diff --git a/xo-alloc2/src/gc/IGCObject_Any.cpp b/xo-alloc2/src/gc/IGCObject_Any.cpp
deleted file mode 100644
index 95c8cc84..00000000
--- a/xo-alloc2/src/gc/IGCObject_Any.cpp
+++ /dev/null
@@ -1,48 +0,0 @@
-/** @file IGCObject_Any.cpp
- *
- **/
-
-#include "detail/IGCObject_Any.hpp"
-#include <iostream>
-#include <exception>
-
-namespace xo {
-namespace mm {
-
-using xo::facet::DVariantPlaceholder;
-using xo::facet::typeseq;
-using xo::facet::valid_facet_implementation;
-
-void
-IGCObject_Any::_fatal()
-{
-    /* control here on uninitialized IAllocator_Any.
-     * Initialized instance will have specific implementation type
-     */
-    std::cerr << "fatal"
-              << ": attempt to call uninitialized"
-              << " IGCObject_Any method"
-              << std::endl;
-    std::terminate();
-}
-
-typeseq
-IGCObject_Any::s_typeseq = typeseq::id<DVariantPlaceholder>();
-
-bool
-IGCObject_Any::_valid
-  = valid_facet_implementation<AGCObject, IGCObject_Any>();
-
-// nonconst methods
-
-auto
-IGCObject_Any::forward_children(Opaque, obj<ACollector>)  const  noexcept -> size_type
-{
-    _fatal();
-}
-
-
-} /*namespace mm*/
-} /*namespace xo*/
-
-/* end IGCObject_Any.cpp */
diff --git a/xo-gc/include/xo/gc/MutationLogEntry.hpp b/xo-gc/include/xo/gc/MutationLogEntry.hpp
new file mode 100644
index 00000000..01c36660
--- /dev/null
+++ b/xo-gc/include/xo/gc/MutationLogEntry.hpp
@@ -0,0 +1,47 @@
+/** @file MutationLogEntry.hpp
+ *
+ *  @author Roland Conybeare, Mar 2026
+ **/
+
+#pragma once
+
+#include "GCObject.hpp"
+
+namespace xo {
+    namespace mm {
+
+        /** @brief Track a cross-generational pointer
+         *
+         *  GC must update pointer when collecting space that target occupies
+         *
+         *  Design notes:
+         *  - parent must be located at the beginning of an allocation,
+         *    (so that it's immediately preceded by allocation header)
+         *  - destination can be something like
+         *      obj<AGCObject>
+         *    but also something else such as
+         *      {obj<AType>, obj<ASyntaxStateMachine>, ..}
+         *  - for collector need to traverse data pointer *data
+         **/
+        class MutationLogEntry {
+        public:
+            MutationLogEntry(void * parent, void ** p_data, obj<AGCObject> snap);
+
+        private:
+            /** address of object containing logged mutation **/
+            void * parent_ = nullptr;
+            /** address of target member of object at address @ref parent_,
+             *  driving this log entry.
+             **/
+            void ** p_data_ = nullptr;
+            /** AGCObject i/face pointer, asof assignment responsible for this log entry.
+             *  If *p_data_ matches snap_.data(), then AGCObject interface is snap_.iface().
+             *  Otherwise log entry has been superseded by another assignment.
+             **/
+            obj<AGCObject> snap_;
+        };
+
+    } /*namespace mm*/
+} /*namespace xo*/
+
+/* end MutationLogEntry.hpp */