MotionPreparation_HandsOffToCommittedControllerOnDispose()
+    {
+        var slot = new LocalPlayerControllerSlot();
+        ILocalPlayerMotionSource source = slot;
+        var controller = new PlayerMovementController(new PhysicsEngine());
+
+        using (slot.BeginMotionPreparation(controller))
+        {
+            slot.Controller = controller;
+            Assert.Same(controller.Motion, source.Motion);
+        }
+
+        Assert.Same(controller.Motion, source.Motion);
+    }
+
+    [Fact]
+    public void MotionPreparation_RejectsConcurrentCandidate()
+    {
+        var slot = new LocalPlayerControllerSlot();
+        var first = new PlayerMovementController(new PhysicsEngine());
+        var second = new PlayerMovementController(new PhysicsEngine());
+
+        using IDisposable preparation = slot.BeginMotionPreparation(first);
+
+        Assert.Throws<InvalidOperationException>(
+            () => slot.BeginMotionPreparation(second));
+    }
+}