forgot to push for a while, got drag-and-drop mostly working

UnassignedCardPanel.cs

@@ -0,0 +1,32 @@
+using Godot;
+using System;
+
+public partial class UnassignedCardPanel : PanelContainer
+{
+	// Called when the node enters the scene tree for the first time.
+	public override void _Ready()
+	{
+	}
+
+	// Called every frame. 'delta' is the elapsed time since the previous frame.
+	public override void _Process(double delta)
+	{
+	}
+	public override bool _CanDropData(Vector2 atPosition, Variant data)
+    {
+        return data.As<card>() is not null;
+    }
+    public override void _DropData(Vector2 atPosition, Variant data)
+    {
+		card c = data.As<card>()
+			?? throw new Exception("invalid drag data");
+		var g = this.GetParentOfType<game>()
+			?? throw new Exception("game instance not found");
+		if (g.ClaimCard(c.CardId) is card _c)
+		{
+			if (!ReferenceEquals(c, _c))
+				throw new Exception($"card move mismatch");
+			GetNode<HFlowContainer>("%UnassignedCardContainer").AddChild(c);
+		}
+    }
+}