tested version with most of the final functionality. Still a few known issues, like dragging to a row that extends to multiple lines

row.cs

@@ -100,7 +100,6 @@ public partial class row : Control
 	}
     public void DropCardOn(Vector2 atPosition, Variant data)
     {
-		GD.Print($"Dropping at {atPosition}");
 		card c = data.As<card>()
 			?? throw new Exception("invalid drag data");
 		var g = this.GetParentOfType<game>()
@@ -131,7 +130,7 @@ public partial class row : Control
     }
 	public override bool _CanDropData(Vector2 atPosition, Variant data)
     {
-        return data.As<row>() is not null;
+        return data.Obj is row;
     }
     public override void _DropData(Vector2 atPosition, Variant data)
     {