Can only place item on grid top side

player/PickupController.cs

@@ -87,8 +87,16 @@ public partial class PickupController : Node3D
 		if (!_player.IsLocal) return;
 		EnsureCurrentItemValid();
 
+		static bool CanPlaceAgainst(Grid grid, Vector3 normal)
+		{
+			normal = grid.GlobalBasis.Inverse() * normal;
+			return normal.IsEqualApprox(Vector3.Up);
+		}
+
 		if (HasItemsHeld) {
 			if ((RayToMouseCursor() is RayResult ray) && (ray.Collider is Grid grid)
+					// Make sure this is placed against the top of the grid.
+					&& CanPlaceAgainst(grid, ray.Normal)
 					// Ensure item is not being added to itself or nested items.
 					&& !((grid.GetParent() == CurrentItem) || grid.ContainsItem(CurrentItem))) {
 				var transform = CurrentItem.GlobalTransform with { Origin = ray.Position };