xo-gc stack: fix mutation setup + xo-reader2 utest

src/alloc2/CMakeLists.txt

@@ -7,6 +7,7 @@ set(SELF_SRCS
     SetupAlloc2.cpp
 
     CollectorTypeRegistry.cpp
+    GCObjectConversion.cpp
 
     facet/ICollector_Any.cpp
 

src/alloc2/GCObjectConversion.cpp

@@ -0,0 +1,28 @@
+/** @file GCObjectConversion.cpp
+ *
+ *  @author Roland Conybeare, May 2026
+ **/
+
+#include "GCObjectConversion.hpp"
+
+namespace xo {
+    using xo::reflect::typeseq;
+
+    namespace scm {
+
+        void
+        GCObjectConversionUtil::_from_gco_fail_aux(obj<AGCObject> gco,
+                                                   typeseq tseq,
+                                                   scope * p_log)
+        {
+            p_log->retroactively_enable();
+            if (p_log) {
+                (*p_log)(xtag("gco.tseq", gco._typeseq()));
+                (*p_log)(xtag("DRepr.tseq", tseq));
+            }
+        }
+
+    } /*namespace scm*/
+} /*namespace xo*/
+
+/* end GCObjectConversion.cpp */