Let us start here, from square one. No, from Zero!

overlay/windows/wnd_manager.h

@@ -0,0 +1,19 @@
+#pragma once
+
+#include "overlay/window.h"
+
+namespace overlay::windows {
+
+    class WndManagerWindow : public Window {
+    public:
+
+        WndManagerWindow(SpiceOverlay *overlay);
+        ~WndManagerWindow() override;
+
+        void build_content() override;
+
+    private:
+
+        int window_current = -1;
+    };
+}