fix: stop drag-drop from reparenting item icons

Fixes #2793

Prevent Gwen's default drop handler from reparenting the dragged icon into the hovered control, which could place the icon into the wrong slot/container. Draggable now forwards DragAndDrop_HandleDrop to its SlotItem parent, and the drag package stores the source SlotItem in Package.UserData to make slot handlers deterministic.

Author: Arufonsu

Intersect.Client.Core/Interface/Game/Draggable.cs

@@ -16,6 +16,7 @@ public override bool DragAndDrop_Draggable()
 
     public override bool DragAndDrop_CanAcceptPackage(Package package)
     {
+        // Important: Icon is the topmost hovered control, so it must be allowed to "receive" the drop, BUT: we forward handling to SlotItem.
         return true;
     }
 
@@ -27,6 +28,7 @@ public override bool DragAndDrop_CanAcceptPackage(Package package)
             DrawControl = this,
             Name = Name,
             HoldOffset = ToLocal(InputHandler.MousePosition.X, InputHandler.MousePosition.Y),
+            UserData = Parent, // Expected to be SlotItem (InventoryItem/BankItem/etc)
         };
     }
 
@@ -39,4 +41,22 @@ public override void DragAndDrop_EndDragging(bool success, int x, int y)
     {
         IsVisibleInParent = true;
     }
+
+    public override bool DragAndDrop_HandleDrop(Package package, int x, int y)
+    {
+        // Never allow Base.DragAndDrop_HandleDrop() to run on the icon because it reparents SourceControl (Base.cs)
+        // Forward drop handling to the slot (or nearest SlotItem ancestor).
+        var node = Parent;
+        while (node != null)
+        {
+            if (node is SlotItem)
+            {
+                return node.DragAndDrop_HandleDrop(package, x, y);
+            }
+
+            node = node.Parent;
+        }
+
+        return false;
+    }
 }