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>

src/AcDream.App/Input/LocalPlayerRuntimeState.cs

@@ -21,13 +21,74 @@ internal interface ILocalPlayerControllerSource
     PlayerMovementController? Controller { get; }
 }
 
+internal interface ILocalPlayerMotionSource
+{
+    MotionInterpreter? Motion { get; }
+}
+
 /// <summary>
 /// The one mutable local movement-controller slot. Player-mode lifecycle owns
 /// assignment; update and presentation owners receive the read-only seam.
 /// </summary>
-internal sealed class LocalPlayerControllerSlot : ILocalPlayerControllerSource
+internal sealed class LocalPlayerControllerSlot
+    : ILocalPlayerControllerSource,
+      ILocalPlayerMotionSource
 {
+    private PlayerMovementController? _preparingMotionOwner;
+
     public PlayerMovementController? Controller { get; set; }
+
+    /// <summary>
+    /// The motion owner visible to the local PartArray completion relay.
+    /// During player-mode construction this is the fully animation-bound
+    /// candidate controller; all other consumers continue to see only the
+    /// committed <see cref="Controller"/>.
+    /// </summary>
+    MotionInterpreter? ILocalPlayerMotionSource.Motion =>
+        _preparingMotionOwner?.Motion ?? Controller?.Motion;
+
+    /// <summary>
+    /// Opens the narrow construction-time ownership seam required by retail's
+    /// CPhysicsObj/PartArray lifetime. Initial placement synchronously queues
+    /// and completes StopCompletely, so its MotionDone relay must reach the
+    /// candidate interpreter before the complete controller is published.
+    /// </summary>
+    public IDisposable BeginMotionPreparation(PlayerMovementController controller)
+    {
+        ArgumentNullException.ThrowIfNull(controller);
+        if (_preparingMotionOwner is not null)
+        {
+            throw new InvalidOperationException(
+                "A local player motion owner is already being prepared.");
+        }
+
+        _preparingMotionOwner = controller;
+        return new MotionPreparation(this, controller);
+    }
+
+    private void EndMotionPreparation(PlayerMovementController controller)
+    {
+        if (!ReferenceEquals(_preparingMotionOwner, controller))
+        {
+            throw new InvalidOperationException(
+                "The local player motion preparation owner changed unexpectedly.");
+        }
+
+        _preparingMotionOwner = null;
+    }
+
+    private sealed class MotionPreparation(
+        LocalPlayerControllerSlot owner,
+        PlayerMovementController controller) : IDisposable
+    {
+        private LocalPlayerControllerSlot? _owner = owner;
+
+        public void Dispose()
+        {
+            LocalPlayerControllerSlot? current = Interlocked.Exchange(ref _owner, null);
+            current?.EndMotionPreparation(controller);
+        }
+    }
 }
 
 internal interface ILocalPlayerPhysicsHostSource

src/AcDream.App/Input/PlayerModeController.cs

@@ -386,6 +386,15 @@ internal sealed class PlayerModeController :
                     new MotionTableDispatchSink(sequencer);
             }
 
+            // Retail CPhysicsObj owns CMotionInterp and CPartArray throughout
+            // construction. Our split owners preserve that lifetime with a
+            // narrow preparation lease: SetPosition's synchronous type-5
+            // completion reaches this candidate MotionInterpreter, while the
+            // public controller slot remains unpublished until every other
+            // player-mode edge has prepared successfully.
+            using IDisposable motionPreparation =
+                _controllerSlot.BeginMotionPreparation(controller);
+
             ResolveResult initial = _physics.Resolve(
                 playerEntity.Position,
                 initialCellId,