Initial commit: OpenRA game engine

Fork from OpenRA/OpenRA with one-click launch script (start-ra.cmd)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

OpenRA.Game/Primitives/IObservableCollection.cs

@@ -0,0 +1,26 @@
+#region Copyright & License Information
+/*
+ * Copyright (c) The OpenRA Developers and Contributors
+ * This file is part of OpenRA, which is free software. It is made
+ * available to you under the terms of the GNU General Public License
+ * as published by the Free Software Foundation, either version 3 of
+ * the License, or (at your option) any later version. For more
+ * information, see COPYING.
+ */
+#endregion
+
+using System;
+using System.Collections;
+
+namespace OpenRA.Primitives
+{
+	public interface IObservableCollection
+	{
+		event Action<IObservableCollection, object> OnAdd;
+		event Action<IObservableCollection, object> OnRemove;
+		event Action<IObservableCollection, int> OnRemoveAt;
+		event Action<IObservableCollection, object, object> OnSet;
+		event Action<IObservableCollection> OnRefresh;
+		IEnumerable ObservedItems { get; }
+	}
+}