fix(ui): restore retail vitals and window interactions

tests/AcDream.App.Tests/UI/Layout/InventoryControllerTests.cs

@@ -1483,6 +1483,80 @@ public class InventoryControllerTests
             ctrl.OnDragOver(grid, grid.GetItem(0)!, Payload(0xFFFFu)));               // grid → green
     }
 
+    [Fact]
+    public void GroundPack_rejectsContentsGrid_butEmptyPackSlotAcceptsAndPicksUpAtThatSlot()
+    {
+        const uint droppedPack = 0x700000C0u;
+        var (layout, grid, containers, _, _, _, _, _) = BuildLayout();
+        var objects = new ClientObjectTable();
+        objects.AddOrUpdate(new ClientObject
+        {
+            ObjectId = Player,
+            Type = ItemType.Creature,
+            ItemsCapacity = 102,
+            ContainersCapacity = 7,
+        });
+        SeedBag(objects, 0x500000C1u, slot: 0);
+        SeedBag(objects, 0x500000C2u, slot: 1);
+        objects.AddOrUpdate(new ClientObject
+        {
+            ObjectId = droppedPack,
+            Name = "Dropped Pack",
+            Type = ItemType.Container,
+            ItemsCapacity = 24,
+        });
+        var puts = new List<(uint Item, uint Container, int Placement)>();
+        using var interaction = new ItemInteractionController(
+            objects,
+            new AcDream.Runtime.Gameplay.RuntimeInteractionTransactionState(
+                new InventoryTransactionState(objects)),
+            new InteractionState(),
+            playerGuid: () => Player,
+            sendUse: null,
+            sendUseWithTarget: null,
+            sendWield: null,
+            sendDrop: null,
+            groundObjectId: () => droppedPack,
+            backpackContainerId: () => Player,
+            placeInBackpack: static (_, _, _) => { });
+        using var controller = InventoryController.Bind(
+            layout,
+            objects,
+            () => Player,
+            iconIds: static (_, _, _, _, _) => 0u,
+            strength: () => 100,
+            selection: new SelectionState(),
+            datFont: null,
+            sendPutItemInContainer: (item, container, placement) =>
+                puts.Add((item, container, placement)),
+            itemInteraction: interaction);
+        var source = new UiItemSlot { SourceKind = ItemDragSource.Ground };
+        source.SetItem(droppedPack, 0u);
+        var payload = new ItemDragPayload(
+            droppedPack,
+            ItemDragSource.Ground,
+            SourceSlot: 0,
+            SourceCell: source);
+
+        Assert.Equal(
+            ItemDragAcceptance.Reject,
+            controller.OnDragOver(grid, grid.GetItem(0)!, payload));
+        controller.HandleDropRelease(grid, grid.GetItem(0)!, payload);
+        Assert.Empty(puts);
+
+        UiItemSlot emptyPackSlot = containers.GetItem(2)!;
+        Assert.Equal(0u, emptyPackSlot.ItemId);
+        Assert.Equal(
+            ItemDragAcceptance.Accept,
+            controller.OnDragOver(containers, emptyPackSlot, payload));
+        controller.HandleDropRelease(containers, emptyPackSlot, payload);
+
+        Assert.Equal(new[] { (droppedPack, Player, 2) }, puts);
+        Assert.True(interaction.TryGetPendingBackpackPlacement(droppedPack, out var pending));
+        Assert.Equal(Player, pending.ContainerId);
+        Assert.Equal(2, pending.Placement);
+    }
+
     [Fact]
     public void OnDragLift_selectsItem_butKeepsItUntilServerConfirms()
     {