xo-interpreter2 stack: handle SequenceExpr + gc for frames

include/xo/expression2/SequenceExpr.hpp

@@ -0,0 +1,14 @@
+/** @file SequenceExpr.hpp
+ *
+ *  @author Roland Conybeare, Feb 2026
+ **/
+
+#pragma once
+
+#include "DSequenceExpr.hpp"
+#include "detail/IExpression_DSequenceExpr.hpp"
+#include "detail/IGCObject_DSequenceExpr.hpp"
+#include "detail/IPrintable_DSequenceExpr.hpp"
+
+/* end SequenceExpr.hpp */
+

src/expression2/DSequenceExpr.cpp

@@ -135,7 +135,7 @@ namespace xo {
 
             gc.forward_inplace(&iface, (void**)&expr_v_);
 
-            return shallow_size();
+            return this->shallow_size();
         }
 
     } /*namespace scm*/