diff --git a/xo-alloc2/include/xo/alloc2/CollectorTypeRegistry.hpp b/xo-alloc2/include/xo/alloc2/CollectorTypeRegistry.hpp
index 2b3bd4b7..2515f486 100644
--- a/xo-alloc2/include/xo/alloc2/CollectorTypeRegistry.hpp
+++ b/xo-alloc2/include/xo/alloc2/CollectorTypeRegistry.hpp
@@ -12,6 +12,7 @@
 
 namespace xo {
     namespace mm {
+
         /** @class CollectorTypeRegistry
          *
          *  @brief Runtime registry for gc-aware types
@@ -68,7 +69,8 @@ namespace xo {
             /** initialization steps for a new Collector instance **/
             std::vector<init_function_type> init_seq_v_;
         };
-    }
-}
+
+    } /*namespace mm*/
+} /*namespace xo*/
 
 /* end CollectorTypeRegistry.hpp */
diff --git a/xo-alloc2/include/xo/alloc2/GCObjectConversion.hpp b/xo-alloc2/include/xo/alloc2/GCObjectConversion.hpp
index 59ec12fa..e7c06797 100644
--- a/xo-alloc2/include/xo/alloc2/GCObjectConversion.hpp
+++ b/xo-alloc2/include/xo/alloc2/GCObjectConversion.hpp
@@ -13,13 +13,27 @@
 
 namespace xo {
     namespace scm {
+        class GCObjectConversionUtil {
+        public:
+            using AGCObject = xo::mm::AGCObject;
+            using typeseq = xo::reflect::typeseq;
+
+            /** helper method fro GCObjectConversion<..>::from_gco()
+             *  on conversion failure
+             **/
+            static void _from_gco_fail_aux(obj<AGCObject> gco,
+                                           typeseq tseq,
+                                           scope * p_log);
+        };
+
         /** @brief compile-time conversion obj<AGCObject> <-> T
          *
          *  Specialize for each T that participates in conversion.
          *  Methods here aren't implemented
          **/
         template <typename T>
-        struct GCObjectConversion {
+        class GCObjectConversion {
+        public:
             using AGCObject = xo::mm::AGCObject;
             using AAllocator = xo::mm::AAllocator;
 
@@ -73,6 +87,13 @@ namespace xo {
                 }
             }
 
+            /** Several use cases here:
+             *  1. runtime polymorphism
+             *       obj<AGCObject,DArray> v(DArray::make(..));
+             *       // from_gco() doesn't know v repr
+             *       auto gc = GCObjectConversion<ASequence,DArray>::from_gco(mm, v);
+             *
+             **/
             static obj<AFacet,DRepr> from_gco(obj<AAllocator>,
                                               obj<AGCObject> gco) {
                 scope log(XO_DEBUG(false));
@@ -92,14 +113,10 @@ namespace xo {
                         auto retval = obj<AFacet,DRepr>::from(gco);
 
                         if (!retval) {
-                            log.retroactively_enable();
-
-                            log && log(xtag("gco.tseq", gco._typeseq()));
-                            log && log(xtag("DRepr.tseq", reflect::typeseq::id<DRepr>()));
+                            GCObjectConversionUtil::_from_gco_fail_aux
+                                (gco, reflect::typeseq::id<DRepr>(), &log);
                         }
 
-                        assert(retval);
-
                         return retval;
                     }
                 } else {
diff --git a/xo-alloc2/include/xo/alloc2/alloc/AAllocator.hpp b/xo-alloc2/include/xo/alloc2/alloc/AAllocator.hpp
index fdf57831..9d0966c7 100644
--- a/xo-alloc2/include/xo/alloc2/alloc/AAllocator.hpp
+++ b/xo-alloc2/include/xo/alloc2/alloc/AAllocator.hpp
@@ -64,6 +64,16 @@ namespace xo {
             /** @defgroup mm-allocator-methods Allocator methods **/
             ///@{
 
+            /** An uninitialized AAllocator instance will have zero vtable pointer
+             *  (per {linux,osx} abi).
+             *  Use case for this is narrow.
+             *  We go to some lengths to avoid null vtable pointers.
+             *  For example obj<AFacet> will have non-null vtable (via IFacet_Any)
+             *  with all methods terminating.
+             **/
+            bool _has_null_vptr() const noexcept {
+                return (*reinterpret_cast<const void * const *>(this) == nullptr);
+            }
             /** RTTI: unique id# for actual runtime data representation **/
             virtual typeseq _typeseq() const noexcept = 0;
             /** destroy instance @p d. Calls c++ destructor for actual runtime type.
diff --git a/xo-alloc2/include/xo/alloc2/alloc/RAllocator.hpp b/xo-alloc2/include/xo/alloc2/alloc/RAllocator.hpp
index f15dffca..b44d0a24 100644
--- a/xo-alloc2/include/xo/alloc2/alloc/RAllocator.hpp
+++ b/xo-alloc2/include/xo/alloc2/alloc/RAllocator.hpp
@@ -52,6 +52,7 @@ namespace xo {
                 return nullptr;
             }
 
+            bool    _has_null_vptr() const noexcept { return O::iface()->_has_null_vptr(); }
             typeseq       _typeseq() const noexcept { return O::iface()->_typeseq(); }
             void             _drop() const noexcept { O::iface()->_drop(O::data()); }
             std::string_view  name() const noexcept { return O::iface()->name(O::data()); }
diff --git a/xo-alloc2/include/xo/alloc2/alloc/RAllocator_aux.hpp b/xo-alloc2/include/xo/alloc2/alloc/RAllocator_aux.hpp
index c83a1dda..835b45fb 100644
--- a/xo-alloc2/include/xo/alloc2/alloc/RAllocator_aux.hpp
+++ b/xo-alloc2/include/xo/alloc2/alloc/RAllocator_aux.hpp
@@ -33,9 +33,14 @@ namespace xo {
                                            obj<AGCObject> * p_lhs,
                                            obj<AGCObject> rhs) noexcept
         {
-            this->barrier_assign_aux(parent,
-                                     p_lhs->iface(), p_lhs->opaque_data_addr(),
-                                     rhs.iface(), rhs.opaque_data());
+            if (this->data()) {
+                this->barrier_assign_aux(parent,
+                                         p_lhs->iface(), p_lhs->opaque_data_addr(),
+                                         rhs.iface(), rhs.opaque_data());
+            } else {
+                // special case: for null allocator want no write-barrier
+                *p_lhs = rhs;
+            }
         }
 
         template <typename Object>
@@ -48,11 +53,16 @@ namespace xo {
             // need to get AGCObject i/face that goes with DRepr.
             obj<AGCObject,DRepr> rhs_gco(rhs_data);
 
-            this->barrier_assign_aux(parent,
-                                     nullptr /*not needed*/,
-                                     lhs_data,
-                                     rhs_gco.iface(),
-                                     rhs_data);
+            if (this->data()) {
+                this->barrier_assign_aux(parent,
+                                         nullptr /*not needed*/,
+                                         lhs_data,
+                                         rhs_gco.iface(),
+                                         rhs_data);
+            } else {
+                // special case: for null allocator want no write-barrier
+                *lhs_data = rhs_data;
+            }
         }
 
     } /*namespace mm*/
diff --git a/xo-alloc2/src/alloc2/CMakeLists.txt b/xo-alloc2/src/alloc2/CMakeLists.txt
index 7929371a..8972e546 100644
--- a/xo-alloc2/src/alloc2/CMakeLists.txt
+++ b/xo-alloc2/src/alloc2/CMakeLists.txt
@@ -7,6 +7,7 @@ set(SELF_SRCS
     SetupAlloc2.cpp
 
     CollectorTypeRegistry.cpp
+    GCObjectConversion.cpp
 
     facet/ICollector_Any.cpp
 
diff --git a/xo-alloc2/src/alloc2/GCObjectConversion.cpp b/xo-alloc2/src/alloc2/GCObjectConversion.cpp
new file mode 100644
index 00000000..6df96b4b
--- /dev/null
+++ b/xo-alloc2/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 */
diff --git a/xo-alloc2/utest/CMakeLists.txt b/xo-alloc2/utest/CMakeLists.txt
index eacd19fd..33822241 100644
--- a/xo-alloc2/utest/CMakeLists.txt
+++ b/xo-alloc2/utest/CMakeLists.txt
@@ -9,6 +9,8 @@ set(UTEST_SRCS
     DArenaIterator.test.cpp
 #    Collector.test.cpp
 #    DX1CollectorIterator.test.cpp
+    Generation.test.cpp
+    dp.test.cpp
     random_allocs.cpp
 )
 
diff --git a/xo-alloc2/utest/Generation.test.cpp b/xo-alloc2/utest/Generation.test.cpp
new file mode 100644
index 00000000..43d64389
--- /dev/null
+++ b/xo-alloc2/utest/Generation.test.cpp
@@ -0,0 +1,42 @@
+/** @file Generation.test.cpp
+ *
+ *  @author Roland Conybeare, May 2026
+ **/
+
+#include "Generation.hpp"
+#include <catch2/catch.hpp>
+
+namespace xo {
+    using xo::mm::Generation;
+    using xo::mm::c_max_generation;
+
+    namespace ut {
+
+        TEST_CASE("Generation-1", "[Generation]")
+        {
+            REQUIRE(Generation::nursery() == 0);
+            REQUIRE(Generation::g0() == 0);
+            REQUIRE(Generation::g1() == 1);
+            REQUIRE(Generation::sentinel() == c_max_generation);
+
+            REQUIRE(Generation::g0().is_sentinel() == false);
+            REQUIRE(Generation::g1().is_sentinel() == false);
+            REQUIRE(Generation::sentinel().is_sentinel());
+
+            REQUIRE(Generation::g0() != Generation::sentinel());
+            REQUIRE(Generation::g1() != Generation::sentinel());
+
+            REQUIRE(!(Generation::g0() > Generation::g1()));
+            REQUIRE(Generation::g1() > Generation::g0());
+
+            auto g = Generation::g0();
+            ++g;
+            REQUIRE(g == Generation::g1());
+            ++g;
+            REQUIRE(g > Generation::g1());
+        }
+
+    } /*namespace ut*/
+} /*namespace xo*/
+
+/* end Generation.hpp */
diff --git a/xo-alloc2/utest/arena.test.cpp b/xo-alloc2/utest/arena.test.cpp
index 47ff4548..0beb66d8 100644
--- a/xo-alloc2/utest/arena.test.cpp
+++ b/xo-alloc2/utest/arena.test.cpp
@@ -3,11 +3,10 @@
  *  @author Roland Conybeare, Dec 2025
  **/
 
-#include "xo/alloc2/Allocator.hpp"
-#include "xo/alloc2/Arena.hpp"
-//#include "xo/alloc2/arena/IAllocator_DArena.hpp"
-#include "xo/arena/print.hpp"
-#include "xo/arena/padding.hpp"
+#include <xo/alloc2/Allocator.hpp>
+#include <xo/alloc2/Arena.hpp>
+#include <xo/arena/print.hpp>
+#include <xo/arena/padding.hpp>
 #include <xo/facet/obj.hpp>
 #include <xo/indentlog/scope.hpp>
 #include <catch2/catch.hpp>
@@ -150,7 +149,6 @@ namespace xo {
                               .size_ = 64*1024,
                               .debug_flag_ = false };
             DArena arena = DArena::map(cfg);
-            //obj<AAllocator, DArena> a1o{&arena};
             auto a1o = with_facet<AAllocator>::mkobj(&arena);
 
             REQUIRE(a1o.reserved() >= cfg.size_);
diff --git a/xo-alloc2/utest/dp.test.cpp b/xo-alloc2/utest/dp.test.cpp
new file mode 100644
index 00000000..e507b730
--- /dev/null
+++ b/xo-alloc2/utest/dp.test.cpp
@@ -0,0 +1,100 @@
+/** @file dp.test.cpp
+ *
+ *  @author Roland Conybeare, May 2026
+ **/
+
+#include "dp.hpp"
+#include <xo/alloc2/Allocator.hpp>
+#include <xo/alloc2/Arena.hpp>
+#include <catch2/catch.hpp>
+
+namespace xo {
+    using xo::mm::AAllocator;
+    using xo::mm::DArena;
+    using xo::mm::ArenaConfig;
+
+    namespace {
+        class Foo {
+        public:
+            explicit Foo(uint32_t * p_counter) : p_counter_{p_counter} {}
+
+            static constexpr bool is_gc_eligible() { return false; }
+
+            ~Foo() {
+                ++(*p_counter_);
+            }
+
+        private:
+            uint32_t * p_counter_ = nullptr;
+        };
+    }
+
+    namespace ut {
+
+        TEST_CASE("dp-1", "[dp]")
+        {
+            //ArenaConfig cfg { .name_ = "testarena", .size_ = 1024 };
+            //DArena arena = DArena::map(cfg);
+            //auto mm = obj<AAllocator,DArena>(&arena);
+
+            uint32_t counter = 0;
+            Foo foo(&counter);
+
+            REQUIRE(counter == 0);
+            {
+                dp<Foo> foo_dp(&foo);
+
+                REQUIRE(foo_dp);
+                REQUIRE(foo_dp.data());
+                REQUIRE(foo_dp.is_gc_eligible() == false);
+
+                // foo_dp dtor runs here, increments counter
+            }
+            REQUIRE(counter == 1);
+        }
+
+        TEST_CASE("dp-2", "[dp]")
+        {
+            uint32_t counter = 0;
+            Foo foo(&counter);
+
+            REQUIRE(counter == 0);
+            {
+                dp<Foo> foo_dp(&foo);
+
+                REQUIRE(foo_dp);
+                REQUIRE(foo_dp.data() == &foo);
+
+                foo_dp.release();
+
+                REQUIRE(!foo_dp);
+                REQUIRE(!foo_dp.data());
+
+                // foo_dp dtor runs here, increments counter
+            }
+            REQUIRE(counter == 0);
+        }
+
+        TEST_CASE("dp-DArena", "[dp][DArena]")
+        {
+            ArenaConfig cfg { .name_ = "testarena", .size_ = 1024 };
+            DArena arena = DArena::map(cfg);
+            //auto mm = obj<AAllocator,DArena>(&arena);
+
+            REQUIRE(arena.reserved() > 0);
+            REQUIRE(arena.is_mapped());
+            {
+                dp<DArena> arena_dp(&arena);
+
+                REQUIRE(arena_dp);
+                REQUIRE(arena_dp.data() == &arena);
+            }
+
+            REQUIRE(arena.reserved() == 0);
+            REQUIRE(!arena.is_mapped());
+        }
+
+    } /*namespace ut*/
+} /*namespace xo*/
+
+/* end dp.test.cpp */
diff --git a/xo-gc/include/xo/gc/DX1Collector.hpp b/xo-gc/include/xo/gc/DX1Collector.hpp
index e8b930fe..349fa51c 100644
--- a/xo-gc/include/xo/gc/DX1Collector.hpp
+++ b/xo-gc/include/xo/gc/DX1Collector.hpp
@@ -57,6 +57,24 @@ namespace xo {
             Generation gc_upto_;
         };
 
+        /** @class GcStatistics
+         **/
+        struct GCStatistics {
+        public:
+            GCStatistics() = default;
+            explicit GCStatistics(uint32_t n_gc) : n_gc_{n_gc} {};
+
+            uint32_t n_gc() const noexcept { return n_gc_; }
+
+            void include_gc() {
+                ++n_gc_;
+            }
+
+        private:
+            /** count #gc **/
+            uint32_t n_gc_ = 0;
+        };
+
         struct DX1CollectorIterator;
 
         /** @brief GC root struct
@@ -116,6 +134,8 @@ namespace xo {
 
             std::string_view name() const noexcept { return config_.name_; }
             GCRunState runstate() const noexcept { return runstate_; }
+            const GCStatistics & gc_stats() const noexcept { return gc_stats_; }
+
             const ObjectTypeTable * get_object_types() const noexcept { return gco_store_.get_object_types(); }
             const RootSet * get_root_set() const noexcept { return &root_set_; }
             const DArena * get_space(Role r, Generation g) const noexcept { return gco_store_.get_space(r, g); }
@@ -405,6 +425,9 @@ namespace xo {
              **/
             MutationLogStore mlog_store_;
 
+            /** counters collected across GC phases **/
+            GCStatistics gc_stats_;
+
             /** counters collected during @ref verify_ok call **/
             X1VerifyStats verify_stats_;
         };
diff --git a/xo-gc/src/gc/DX1Collector.cpp b/xo-gc/src/gc/DX1Collector.cpp
index 076f3480..7ea97982 100644
--- a/xo-gc/src/gc/DX1Collector.cpp
+++ b/xo-gc/src/gc/DX1Collector.cpp
@@ -528,6 +528,9 @@ namespace xo {
             log && log("step 5  : cleanup");
             this->_cleanup_phase(upto);
 
+            log && log("step 6  : update gc statistics");
+            gc_stats_.include_gc();
+
             if (config_.sanitize_flag_) {
                 log && log("step 5b : verify");
                 bool ok = this->verify_ok();
@@ -550,7 +553,7 @@ namespace xo {
         void
         DX1Collector::_swap_roles(Generation upto) noexcept
         {
-            scope log(XO_DEBUG(true), xtag("upto", upto));
+            scope log(XO_DEBUG(config_.debug_flag_), xtag("upto", upto));
 
             gco_store_.swap_roles(upto);
             mlog_store_.swap_roles(upto);
@@ -559,7 +562,7 @@ namespace xo {
         void
         DX1Collector::_cleanup_phase(Generation upto)
         {
-            scope log(XO_DEBUG(true), xtag("upto", upto));
+            scope log(XO_DEBUG(config_.debug_flag_), xtag("upto", upto));
 
             this->gco_store_.cleanup_phase(upto, config_.sanitize_flag_);
             this->runstate_ = GCRunState::idle();
@@ -568,7 +571,7 @@ namespace xo {
         void
         DX1Collector::_copy_roots(Generation upto) noexcept
         {
-            scope log(XO_DEBUG(true));
+            scope log(XO_DEBUG(config_.debug_flag_));
 
             for (RootSet::size_type i = 0, n = root_set_.size(); i < n; ++i) {
                 GCRoot & slot = root_set_[i];
diff --git a/xo-gc/src/gc/GCObjectStore.cpp b/xo-gc/src/gc/GCObjectStore.cpp
index fb29873e..c8eac5d6 100644
--- a/xo-gc/src/gc/GCObjectStore.cpp
+++ b/xo-gc/src/gc/GCObjectStore.cpp
@@ -705,7 +705,7 @@ namespace xo {
         void
         GCObjectStore::_verify_aux(AGCObject * iface, void * data)
         {
-            scope log(XO_DEBUG(config_.debug_flag_));
+            scope log(XO_DEBUG(false));
 
             (void)iface;
 
@@ -719,6 +719,7 @@ namespace xo {
                 if (!g2.is_sentinel()) {
                     // verify failure - live pointer still refers to from-space
 
+                    log.retroactively_enable();
                     print_backtrace_dwarf(true /*demangle*/);
 
                     ++(p_verify_stats_->n_from_);
@@ -1020,13 +1021,17 @@ namespace xo {
                                      AGCObject * iface,
                                      void * from_src)
         {
-            scope log(XO_DEBUG(config_.debug_flag_));
+            scope log(XO_DEBUG(config_.debug_flag_),
+                      xtag("iface", iface),
+                      xtag("from_src", from_src));
+
+            assert(!iface->_has_null_vptr());
 
             AllocInfo info = this->alloc_info((std::byte *)from_src);
 
             void * to_dest = iface->gco_shallow_move(from_src, gc);
 
-            log && log(xtag("from_src", from_src), xtag("to_dest", to_dest));
+            log && log(xtag("to_dest", to_dest));
             log && log(xtag("tseq", info.tseq()),
                        xtag("tname", TypeRegistry::id2name(typeseq(info.tseq()))),
                        xtag("age", info.age()),
diff --git a/xo-gc/src/gc/MutationLogStore.cpp b/xo-gc/src/gc/MutationLogStore.cpp
index 82a7d782..0719423a 100644
--- a/xo-gc/src/gc/MutationLogStore.cpp
+++ b/xo-gc/src/gc/MutationLogStore.cpp
@@ -160,8 +160,14 @@ namespace xo {
             assert(rhs_iface);
             assert(rhs_data);
 
-            if (lhs_iface)
-                *lhs_iface = *rhs_iface;
+            if (lhs_iface) {
+                // memcpy (not assignment): lhs_iface points to AGCObject storage
+                // whose vptr was set at construction (e.g. IGCObject_Any from
+                // a default-constructed obj<AGCObject>). Polymorphic copy-assignment
+                // copies AGCObject's data members but NOT the vptr, so it would
+                // leave the slot dispatching to the wrong (often fatal) iface.
+                ::memcpy((void *)lhs_iface, (void *)rhs_iface, sizeof(AGCObject));
+            }
 
             *lhs_addr = rhs_data;
 
@@ -195,6 +201,13 @@ namespace xo {
                 return;
             }
 
+            if (dest_g + 1 == config_.n_generation_) {
+                log && log(xtag("msg", "noop because dest in last gen"));
+
+                // don't need mlog entry to final gen
+                return;
+            }
+
             if (src_g < dest_g) {
                 log && log(xtag("msg", "noop because src gen younger than dest gen"));
 
@@ -259,7 +272,7 @@ namespace xo {
         void
         MutationLogStore::swap_roles(Generation upto) noexcept
         {
-            scope log(XO_DEBUG(true), xtag("upto", upto));
+            scope log(XO_DEBUG(config_.debug_flag_), xtag("upto", upto));
 
             for (Generation g = Generation{0}; g < upto; ++g) {
                 log && log("swap roles", xtag("g", g));
diff --git a/xo-gc/utest/CMakeLists.txt b/xo-gc/utest/CMakeLists.txt
index 4f555807..401371f6 100644
--- a/xo-gc/utest/CMakeLists.txt
+++ b/xo-gc/utest/CMakeLists.txt
@@ -9,6 +9,7 @@ set(UTEST_SRCS
     DX1CollectorIterator.test.cpp
     MutationLogStore.test.cpp
     GCObjectStore.test.cpp
+    GCObjectConversion.test.cpp
     Object2.test.cpp
 
     DMockCollector.cpp
diff --git a/xo-gc/utest/Collector.test.cpp b/xo-gc/utest/Collector.test.cpp
index 117f4ebb..ceb277b4 100644
--- a/xo-gc/utest/Collector.test.cpp
+++ b/xo-gc/utest/Collector.test.cpp
@@ -13,6 +13,7 @@
 #include <xo/object2/Array.hpp>
 #include <xo/object2/List.hpp>
 #include <xo/object2/Integer.hpp>
+#include <xo/alloc2/CollectorTypeRegistry.hpp>
 #include <xo/alloc2/Allocator.hpp>
 #include <xo/randomgen/xoshiro256.hpp>
 #include <xo/randomgen/random_seed.hpp>
@@ -25,6 +26,7 @@ namespace xo {
     using xo::scm::DList;
     using xo::scm::DArray;
     using xo::scm::DInteger;
+    using xo::mm::CollectorTypeRegistry;
     using xo::mm::AAllocator;
     using xo::mm::ACollector;
     using xo::mm::AGCObject;
@@ -33,9 +35,11 @@ namespace xo {
     using xo::mm::Role;
     using xo::mm::ArenaConfig;
     using xo::mm::AllocHeaderConfig;
+    using xo::mm::AllocHeader;
     using xo::mm::Generation;
     using xo::mm::c_max_generation;
     using xo::facet::with_facet;
+    using xo::reflect::typeseq;
     using xo::scope;
 
     namespace ut {
@@ -321,7 +325,11 @@ namespace xo {
                       .with_n_survive(tc.n_survive_)
                       .with_size(tc.gc_halfspace_z_)
                       .with_debug_flag(tc.debug_flag_))
-            {}
+            {
+                auto gc = obj<ACollector,DX1Collector>(&gc_);
+
+                CollectorTypeRegistry::instance().install_types(gc);
+            }
 
 #          define nil nullptr
 #          define T true
@@ -332,11 +340,11 @@ namespace xo {
                  *                     debug_flag
                  *               object_type_z  |
                  *        gc_halfspace_z     |  |
-                 *   n_survive         |     |  |
-                 *   n_gen   |         |     |  |
-                 *       v   v         v     v  v
+                 *  n_survive          |     |  |
+                 *   n_gen  |          |     |  |
+                 *       v  v          v     v  v
                  **/
-                Testcase(1, 2, 16 * 1024,  128, F),
+                Testcase(1, 2, 16 * 1024,  128, T),
             };
 
 #          undef T
@@ -345,10 +353,23 @@ namespace xo {
         } /*namespace*/
 
         // full collector test.
+        //
+        // PLAN:
+        // eventually: make generative
+        //
+        // Setup (
+        // 1. gc_utest_main.cpp Subsystem::initialize_all()
+        //    invokes per-module plugin init.  Gets types registered
+        //    with FacetRegistry, CollectorTypeRegistry etc.
+        // 2. per-utest collector setup (fixture)
+        //    calls CollectorTypeRegistry::instance().install_types(gc)
+        //    to establish the set of types that collector knows.
+        //
         TEST_CASE("collector-x1-gc", "[alloc2][gc]")
         {
-            scope log(XO_DEBUG(true),
-                      "DX1Collector gc test");
+            const auto & testname = Catch::getResultCapture().getCurrentTestName();
+
+            scope log(XO_DEBUG(true), xtag("test", testname));
 
             //std::uint64_t seed = 7988747704879432247ul;
             //random_seed(&seed);
@@ -372,7 +393,17 @@ namespace xo {
 
                 auto mm = x1.ref<AAllocator>();
                 auto gc = mm.to_facet<ACollector>();
-                Generation g1{1};
+
+                REQUIRE(mm._typeseq() == typeseq::id<DX1Collector>());
+                REQUIRE(gc._typeseq() == typeseq::id<DX1Collector>());
+
+                Generation g0 = Generation::g0();
+
+                REQUIRE(mm.allocated() == tc.object_type_z_);
+                REQUIRE(gc.allocated(g0, Role::to_space()) == 0);
+                REQUIRE(gc.allocated(g0, Role::from_space()) == 0);
+
+                Generation g1 = Generation::g1();
                 {
                     auto roots = DArray::_empty(mm, 1)->ref<AGCObject>();
                     REQUIRE(mm->contains_allocated(Role::to_space(), roots.data()));
@@ -383,12 +414,32 @@ namespace xo {
                         auto x1_gco = obj<AGCObject>(x1);
                         auto l1 = DList::cons(mm, x1, DList::_nil());
 
-#ifdef NOT_YET
-                        REQUIRE(roots->push_back(l1));
+                        REQUIRE(l1._typeseq() == typeseq::id<DList>());
+                        REQUIRE(roots->push_back(mm, l1));
                         REQUIRE(mm->contains_allocated(Role::to_space(), x1.data()));
                         REQUIRE(mm->contains_allocated(Role::to_space(), l1.data()));
 
-                        gc->add_gc_root_poly(&(*roots.operator->())[0]);
+                        REQUIRE(roots->at(0) == l1);
+                        REQUIRE(roots->at(0)._typeseq() == typeseq::id<DList>());
+
+                        // z: total allocated so far
+                        //   3x 8-byte header
+                        //   sizeof(DInteger)
+                        //   sizeof(DList)
+                        //   sizeof(DArray(1))
+                        //
+                        auto z = (3 * sizeof(AllocHeader)
+                                  + sizeof(DInteger)
+                                  + sizeof(DList)
+                                  + sizeof(DArray) + sizeof(obj<AGCObject>));
+                        {
+                            REQUIRE(z == 80);
+                            REQUIRE(mm.allocated() == tc.object_type_z_ + z);
+                            REQUIRE(gc.allocated(g0, Role::to_space()) == z);
+                            REQUIRE(gc.allocated(g1, Role::to_space()) == 0);
+                            REQUIRE(gc.allocated(g0, Role::from_space()) == 0);
+                            REQUIRE(gc.allocated(g1, Role::from_space()) == 0);
+                        }
 
                         gc->request_gc(g1);  // 1st GC
 
@@ -398,9 +449,20 @@ namespace xo {
                         // l1 target got moved, og locn now relabeled from-space
                         REQUIRE(mm->contains(Role::from_space(), l1.data()));
                         REQUIRE(!mm->contains_allocated(Role::from_space(), l1.data()));
-#endif
+
+                        REQUIRE(mm.allocated() == tc.object_type_z_ + z);
+                        REQUIRE(gc.allocated(g0, Role::to_space()) == z);
+                        REQUIRE(gc.allocated(g1, Role::to_space()) == 0);
+                        REQUIRE(gc.allocated(g0, Role::from_space()) == 0);
+                        REQUIRE(gc.allocated(g1, Role::from_space()) == 0);
                     }
+
+                    // NOTE: if this fails:
+                    //       look for preceding GCObjectStore::lookup_type out-of-bounds.
+                    //       May need to add to CollectorTypeRegistry
+                    //
                     REQUIRE(mm->contains_allocated(Role::to_space(), roots.data()));
+
                 }
             }
 
diff --git a/xo-gc/utest/GCObjectConversion.test.cpp b/xo-gc/utest/GCObjectConversion.test.cpp
new file mode 100644
index 00000000..1b094070
--- /dev/null
+++ b/xo-gc/utest/GCObjectConversion.test.cpp
@@ -0,0 +1,95 @@
+/** @file GCObjectConversion.test.cpp
+ *
+ *  @author Roland Conybeare, May 2026
+ **/
+
+#include "GCObjectConversion.hpp"
+#include <xo/object2/ListOps.hpp>
+#include <xo/object2/List.hpp>
+#include <xo/object2/Array.hpp>
+#include <xo/object2/Integer.hpp>
+#include <xo/alloc2/Arena.hpp>
+#include <catch2/catch.hpp>
+
+namespace xo {
+    //using xo::scm::ASequence;
+    using xo::scm::ListOps;
+    using xo::scm::DArray;
+    using xo::scm::DList;
+    using xo::scm::DInteger;
+    using xo::scm::GCObjectConversion;
+    using xo::mm::AGCObject;
+    using xo::mm::ArenaConfig;
+    using xo::mm::AAllocator;
+    using xo::mm::DArena;
+    using xo::facet::obj;
+
+    namespace ut {
+
+        TEST_CASE("GCObjectConversion-1", "[GCObjectConversion]")
+        {
+            scope log(XO_DEBUG(true), "GCObjectConversion-1");
+
+            ArenaConfig cfg {
+                .name_ = "testarena",
+                .size_ = 128
+            };
+            DArena arena = DArena::map(cfg);
+            auto mm = obj<AAllocator,DArena>(&arena);
+            auto v1 = DArray::empty(mm, 3);
+
+            REQUIRE(v1);
+            REQUIRE(v1->size() == 0);
+
+            {
+                obj v1_seq
+                    = GCObjectConversion<obj<AGCObject,DArray>>::from_gco(mm /*not used*/, v1);
+
+                REQUIRE(v1_seq);
+                REQUIRE(v1_seq == v1);
+                REQUIRE(v1_seq->size() == 0);
+            }
+
+            {
+                obj l1_seq
+                    = GCObjectConversion<obj<AGCObject,DList>>::from_gco(mm /*not used*/, v1);
+
+                REQUIRE(!l1_seq);
+            }
+        }
+
+        TEST_CASE("GCObjectConversion-2", "[GCObjectConversion]")
+        {
+            scope log(XO_DEBUG(true), "GCObjectConversion-2");
+
+            ArenaConfig cfg {
+                .name_ = "testarena",
+                .size_ = 128
+            };
+            DArena arena = DArena::map(cfg);
+            auto mm = obj<AAllocator,DArena>(&arena);
+            auto l1 = ListOps::cons(mm, DInteger::box(mm, 42), ListOps::nil());
+
+            REQUIRE(l1);
+            REQUIRE(l1->size() == 1);
+
+            {
+                // will fail; source is DArena
+                obj l1_seq
+                    = GCObjectConversion<obj<AGCObject,DList>>::from_gco(mm /*not used*/, l1);
+
+                REQUIRE(l1_seq);
+            }
+
+            {
+                obj v1_seq
+                    = GCObjectConversion<obj<AGCObject,DArray>>::from_gco(mm /*not used*/, l1);
+
+                REQUIRE(!v1_seq);
+            }
+        }
+
+    } /*namespace ut*/
+} /*namespace xo*/
+
+/* end GCObjectConversion.cpp */
diff --git a/xo-gc/utest/MutationLogStore.test.cpp b/xo-gc/utest/MutationLogStore.test.cpp
index 40e5f25e..f37ea67b 100644
--- a/xo-gc/utest/MutationLogStore.test.cpp
+++ b/xo-gc/utest/MutationLogStore.test.cpp
@@ -341,7 +341,7 @@ namespace ut {
             Testcase(2, 1, 16 * 1024, 8 * 128, T,   seq_2,  128, T,     c_fixed, 3,  0,  0,  0,  0, F),
             Testcase(2, 2, 16 * 1024, 8 * 128, T,   seq_3,  128, T,     c_fixed, 4,  0,  0,  0,  0, F),
             Testcase(2, 2, 16 * 1024, 8 * 128, T,   seq_4,  128, T,     c_fixed, 4,  0,  0,  0,  0, F),
-            Testcase(2, 2, 16 * 1024, 8 * 128, T,   seq_5,  128, T,     c_fixed, 4,  0,  0,  0,  0, T),
+            Testcase(2, 2, 16 * 1024, 8 * 128, T,   seq_5,  128, T,     c_fixed, 4,  0,  0,  0,  0, F),
         };
 
 #      undef T
diff --git a/xo-gc/utest/X1Collector.test.cpp b/xo-gc/utest/X1Collector.test.cpp
index 3bd4d4ee..421c4639 100644
--- a/xo-gc/utest/X1Collector.test.cpp
+++ b/xo-gc/utest/X1Collector.test.cpp
@@ -13,7 +13,6 @@
 #include <xo/object2/Float.hpp>
 #include <xo/object2/Integer.hpp>
 #include <xo/object2/List.hpp>
-//#include "list/IGCObject_DList.hpp"
 
 #include <xo/gc/X1Collector.hpp>
 //#include <xo/alloc2/Collector.hpp>
diff --git a/xo-object2/include/xo/object2/DArray.hpp b/xo-object2/include/xo/object2/DArray.hpp
index 64d7f52c..5f571333 100644
--- a/xo-object2/include/xo/object2/DArray.hpp
+++ b/xo-object2/include/xo/object2/DArray.hpp
@@ -76,6 +76,11 @@ namespace xo {
             static DArray * _empty(obj<AAllocator> mm,
                                    size_type cap);
 
+            /** ofp version of _empty(mm,cap) **/
+            template <typename AFacet = AGCObject>
+            static obj<AFacet,DArray> empty(obj<AAllocator> mm,
+                                            size_type cap);
+
             /** create copy of @p src using memory from @p mm
              *  with capacity for @p new_cap elements
              **/
@@ -198,6 +203,15 @@ namespace xo {
             ///@}
         };
 
+        template <typename AFacet>
+        obj<AFacet,DArray>
+        DArray::empty(obj<AAllocator> mm, DArray::size_type cap)
+        {
+            DArray * retval = _empty(mm, cap);
+
+            return obj<AFacet,DArray>(retval);
+        }
+
         template <typename... Args>
             requires (std::convertible_to<Args, obj<DArray::AGCObject>> && ...)
         DArray *
diff --git a/xo-object2/src/object2/DArray.cpp b/xo-object2/src/object2/DArray.cpp
index 2a5c590e..050f757d 100644
--- a/xo-object2/src/object2/DArray.cpp
+++ b/xo-object2/src/object2/DArray.cpp
@@ -84,7 +84,8 @@ namespace xo {
         }
 
         bool
-        DArray::push_back(obj<AAllocator> mm, obj<AGCObject> elt) noexcept
+        DArray::push_back(obj<AAllocator> mm,
+                          obj<AGCObject> elt) noexcept
         {
             if (size_ >= capacity_) {
                 return false;
diff --git a/xo-object2/utest/DArray.test.cpp b/xo-object2/utest/DArray.test.cpp
index 89353608..15da135e 100644
--- a/xo-object2/utest/DArray.test.cpp
+++ b/xo-object2/utest/DArray.test.cpp
@@ -63,6 +63,9 @@ namespace xo {
             auto alloc = with_facet<AAllocator>::mkobj(&arena);
             obj<AAllocator> null_mm;
 
+            REQUIRE(!null_mm.data());
+            REQUIRE(!null_mm._has_null_vptr()); // any
+
             DArray * arr = DArray::_empty(alloc, 16);
             REQUIRE(arr != nullptr);
             REQUIRE(arr->capacity() == 16);
diff --git a/xo-reader2/src/reader2/DDefineSsm.cpp b/xo-reader2/src/reader2/DDefineSsm.cpp
index 0e38f93d..59388820 100644
--- a/xo-reader2/src/reader2/DDefineSsm.cpp
+++ b/xo-reader2/src/reader2/DDefineSsm.cpp
@@ -466,7 +466,7 @@ namespace xo {
         DDefineSsm::on_parsed_typedescr(TypeDescr td,
                                         ParserStateMachine * p_psm)
         {
-            scope log(XO_DEBUG(true), xtag("td", td));
+            scope log(XO_DEBUG(p_psm->debug_flag()), xtag("td", td));
 
             if (defstate_ == defexprstatetype::def_3) {
                 this->defstate_ = defexprstatetype::def_4;