diff --git a/Makefile b/Makefile
index c26eccd1..6e9a5938 100644
--- a/Makefile
+++ b/Makefile
@@ -218,7 +218,7 @@ LDFLAGS += $(EXTRA_LDFLAGS)
 
 # Targets
 TARGET = test_hakmem
-OBJS_BASE = hakmem.o hakmem_config.o hakmem_tiny_config.o hakmem_ucb1.o hakmem_bigcache.o hakmem_pool.o hakmem_l25_pool.o hakmem_site_rules.o hakmem_tiny.o core/box/ss_allocation_box.o superslab_stats.o superslab_cache.o superslab_ace.o superslab_slab.o superslab_backend.o core/superslab_head_stub.o hakmem_smallmid.o tiny_sticky.o tiny_remote.o tiny_publish.o tiny_debug_ring.o hakmem_tiny_magazine.o hakmem_tiny_stats.o hakmem_tiny_sfc.o hakmem_tiny_query.o hakmem_tiny_rss.o hakmem_tiny_registry.o hakmem_tiny_remote_target.o hakmem_tiny_bg_spill.o tiny_adaptive_sizing.o hakmem_super_registry.o hakmem_shared_pool.o hakmem_shared_pool_acquire.o hakmem_shared_pool_release.o hakmem_elo.o hakmem_batch.o hakmem_p2.o hakmem_sizeclass_dist.o hakmem_evo.o hakmem_debug.o hakmem_sys.o hakmem_whale.o hakmem_policy.o hakmem_ace.o hakmem_ace_stats.o hakmem_prof.o hakmem_learner.o hakmem_size_hist.o hakmem_learn_log.o hakmem_syscall.o hakmem_ace_metrics.o hakmem_ace_ucb1.o hakmem_ace_controller.o tiny_fastcache.o core/box/superslab_expansion_box.o core/box/integrity_box.o core/box/free_publish_box.o core/box/mailbox_box.o core/box/front_gate_box.o core/box/front_gate_classifier.o core/box/capacity_box.o core/box/carve_push_box.o core/box/prewarm_box.o core/box/ss_hot_prewarm_box.o core/box/front_metrics_box.o core/box/bench_fast_box.o core/box/ss_addr_map_box.o core/box/slab_recycling_box.o core/box/pagefault_telemetry_box.o core/box/tiny_sizeclass_hist_box.o core/box/tiny_env_box.o core/box/tiny_route_box.o core/box/free_front_v3_env_box.o core/box/free_path_stats_box.o core/box/free_dispatch_stats_box.o core/box/alloc_gate_stats_box.o core/box/tiny_c6_ultra_free_box.o core/box/tiny_c5_ultra_free_box.o core/box/tiny_c4_ultra_free_box.o core/box/tiny_page_box.o core/box/tiny_class_policy_box.o core/box/tiny_class_stats_box.o core/box/tiny_policy_learner_box.o core/box/ss_budget_box.o core/box/tiny_mem_stats_box.o core/box/c7_meta_used_counter_box.o core/box/wrapper_env_box.o core/box/madvise_guard_box.o core/box/libm_reloc_guard_box.o core/box/ptr_trace_box.o core/box/link_missing_stubs.o core/box/super_reg_box.o core/box/shared_pool_box.o core/box/remote_side_box.o core/page_arena.o core/front/tiny_unified_cache.o core/tiny_alloc_fast_push.o core/tiny_c7_ultra_segment.o core/tiny_c7_ultra.o core/link_stubs.o core/tiny_failfast.o core/tiny_destructors.o core/smallobject_hotbox_v3.o core/smallobject_hotbox_v4.o core/smallobject_hotbox_v5.o core/smallsegment_v5.o core/smallobject_cold_iface_v5.o core/smallsegment_v6.o core/smallobject_cold_iface_v6.o core/smallobject_core_v6.o core/region_id_v6.o core/smallsegment_v7.o core/smallobject_cold_iface_v7.o core/mid_hotbox_v3.o core/smallobject_policy_v7.o
+OBJS_BASE = hakmem.o hakmem_config.o hakmem_tiny_config.o hakmem_ucb1.o hakmem_bigcache.o hakmem_pool.o hakmem_l25_pool.o hakmem_site_rules.o hakmem_tiny.o core/box/ss_allocation_box.o superslab_stats.o superslab_cache.o superslab_ace.o superslab_slab.o superslab_backend.o core/superslab_head_stub.o hakmem_smallmid.o tiny_sticky.o tiny_remote.o tiny_publish.o tiny_debug_ring.o hakmem_tiny_magazine.o hakmem_tiny_stats.o hakmem_tiny_sfc.o hakmem_tiny_query.o hakmem_tiny_rss.o hakmem_tiny_registry.o hakmem_tiny_remote_target.o hakmem_tiny_bg_spill.o tiny_adaptive_sizing.o hakmem_super_registry.o hakmem_shared_pool.o hakmem_shared_pool_acquire.o hakmem_shared_pool_release.o hakmem_elo.o hakmem_batch.o hakmem_p2.o hakmem_sizeclass_dist.o hakmem_evo.o hakmem_debug.o hakmem_sys.o hakmem_whale.o hakmem_policy.o hakmem_ace.o hakmem_ace_stats.o hakmem_prof.o hakmem_learner.o hakmem_size_hist.o hakmem_learn_log.o hakmem_syscall.o hakmem_ace_metrics.o hakmem_ace_ucb1.o hakmem_ace_controller.o tiny_fastcache.o core/box/superslab_expansion_box.o core/box/integrity_box.o core/box/free_publish_box.o core/box/mailbox_box.o core/box/front_gate_box.o core/box/front_gate_classifier.o core/box/capacity_box.o core/box/carve_push_box.o core/box/prewarm_box.o core/box/ss_hot_prewarm_box.o core/box/front_metrics_box.o core/box/bench_fast_box.o core/box/ss_addr_map_box.o core/box/slab_recycling_box.o core/box/pagefault_telemetry_box.o core/box/tiny_sizeclass_hist_box.o core/box/tiny_env_box.o core/box/tiny_route_box.o core/box/free_front_v3_env_box.o core/box/free_path_stats_box.o core/box/free_dispatch_stats_box.o core/box/alloc_gate_stats_box.o core/box/tiny_c6_ultra_free_box.o core/box/tiny_c5_ultra_free_box.o core/box/tiny_c4_ultra_free_box.o core/box/tiny_page_box.o core/box/tiny_class_policy_box.o core/box/tiny_class_stats_box.o core/box/tiny_policy_learner_box.o core/box/ss_budget_box.o core/box/tiny_mem_stats_box.o core/box/c7_meta_used_counter_box.o core/box/wrapper_env_box.o core/box/madvise_guard_box.o core/box/libm_reloc_guard_box.o core/box/ptr_trace_box.o core/box/link_missing_stubs.o core/box/super_reg_box.o core/box/shared_pool_box.o core/box/remote_side_box.o core/page_arena.o core/front/tiny_unified_cache.o core/tiny_alloc_fast_push.o core/tiny_c7_ultra_segment.o core/tiny_c7_ultra.o core/link_stubs.o core/tiny_failfast.o core/tiny_destructors.o core/smallobject_hotbox_v3.o core/smallobject_hotbox_v4.o core/smallobject_hotbox_v5.o core/smallsegment_v5.o core/smallobject_cold_iface_v5.o core/smallsegment_v6.o core/smallobject_cold_iface_v6.o core/smallobject_core_v6.o core/region_id_v6.o core/smallsegment_v7.o core/smallobject_cold_iface_v7.o core/mid_hotbox_v3.o core/smallobject_policy_v7.o core/smallobject_segment_mid_v3.o core/smallobject_cold_iface_mid_v3.o core/smallobject_stats_mid_v3.o core/smallobject_learner_v2.o
 OBJS = $(OBJS_BASE)
 
 # Shared library
@@ -250,7 +250,7 @@ endif
 # Benchmark targets
 BENCH_HAKMEM = bench_allocators_hakmem
 BENCH_SYSTEM = bench_allocators_system
-BENCH_HAKMEM_OBJS_BASE = hakmem.o hakmem_config.o hakmem_tiny_config.o hakmem_ucb1.o hakmem_bigcache.o hakmem_pool.o hakmem_l25_pool.o hakmem_site_rules.o hakmem_tiny.o core/box/ss_allocation_box.o superslab_stats.o superslab_cache.o superslab_ace.o superslab_slab.o superslab_backend.o core/superslab_head_stub.o hakmem_smallmid.o tiny_sticky.o tiny_remote.o tiny_publish.o tiny_debug_ring.o hakmem_tiny_magazine.o hakmem_tiny_stats.o hakmem_tiny_sfc.o hakmem_tiny_query.o hakmem_tiny_rss.o hakmem_tiny_registry.o hakmem_tiny_remote_target.o hakmem_tiny_bg_spill.o tiny_adaptive_sizing.o hakmem_super_registry.o hakmem_shared_pool.o hakmem_shared_pool_acquire.o hakmem_shared_pool_release.o hakmem_elo.o hakmem_batch.o hakmem_p2.o hakmem_sizeclass_dist.o hakmem_evo.o hakmem_debug.o hakmem_sys.o hakmem_whale.o hakmem_policy.o hakmem_ace.o hakmem_ace_stats.o hakmem_prof.o hakmem_learner.o hakmem_size_hist.o hakmem_learn_log.o hakmem_syscall.o hakmem_ace_metrics.o hakmem_ace_ucb1.o hakmem_ace_controller.o tiny_fastcache.o core/box/superslab_expansion_box.o core/box/integrity_box.o core/box/free_publish_box.o core/box/mailbox_box.o core/box/front_gate_box.o core/box/front_gate_classifier.o core/box/capacity_box.o core/box/carve_push_box.o core/box/prewarm_box.o core/box/ss_hot_prewarm_box.o core/box/front_metrics_box.o core/box/bench_fast_box.o core/box/ss_addr_map_box.o core/box/slab_recycling_box.o core/box/pagefault_telemetry_box.o core/box/tiny_sizeclass_hist_box.o core/box/tiny_env_box.o core/box/tiny_route_box.o core/box/free_front_v3_env_box.o core/box/free_path_stats_box.o core/box/free_dispatch_stats_box.o core/box/alloc_gate_stats_box.o core/box/tiny_c6_ultra_free_box.o core/box/tiny_c5_ultra_free_box.o core/box/tiny_c4_ultra_free_box.o core/box/tiny_page_box.o core/box/tiny_class_policy_box.o core/box/tiny_class_stats_box.o core/box/tiny_policy_learner_box.o core/box/ss_budget_box.o core/box/tiny_mem_stats_box.o core/box/c7_meta_used_counter_box.o core/box/wrapper_env_box.o core/box/madvise_guard_box.o core/box/libm_reloc_guard_box.o core/box/ptr_trace_box.o core/box/link_missing_stubs.o core/box/super_reg_box.o core/box/shared_pool_box.o core/box/remote_side_box.o core/page_arena.o core/front/tiny_unified_cache.o core/tiny_alloc_fast_push.o core/tiny_c7_ultra_segment.o core/tiny_c7_ultra.o core/link_stubs.o core/tiny_failfast.o core/tiny_destructors.o core/smallobject_hotbox_v3.o core/smallobject_hotbox_v4.o core/smallobject_hotbox_v5.o core/smallsegment_v5.o core/smallobject_cold_iface_v5.o core/smallsegment_v6.o core/smallobject_cold_iface_v6.o core/smallobject_core_v6.o core/region_id_v6.o core/smallsegment_v7.o core/smallobject_cold_iface_v7.o core/mid_hotbox_v3.o core/smallobject_policy_v7.o bench_allocators_hakmem.o
+BENCH_HAKMEM_OBJS_BASE = hakmem.o hakmem_config.o hakmem_tiny_config.o hakmem_ucb1.o hakmem_bigcache.o hakmem_pool.o hakmem_l25_pool.o hakmem_site_rules.o hakmem_tiny.o core/box/ss_allocation_box.o superslab_stats.o superslab_cache.o superslab_ace.o superslab_slab.o superslab_backend.o core/superslab_head_stub.o hakmem_smallmid.o tiny_sticky.o tiny_remote.o tiny_publish.o tiny_debug_ring.o hakmem_tiny_magazine.o hakmem_tiny_stats.o hakmem_tiny_sfc.o hakmem_tiny_query.o hakmem_tiny_rss.o hakmem_tiny_registry.o hakmem_tiny_remote_target.o hakmem_tiny_bg_spill.o tiny_adaptive_sizing.o hakmem_super_registry.o hakmem_shared_pool.o hakmem_shared_pool_acquire.o hakmem_shared_pool_release.o hakmem_elo.o hakmem_batch.o hakmem_p2.o hakmem_sizeclass_dist.o hakmem_evo.o hakmem_debug.o hakmem_sys.o hakmem_whale.o hakmem_policy.o hakmem_ace.o hakmem_ace_stats.o hakmem_prof.o hakmem_learner.o hakmem_size_hist.o hakmem_learn_log.o hakmem_syscall.o hakmem_ace_metrics.o hakmem_ace_ucb1.o hakmem_ace_controller.o tiny_fastcache.o core/box/superslab_expansion_box.o core/box/integrity_box.o core/box/free_publish_box.o core/box/mailbox_box.o core/box/front_gate_box.o core/box/front_gate_classifier.o core/box/capacity_box.o core/box/carve_push_box.o core/box/prewarm_box.o core/box/ss_hot_prewarm_box.o core/box/front_metrics_box.o core/box/bench_fast_box.o core/box/ss_addr_map_box.o core/box/slab_recycling_box.o core/box/pagefault_telemetry_box.o core/box/tiny_sizeclass_hist_box.o core/box/tiny_env_box.o core/box/tiny_route_box.o core/box/free_front_v3_env_box.o core/box/free_path_stats_box.o core/box/free_dispatch_stats_box.o core/box/alloc_gate_stats_box.o core/box/tiny_c6_ultra_free_box.o core/box/tiny_c5_ultra_free_box.o core/box/tiny_c4_ultra_free_box.o core/box/tiny_page_box.o core/box/tiny_class_policy_box.o core/box/tiny_class_stats_box.o core/box/tiny_policy_learner_box.o core/box/ss_budget_box.o core/box/tiny_mem_stats_box.o core/box/c7_meta_used_counter_box.o core/box/wrapper_env_box.o core/box/madvise_guard_box.o core/box/libm_reloc_guard_box.o core/box/ptr_trace_box.o core/box/link_missing_stubs.o core/box/super_reg_box.o core/box/shared_pool_box.o core/box/remote_side_box.o core/page_arena.o core/front/tiny_unified_cache.o core/tiny_alloc_fast_push.o core/tiny_c7_ultra_segment.o core/tiny_c7_ultra.o core/link_stubs.o core/tiny_failfast.o core/tiny_destructors.o core/smallobject_hotbox_v3.o core/smallobject_hotbox_v4.o core/smallobject_hotbox_v5.o core/smallsegment_v5.o core/smallobject_cold_iface_v5.o core/smallsegment_v6.o core/smallobject_cold_iface_v6.o core/smallobject_core_v6.o core/region_id_v6.o core/smallsegment_v7.o core/smallobject_cold_iface_v7.o core/mid_hotbox_v3.o core/smallobject_policy_v7.o core/smallobject_segment_mid_v3.o core/smallobject_cold_iface_mid_v3.o core/smallobject_stats_mid_v3.o core/smallobject_learner_v2.o bench_allocators_hakmem.o
 BENCH_HAKMEM_OBJS = $(BENCH_HAKMEM_OBJS_BASE)
 ifeq ($(POOL_TLS_PHASE1),1)
 BENCH_HAKMEM_OBJS += pool_tls.o pool_refill.o pool_tls_arena.o pool_tls_registry.o pool_tls_remote.o
@@ -427,7 +427,7 @@ test-box-refactor: box-refactor
 	./larson_hakmem 10 8 128 1024 1 12345 4
 
 # Phase 4: Tiny Pool benchmarks (properly linked with hakmem)
-TINY_BENCH_OBJS_BASE = hakmem.o hakmem_config.o hakmem_tiny_config.o hakmem_ucb1.o hakmem_bigcache.o hakmem_pool.o hakmem_l25_pool.o hakmem_site_rules.o hakmem_tiny.o core/box/ss_allocation_box.o superslab_stats.o superslab_cache.o superslab_ace.o superslab_slab.o superslab_backend.o core/superslab_head_stub.o hakmem_smallmid.o core/box/superslab_expansion_box.o core/box/integrity_box.o core/box/mailbox_box.o core/box/front_gate_box.o core/box/front_gate_classifier.o core/box/free_publish_box.o core/box/capacity_box.o core/box/carve_push_box.o core/box/prewarm_box.o core/box/ss_hot_prewarm_box.o core/box/front_metrics_box.o core/box/bench_fast_box.o core/box/ss_addr_map_box.o core/box/slab_recycling_box.o core/box/pagefault_telemetry_box.o core/box/tiny_sizeclass_hist_box.o core/box/tiny_env_box.o core/box/tiny_route_box.o core/box/free_front_v3_env_box.o core/box/free_path_stats_box.o core/box/free_dispatch_stats_box.o core/box/alloc_gate_stats_box.o core/box/tiny_c6_ultra_free_box.o core/box/tiny_c5_ultra_free_box.o core/box/tiny_c4_ultra_free_box.o core/box/tiny_page_box.o core/box/tiny_class_policy_box.o core/box/tiny_class_stats_box.o core/box/tiny_policy_learner_box.o core/box/ss_budget_box.o core/box/tiny_mem_stats_box.o core/box/c7_meta_used_counter_box.o core/box/wrapper_env_box.o core/box/madvise_guard_box.o core/box/libm_reloc_guard_box.o core/box/ptr_trace_box.o core/box/link_missing_stubs.o core/box/super_reg_box.o core/box/shared_pool_box.o core/box/remote_side_box.o core/page_arena.o core/front/tiny_unified_cache.o tiny_sticky.o tiny_remote.o tiny_publish.o tiny_debug_ring.o hakmem_tiny_magazine.o hakmem_tiny_stats.o hakmem_tiny_sfc.o hakmem_tiny_query.o hakmem_tiny_rss.o hakmem_tiny_registry.o hakmem_tiny_remote_target.o hakmem_tiny_bg_spill.o tiny_adaptive_sizing.o hakmem_super_registry.o hakmem_shared_pool.o hakmem_shared_pool_acquire.o hakmem_shared_pool_release.o hakmem_elo.o hakmem_batch.o hakmem_p2.o hakmem_sizeclass_dist.o hakmem_evo.o hakmem_debug.o hakmem_sys.o hakmem_whale.o hakmem_policy.o hakmem_ace.o hakmem_ace_stats.o hakmem_prof.o hakmem_learner.o hakmem_size_hist.o hakmem_learn_log.o hakmem_syscall.o hakmem_ace_metrics.o hakmem_ace_ucb1.o hakmem_ace_controller.o tiny_fastcache.o core/tiny_alloc_fast_push.o core/tiny_c7_ultra_segment.o core/tiny_c7_ultra.o core/link_stubs.o core/tiny_failfast.o core/tiny_destructors.o core/smallobject_hotbox_v3.o core/smallobject_hotbox_v4.o core/smallobject_hotbox_v5.o core/smallsegment_v5.o core/smallobject_cold_iface_v5.o core/smallsegment_v6.o core/smallobject_cold_iface_v6.o core/smallobject_core_v6.o core/region_id_v6.o core/smallsegment_v7.o core/smallobject_cold_iface_v7.o core/mid_hotbox_v3.o core/smallobject_policy_v7.o
+TINY_BENCH_OBJS_BASE = hakmem.o hakmem_config.o hakmem_tiny_config.o hakmem_ucb1.o hakmem_bigcache.o hakmem_pool.o hakmem_l25_pool.o hakmem_site_rules.o hakmem_tiny.o core/box/ss_allocation_box.o superslab_stats.o superslab_cache.o superslab_ace.o superslab_slab.o superslab_backend.o core/superslab_head_stub.o hakmem_smallmid.o core/box/superslab_expansion_box.o core/box/integrity_box.o core/box/mailbox_box.o core/box/front_gate_box.o core/box/front_gate_classifier.o core/box/free_publish_box.o core/box/capacity_box.o core/box/carve_push_box.o core/box/prewarm_box.o core/box/ss_hot_prewarm_box.o core/box/front_metrics_box.o core/box/bench_fast_box.o core/box/ss_addr_map_box.o core/box/slab_recycling_box.o core/box/pagefault_telemetry_box.o core/box/tiny_sizeclass_hist_box.o core/box/tiny_env_box.o core/box/tiny_route_box.o core/box/free_front_v3_env_box.o core/box/free_path_stats_box.o core/box/free_dispatch_stats_box.o core/box/alloc_gate_stats_box.o core/box/tiny_c6_ultra_free_box.o core/box/tiny_c5_ultra_free_box.o core/box/tiny_c4_ultra_free_box.o core/box/tiny_page_box.o core/box/tiny_class_policy_box.o core/box/tiny_class_stats_box.o core/box/tiny_policy_learner_box.o core/box/ss_budget_box.o core/box/tiny_mem_stats_box.o core/box/c7_meta_used_counter_box.o core/box/wrapper_env_box.o core/box/madvise_guard_box.o core/box/libm_reloc_guard_box.o core/box/ptr_trace_box.o core/box/link_missing_stubs.o core/box/super_reg_box.o core/box/shared_pool_box.o core/box/remote_side_box.o core/page_arena.o core/front/tiny_unified_cache.o tiny_sticky.o tiny_remote.o tiny_publish.o tiny_debug_ring.o hakmem_tiny_magazine.o hakmem_tiny_stats.o hakmem_tiny_sfc.o hakmem_tiny_query.o hakmem_tiny_rss.o hakmem_tiny_registry.o hakmem_tiny_remote_target.o hakmem_tiny_bg_spill.o tiny_adaptive_sizing.o hakmem_super_registry.o hakmem_shared_pool.o hakmem_shared_pool_acquire.o hakmem_shared_pool_release.o hakmem_elo.o hakmem_batch.o hakmem_p2.o hakmem_sizeclass_dist.o hakmem_evo.o hakmem_debug.o hakmem_sys.o hakmem_whale.o hakmem_policy.o hakmem_ace.o hakmem_ace_stats.o hakmem_prof.o hakmem_learner.o hakmem_size_hist.o hakmem_learn_log.o hakmem_syscall.o hakmem_ace_metrics.o hakmem_ace_ucb1.o hakmem_ace_controller.o tiny_fastcache.o core/tiny_alloc_fast_push.o core/tiny_c7_ultra_segment.o core/tiny_c7_ultra.o core/link_stubs.o core/tiny_failfast.o core/tiny_destructors.o core/smallobject_hotbox_v3.o core/smallobject_hotbox_v4.o core/smallobject_hotbox_v5.o core/smallsegment_v5.o core/smallobject_cold_iface_v5.o core/smallsegment_v6.o core/smallobject_cold_iface_v6.o core/smallobject_core_v6.o core/region_id_v6.o core/smallsegment_v7.o core/smallobject_cold_iface_v7.o core/mid_hotbox_v3.o core/smallobject_policy_v7.o core/smallobject_segment_mid_v3.o core/smallobject_cold_iface_mid_v3.o core/smallobject_stats_mid_v3.o core/smallobject_learner_v2.o
 TINY_BENCH_OBJS = $(TINY_BENCH_OBJS_BASE)
 ifeq ($(POOL_TLS_PHASE1),1)
 TINY_BENCH_OBJS += pool_tls.o pool_refill.o core/pool_tls_arena.o pool_tls_registry.o pool_tls_remote.o
diff --git a/core/box/smallobject_cold_iface_mid_v3_box.h b/core/box/smallobject_cold_iface_mid_v3_box.h
new file mode 100644
index 00000000..ddf0a38e
--- /dev/null
+++ b/core/box/smallobject_cold_iface_mid_v3_box.h
@@ -0,0 +1,39 @@
+// smallobject_cold_iface_mid_v3_box.h
+// Phase v11a-2: Cold interface for MID v3.5 (L2→L1 boundary)
+
+#ifndef SMALLOBJECT_COLD_IFACE_MID_V3_BOX_H
+#define SMALLOBJECT_COLD_IFACE_MID_V3_BOX_H
+
+#include <stdint.h>
+#include "smallobject_segment_mid_v3_box.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+// Forward declaration
+struct SmallPageMeta;
+
+// ============================================================================
+// Cold Interface API (L2→L1)
+// ============================================================================
+
+/**
+ * Refill: Get a new page for allocation
+ * Called from hot path when TLS page is exhausted
+ * Returns SmallPageMeta* or NULL if no pages available
+ */
+struct SmallPageMeta* small_cold_mid_v3_refill_page(uint32_t class_idx);
+
+/**
+ * Retire: Return a page to the free pool
+ * Called when a page is full or evicted from TLS cache
+ * Publishes stats to Learner before returning to free stack
+ */
+void small_cold_mid_v3_retire_page(struct SmallPageMeta *page);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif // SMALLOBJECT_COLD_IFACE_MID_V3_BOX_H
diff --git a/core/box/smallobject_learner_v2_box.h b/core/box/smallobject_learner_v2_box.h
index 11604722..7bb905ba 100644
--- a/core/box/smallobject_learner_v2_box.h
+++ b/core/box/smallobject_learner_v2_box.h
@@ -6,6 +6,7 @@
 
 #include <stdint.h>
 #include <stdbool.h>
+#include "smallobject_stats_mid_v3_box.h"  // For SmallPageStatsMID_v3, SmallPageStatsAggregate_MID_v3
 
 #ifdef __cplusplus
 extern "C" {
@@ -77,6 +78,12 @@ void small_learner_v2_record_refill(uint32_t class_idx, uint64_t capacity);
 void small_learner_v2_record_retire(uint32_t class_idx,
                                     uint32_t free_hit_ratio_bps);
 
+/**
+ * Record page stats (from StatsBox publish)
+ * Called when page is retired with full stats
+ */
+void small_learner_v2_record_page_stats(const SmallPageStatsMID_v3 *stat);
+
 /**
  * Ingest aggregated stats from stats collector
  * Called periodically by stats module
diff --git a/core/box/smallobject_segment_mid_v3_box.h b/core/box/smallobject_segment_mid_v3_box.h
index 09832930..7df38535 100644
--- a/core/box/smallobject_segment_mid_v3_box.h
+++ b/core/box/smallobject_segment_mid_v3_box.h
@@ -121,6 +121,24 @@ bool small_segment_mid_v3_refill_page(
 // Page Lifecycle
 // ============================================================================
 
+/**
+ * Take a page from the free stack (LIFO)
+ * Returns page pointer or NULL if no pages available
+ */
+void* small_segment_mid_v3_take_page(
+    SmallSegment_MID_v3 *seg,
+    uint32_t class_idx
+);
+
+/**
+ * Release a page back to the free stack (LIFO)
+ */
+void small_segment_mid_v3_release_page(
+    SmallSegment_MID_v3 *seg,
+    void *page,
+    uint32_t class_idx
+);
+
 /**
  * Retire a full page back to free stack
  * Records stats for Learner
diff --git a/core/smallobject_cold_iface_mid_v3.c b/core/smallobject_cold_iface_mid_v3.c
new file mode 100644
index 00000000..22061262
--- /dev/null
+++ b/core/smallobject_cold_iface_mid_v3.c
@@ -0,0 +1,114 @@
+// smallobject_cold_iface_mid_v3.c
+// Phase v11a-2: Cold interface implementation for MID v3.5
+
+#include <stdlib.h>
+#include <stdio.h>
+#include "box/smallobject_cold_iface_mid_v3_box.h"
+#include "box/smallobject_stats_mid_v3_box.h"
+
+// Reuse SmallPageMeta from segment implementation
+typedef struct SmallPageMeta {
+    void *ptr;
+    uint32_t capacity;
+    uint8_t class_idx;
+    uint32_t alloc_count;
+    uint32_t free_count;
+    void *segment;
+    struct SmallPageMeta *next;
+} SmallPageMeta;
+
+// ============================================================================
+// TLS Segment Management
+// ============================================================================
+
+// Thread-local segment (simplified for v11a-2)
+static __thread SmallSegment_MID_v3 *tls_mid_segment = NULL;
+
+// ============================================================================
+// Helper: class_idx to slots
+// ============================================================================
+
+static uint32_t class_idx_to_slots(uint32_t class_idx) {
+    switch (class_idx) {
+        case 5: return 170;  // C5: 257-384B
+        case 6: return 102;  // C6: 385-640B
+        case 7: return 64;   // C7: 641-1024B
+        default: return 0;
+    }
+}
+
+// ============================================================================
+// Cold Interface Implementation
+// ============================================================================
+
+struct SmallPageMeta* small_cold_mid_v3_refill_page(uint32_t class_idx) {
+    // Ensure TLS segment exists
+    if (!tls_mid_segment) {
+        tls_mid_segment = small_segment_mid_v3_create();
+        if (!tls_mid_segment) {
+            return NULL;
+        }
+    }
+
+    // Try to take a page from the free stack
+    void *page_ptr = small_segment_mid_v3_take_page(tls_mid_segment, class_idx);
+    if (!page_ptr) {
+        // No free pages available
+        // In full implementation, would allocate new segment here
+        // For v11a-2: just return NULL
+        return NULL;
+    }
+
+    // Get page metadata
+    SmallPageMeta *page = (SmallPageMeta*)small_segment_mid_v3_get_page_meta(
+        tls_mid_segment, page_ptr
+    );
+
+    if (!page) {
+        // Failed to get metadata
+        return NULL;
+    }
+
+    // Initialize page for allocation
+    page->class_idx = class_idx;
+    page->capacity = class_idx_to_slots(class_idx);
+    page->alloc_count = 0;
+    page->free_count = 0;
+
+    return page;
+}
+
+void small_cold_mid_v3_retire_page(struct SmallPageMeta *page) {
+    if (!page || !page->segment) {
+        return;
+    }
+
+    SmallSegment_MID_v3 *seg = (SmallSegment_MID_v3*)page->segment;
+
+    // Calculate free hit ratio (in basis points, 0-10000)
+    uint32_t free_hit_ratio_bps = 0;
+    if (page->alloc_count > 0) {
+        free_hit_ratio_bps = (page->free_count * 10000) / page->alloc_count;
+    }
+
+    // Publish stats to StatsBox
+    SmallPageStatsMID_v3 stat = {
+        .class_idx = page->class_idx,
+        .total_allocations = page->alloc_count,
+        .total_frees = page->free_count,
+        .page_alloc_count = page->capacity,
+        .free_hit_ratio_bps = free_hit_ratio_bps,
+        .lifetime_ns = 0  // Not tracking lifetime in v11a-2
+    };
+
+    small_stats_mid_v3_publish(&stat);
+
+    // Reset page metadata
+    uint8_t old_class_idx = page->class_idx;
+    page->class_idx = 0xFF;  // Mark as unassigned
+    page->alloc_count = 0;
+    page->free_count = 0;
+
+    // Return page to free stack
+    small_segment_mid_v3_release_page(seg, page->ptr, old_class_idx);
+}
diff --git a/core/smallobject_learner_v2.c b/core/smallobject_learner_v2.c
new file mode 100644
index 00000000..4d390d27
--- /dev/null
+++ b/core/smallobject_learner_v2.c
@@ -0,0 +1,319 @@
+// smallobject_learner_v2.c
+// Phase v11a-2: Extended Learner for multi-dimensional MID v3.5 optimization
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <time.h>
+#include "box/smallobject_learner_v2_box.h"
+#include "box/smallobject_stats_mid_v3_box.h"
+
+// ============================================================================
+// Helper: Get timestamp
+// ============================================================================
+
+static inline uint64_t get_timestamp_ns(void) {
+    struct timespec ts;
+    clock_gettime(CLOCK_MONOTONIC, &ts);
+    return (uint64_t)ts.tv_sec * 1000000000ULL + (uint64_t)ts.tv_nsec;
+}
+
+static inline uint32_t get_timestamp_ms(void) {
+    return (uint32_t)(get_timestamp_ns() / 1000000ULL);
+}
+
+// ============================================================================
+// Global Learner State
+// ============================================================================
+
+static SmallLearnerStatsV2 g_learner_v2_stats = {0};
+static SmallLearnerClassStatsV2 g_learner_class_stats[8] = {0};
+
+// Configuration
+static uint32_t g_c5_threshold_pct = SMALL_LEARNER_C5_THRESHOLD_PCT;
+static uint32_t g_eval_interval = SMALL_LEARNER_EVAL_INTERVAL;
+static uint32_t g_smoothing_factor = SMALL_LEARNER_SMOOTHING_FACTOR_PCT;
+static bool g_logging_enabled = false;
+
+// ============================================================================
+// Event Recording
+// ============================================================================
+
+void small_learner_v2_record_refill(uint32_t class_idx, uint64_t capacity) {
+    if (class_idx >= 8) return;
+
+    SmallLearnerStatsV2 *learn = &g_learner_v2_stats;
+    SmallLearnerClassStatsV2 *cls = &g_learner_class_stats[class_idx];
+
+    learn->allocs[class_idx] += capacity;
+    learn->total_allocations += capacity;
+
+    cls->allocs += capacity;
+    cls->sample_count++;
+    cls->last_update_ns = get_timestamp_ns();
+}
+
+void small_learner_v2_record_retire(uint32_t class_idx, uint32_t free_hit_ratio_bps) {
+    if (class_idx >= 8) return;
+
+    SmallLearnerStatsV2 *learn = &g_learner_v2_stats;
+    SmallLearnerClassStatsV2 *cls = &g_learner_class_stats[class_idx];
+
+    learn->retire_count[class_idx]++;
+    learn->total_retires++;
+
+    // Exponential smoothing for retire ratio
+    uint32_t alpha = g_smoothing_factor;  // 0-100
+    uint32_t new_val = free_hit_ratio_bps / 100;  // Convert to percentage
+
+    if (cls->retire_ratio_smoothed == 0) {
+        // First sample
+        cls->retire_ratio_smoothed = new_val;
+    } else {
+        // EMA: smoothed = (1-alpha) * smoothed + alpha * new_val
+        uint32_t smoothed = ((100 - alpha) * cls->retire_ratio_smoothed + alpha * new_val) / 100;
+        cls->retire_ratio_smoothed = smoothed;
+    }
+
+    learn->retire_ratio_pct[class_idx] = cls->retire_ratio_smoothed;
+
+    cls->sample_count++;
+    cls->last_update_ns = get_timestamp_ns();
+}
+
+void small_learner_v2_record_page_stats(const SmallPageStatsMID_v3 *stat) {
+    if (!stat || stat->class_idx >= 8) return;
+
+    SmallLearnerStatsV2 *learn = &g_learner_v2_stats;
+    SmallLearnerClassStatsV2 *cls = &g_learner_class_stats[stat->class_idx];
+
+    // Record allocations
+    learn->allocs[stat->class_idx] += stat->total_allocations;
+    learn->total_allocations += stat->total_allocations;
+
+    // Record retires
+    learn->retire_count[stat->class_idx]++;
+    learn->total_retires++;
+
+    // Exponential smoothing for free hit ratio
+    uint32_t alpha = g_smoothing_factor;
+    uint32_t new_val = stat->free_hit_ratio_bps / 100;  // Convert to percentage
+
+    if (cls->retire_ratio_smoothed == 0) {
+        cls->retire_ratio_smoothed = new_val;
+    } else {
+        uint32_t smoothed = ((100 - alpha) * cls->retire_ratio_smoothed + alpha * new_val) / 100;
+        cls->retire_ratio_smoothed = smoothed;
+    }
+
+    learn->retire_ratio_pct[stat->class_idx] = cls->retire_ratio_smoothed;
+
+    // Update global free hit ratio (EMA)
+    if (learn->free_hit_ratio_bps == 0) {
+        learn->free_hit_ratio_bps = stat->free_hit_ratio_bps;
+    } else {
+        uint32_t smoothed = ((100 - alpha) * learn->free_hit_ratio_bps + alpha * stat->free_hit_ratio_bps) / 100;
+        learn->free_hit_ratio_bps = smoothed;
+    }
+
+    // Update class stats
+    cls->allocs += stat->total_allocations;
+    cls->sample_count++;
+    cls->last_update_ns = get_timestamp_ns();
+
+    // Log if enabled
+    if (g_logging_enabled) {
+        fprintf(stderr, "[Learner_v2] C%u: allocs=%lu retire_ratio=%u%% free_hit=%u bps\n",
+                stat->class_idx, stat->total_allocations,
+                cls->retire_ratio_smoothed, stat->free_hit_ratio_bps);
+    }
+}
+
+void small_learner_v2_ingest_stats(const SmallPageStatsAggregate_MID_v3 *agg) {
+    if (!agg) return;
+
+    SmallLearnerStatsV2 *learn = &g_learner_v2_stats;
+
+    // Update from aggregated stats
+    for (int i = 0; i < 8; i++) {
+        learn->allocs[i] = agg->class_allocations[i];
+        learn->retire_count[i] = agg->class_retire_count[i];
+
+        // Update retire ratio from aggregate
+        if (agg->class_retire_count[i] > 0) {
+            uint32_t avg_ratio_pct = agg->class_avg_free_hit_bps[i] / 100;
+            learn->retire_ratio_pct[i] = avg_ratio_pct;
+            g_learner_class_stats[i].retire_ratio_smoothed = avg_ratio_pct;
+        }
+    }
+
+    learn->total_allocations = agg->total_allocations;
+    learn->total_retires = agg->total_pages_retired;
+    learn->free_hit_ratio_bps = agg->global_avg_free_hit_bps;
+    learn->sample_count = agg->eval_count;
+}
+
+// ============================================================================
+// Evaluation & Decision Making
+// ============================================================================
+
+void small_learner_v2_evaluate(void) {
+    SmallLearnerStatsV2 *learn = &g_learner_v2_stats;
+
+    learn->eval_count++;
+    learn->last_eval_timestamp_ms = get_timestamp_ms();
+
+    // Calculate average page utilization
+    if (learn->total_retires > 0) {
+        uint64_t total_capacity = 0;
+        uint64_t total_used = 0;
+
+        for (int i = 0; i < 8; i++) {
+            if (learn->retire_count[i] > 0) {
+                // Estimate capacity based on retire ratio
+                total_capacity += learn->allocs[i];
+                total_used += (learn->allocs[i] * learn->retire_ratio_pct[i]) / 100;
+            }
+        }
+
+        if (total_capacity > 0) {
+            learn->avg_page_utilization = (total_used * 10000) / total_capacity;
+        }
+    }
+
+    if (g_logging_enabled) {
+        fprintf(stderr, "[Learner_v2] Eval #%lu: total_allocs=%lu retires=%lu util=%lu bps\n",
+                learn->eval_count, learn->total_allocations,
+                learn->total_retires, learn->avg_page_utilization);
+    }
+}
+
+const SmallLearnerStatsV2* small_learner_v2_stats_snapshot(void) {
+    return &g_learner_v2_stats;
+}
+
+const SmallLearnerClassStatsV2* small_learner_v2_class_stats(uint32_t class_idx) {
+    if (class_idx >= 8) return NULL;
+    return &g_learner_class_stats[class_idx];
+}
+
+// ============================================================================
+// Routing Decision Support
+// ============================================================================
+
+int small_learner_v2_should_use_v7(uint32_t class_idx) {
+    (void)class_idx;  // Unused in v11a-2
+
+    // Decision based on C5 ratio
+    uint32_t c5_ratio = small_learner_v2_c5_ratio_pct();
+
+    if (c5_ratio >= g_c5_threshold_pct) {
+        return 1;  // Use v7
+    }
+
+    return 0;  // Use MID_v3
+}
+
+uint32_t small_learner_v2_c5_ratio_pct(void) {
+    SmallLearnerStatsV2 *learn = &g_learner_v2_stats;
+
+    if (learn->total_allocations == 0) {
+        return 0;
+    }
+
+    return (uint32_t)((learn->allocs[5] * 100) / learn->total_allocations);
+}
+
+uint32_t small_learner_v2_class_ratio_pct(uint32_t class_idx) {
+    if (class_idx >= 8) return 0;
+
+    SmallLearnerStatsV2 *learn = &g_learner_v2_stats;
+
+    if (learn->total_allocations == 0) {
+        return 0;
+    }
+
+    return (uint32_t)((learn->allocs[class_idx] * 100) / learn->total_allocations);
+}
+
+uint32_t small_learner_v2_retire_efficiency_pct(uint32_t class_idx) {
+    if (class_idx >= 8) return 0;
+    return g_learner_v2_stats.retire_ratio_pct[class_idx];
+}
+
+// ============================================================================
+// Configuration & Control
+// ============================================================================
+
+bool small_learner_v2_enabled(void) {
+    const char *env = getenv("HAKMEM_SMALL_LEARNER_V7_ENABLED");
+    return (env && *env && *env != '0');
+}
+
+void small_learner_v2_set_c5_threshold_pct(uint32_t threshold) {
+    g_c5_threshold_pct = threshold;
+}
+
+uint32_t small_learner_v2_get_c5_threshold_pct(void) {
+    return g_c5_threshold_pct;
+}
+
+void small_learner_v2_set_eval_interval(uint32_t interval) {
+    g_eval_interval = interval > 0 ? interval : SMALL_LEARNER_EVAL_INTERVAL;
+}
+
+void small_learner_v2_set_smoothing_factor(uint32_t factor_pct) {
+    if (factor_pct > 100) factor_pct = 100;
+    g_smoothing_factor = factor_pct;
+}
+
+void small_learner_v2_set_logging_enabled(bool enabled) {
+    g_logging_enabled = enabled;
+}
+
+void small_learner_v2_reset(void) {
+    memset(&g_learner_v2_stats, 0, sizeof(g_learner_v2_stats));
+    memset(&g_learner_class_stats, 0, sizeof(g_learner_class_stats));
+    g_c5_threshold_pct = SMALL_LEARNER_C5_THRESHOLD_PCT;
+    g_eval_interval = SMALL_LEARNER_EVAL_INTERVAL;
+    g_smoothing_factor = SMALL_LEARNER_SMOOTHING_FACTOR_PCT;
+}
+
+// ============================================================================
+// Debugging & Monitoring
+// ============================================================================
+
+void small_learner_v2_print_stats(void) {
+    const SmallLearnerStatsV2 *learn = &g_learner_v2_stats;
+
+    fprintf(stderr, "[Learner_v2] Statistics:\n");
+    fprintf(stderr, "  total_allocations=%lu total_retires=%lu\n",
+            learn->total_allocations, learn->total_retires);
+    fprintf(stderr, "  avg_page_util=%lu bps (%.2f%%) free_hit=%u bps\n",
+            learn->avg_page_utilization, learn->avg_page_utilization / 100.0,
+            learn->free_hit_ratio_bps);
+    fprintf(stderr, "  eval_count=%lu sample_count=%lu\n",
+            learn->eval_count, learn->sample_count);
+
+    for (int i = 0; i < 8; i++) {
+        if (learn->allocs[i] > 0) {
+            fprintf(stderr, "  C%d: allocs=%lu retires=%u ratio=%u%%\n",
+                    i, learn->allocs[i], learn->retire_count[i],
+                    learn->retire_ratio_pct[i]);
+        }
+    }
+}
+
+void small_learner_v2_print_decisions(void) {
+    fprintf(stderr, "[Learner_v2] Routing Decisions:\n");
+    fprintf(stderr, "  C5 threshold=%u%% current_ratio=%u%%\n",
+            g_c5_threshold_pct, small_learner_v2_c5_ratio_pct());
+
+    for (uint32_t i = 5; i <= 7; i++) {
+        int use_v7 = small_learner_v2_should_use_v7(i);
+        fprintf(stderr, "  C%u: %s (ratio=%u%% efficiency=%u%%)\n",
+                i, use_v7 ? "v7" : "MID_v3",
+                small_learner_v2_class_ratio_pct(i),
+                small_learner_v2_retire_efficiency_pct(i));
+    }
+}
diff --git a/core/smallobject_segment_mid_v3.c b/core/smallobject_segment_mid_v3.c
new file mode 100644
index 00000000..4135042b
--- /dev/null
+++ b/core/smallobject_segment_mid_v3.c
@@ -0,0 +1,294 @@
+// smallobject_segment_mid_v3.c
+// Phase v11a-2: Multi-class MID v3.5 segment implementation (L2 physical layer)
+
+#include <stdlib.h>
+#include <string.h>
+#include <sys/mman.h>
+#include <stdio.h>
+#include "box/smallobject_segment_mid_v3_box.h"
+#include "box/region_id_v6_box.h"
+
+// ============================================================================
+// SmallPageMeta - Page metadata for MID v3
+// ============================================================================
+
+typedef struct SmallPageMeta {
+    void *ptr;                      // Page base pointer
+    uint32_t capacity;              // Slots per page
+    uint8_t class_idx;              // Size class (C5-C7)
+    uint32_t alloc_count;           // Total allocations on this page
+    uint32_t free_count;            // Total frees on this page
+    void *segment;                  // Back-pointer to SmallSegment_MID_v3
+    struct SmallPageMeta *next;     // For free stack linking
+} SmallPageMeta;
+
+// ============================================================================
+// Geometry Constants
+// ============================================================================
+
+#define SMALL_MID_SEGMENT_SIZE (2 * 1024 * 1024)  // 2 MiB
+#define SMALL_MID_PAGE_SIZE (64 * 1024)            // 64 KiB
+#define SMALL_MID_PAGES_PER_SEG (SMALL_MID_SEGMENT_SIZE / SMALL_MID_PAGE_SIZE)  // 32
+
+// ============================================================================
+// Helper: class_idx to slots mapping
+// ============================================================================
+
+static uint32_t class_idx_to_slots(uint32_t class_idx) {
+    // MID v3.5 targets C5-C7 (257-1024B)
+    // C5: 257-384B  → 64KiB / 384B  ≈ 170 slots
+    // C6: 385-640B  → 64KiB / 640B  ≈ 102 slots
+    // C7: 641-1024B → 64KiB / 1024B ≈ 64 slots
+
+    switch (class_idx) {
+        case 5: return 170;  // C5
+        case 6: return 102;  // C6
+        case 7: return 64;   // C7
+        default: return 0;
+    }
+}
+
+// ============================================================================
+// Segment Lifecycle
+// ============================================================================
+
+SmallSegment_MID_v3* small_segment_mid_v3_create(void) {
+    // 1. Allocate SmallSegment_MID_v3 structure
+    SmallSegment_MID_v3 *seg = malloc(sizeof(*seg));
+    if (!seg) return NULL;
+
+    // 2. mmap 2MiB contiguous memory
+    seg->start = mmap(NULL, SMALL_MID_SEGMENT_SIZE,
+                      PROT_READ | PROT_WRITE,
+                      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
+    if (seg->start == MAP_FAILED) {
+        free(seg);
+        return NULL;
+    }
+
+    seg->total_size = SMALL_MID_SEGMENT_SIZE;
+    seg->page_size = SMALL_MID_PAGE_SIZE;
+    seg->num_pages = SMALL_MID_PAGES_PER_SEG;
+
+    // 3. Initialize per-class free page stacks
+    for (int i = 0; i < 8; i++) {
+        seg->free_pages[i] = NULL;
+        seg->free_count[i] = 0;
+        seg->current_page[i] = NULL;
+        seg->page_offset[i] = 0;
+    }
+
+    // 4. Allocate and initialize page metadata array
+    seg->pages = malloc(sizeof(SmallPageMeta*) * SMALL_MID_PAGES_PER_SEG);
+    if (!seg->pages) {
+        munmap(seg->start, SMALL_MID_SEGMENT_SIZE);
+        free(seg);
+        return NULL;
+    }
+
+    // Allocate individual page metadata structures
+    for (uint32_t i = 0; i < SMALL_MID_PAGES_PER_SEG; i++) {
+        SmallPageMeta *meta = malloc(sizeof(SmallPageMeta));
+        if (!meta) {
+            // Cleanup on failure
+            for (uint32_t j = 0; j < i; j++) {
+                free(seg->pages[j]);
+            }
+            free(seg->pages);
+            munmap(seg->start, SMALL_MID_SEGMENT_SIZE);
+            free(seg);
+            return NULL;
+        }
+
+        meta->ptr = (char*)seg->start + (i * SMALL_MID_PAGE_SIZE);
+        meta->capacity = 0;
+        meta->class_idx = 0xFF;  // Unassigned
+        meta->alloc_count = 0;
+        meta->free_count = 0;
+        meta->segment = seg;
+        meta->next = NULL;
+
+        seg->pages[i] = meta;
+    }
+
+    // 5. Register with RegionIdBox
+    seg->region_id = region_id_register_v6(seg->start, seg->total_size,
+                                           REGION_KIND_MID_V3, seg);
+
+    seg->total_allocations = 0;
+    seg->total_frees = 0;
+    seg->last_refill_count = 0;
+
+    return seg;
+}
+
+void small_segment_mid_v3_destroy(SmallSegment_MID_v3 *seg) {
+    if (!seg) return;
+
+    // Unregister from RegionIdBox
+    region_id_unregister_v6(seg->region_id);
+
+    // Free page metadata
+    if (seg->pages) {
+        for (uint32_t i = 0; i < SMALL_MID_PAGES_PER_SEG; i++) {
+            if (seg->pages[i]) {
+                free(seg->pages[i]);
+            }
+        }
+        free(seg->pages);
+    }
+
+    // Unmap segment memory
+    if (seg->start && seg->start != MAP_FAILED) {
+        munmap(seg->start, seg->total_size);
+    }
+
+    free(seg);
+}
+
+// ============================================================================
+// Page Management
+// ============================================================================
+
+// Take a page from the free stack (LIFO)
+void* small_segment_mid_v3_take_page(SmallSegment_MID_v3 *seg, uint32_t class_idx) {
+    if (!seg || class_idx >= 8) return NULL;
+
+    if (seg->free_count[class_idx] > 0) {
+        // Pop from free stack
+        void **stack = seg->free_pages[class_idx];
+        if (!stack || seg->free_count[class_idx] == 0) return NULL;
+
+        // Get the top page
+        void *page = stack[seg->free_count[class_idx] - 1];
+        seg->free_count[class_idx]--;
+
+        return page;
+    }
+
+    // No free pages available
+    return NULL;
+}
+
+// Release a page back to the free stack (LIFO)
+void small_segment_mid_v3_release_page(SmallSegment_MID_v3 *seg, void *page, uint32_t class_idx) {
+    if (!seg || !page || class_idx >= 8) return;
+
+    // Allocate stack if needed (lazy initialization)
+    if (!seg->free_pages[class_idx]) {
+        seg->free_pages[class_idx] = malloc(sizeof(void*) * SMALL_MID_PAGES_PER_SEG);
+        if (!seg->free_pages[class_idx]) return;
+    }
+
+    // Push to free stack
+    seg->free_pages[class_idx][seg->free_count[class_idx]] = page;
+    seg->free_count[class_idx]++;
+}
+
+// Get region ID
+uint32_t small_segment_mid_v3_region_id(SmallSegment_MID_v3 *seg) {
+    return seg ? seg->region_id : 0;
+}
+
+// Set region ID (called by RegionIdBox)
+void small_segment_mid_v3_set_region_id(SmallSegment_MID_v3 *seg, uint32_t region_id) {
+    if (seg) {
+        seg->region_id = region_id;
+    }
+}
+
+// Check if page is within segment bounds
+bool small_segment_mid_v3_contains_page(SmallSegment_MID_v3 *seg, void *page) {
+    if (!seg || !page) return false;
+
+    uintptr_t page_addr = (uintptr_t)page;
+    uintptr_t seg_start = (uintptr_t)seg->start;
+    uintptr_t seg_end = seg_start + seg->total_size;
+
+    return (page_addr >= seg_start && page_addr < seg_end);
+}
+
+// Get page metadata for pointer
+struct SmallPageMeta* small_segment_mid_v3_get_page_meta(
+    SmallSegment_MID_v3 *seg,
+    void *page
+) {
+    if (!seg || !page || !seg->pages) return NULL;
+
+    // Calculate page index
+    uintptr_t page_addr = (uintptr_t)page;
+    uintptr_t seg_start = (uintptr_t)seg->start;
+
+    if (page_addr < seg_start) return NULL;
+
+    uintptr_t offset = page_addr - seg_start;
+    uint32_t page_idx = offset / SMALL_MID_PAGE_SIZE;
+
+    if (page_idx >= SMALL_MID_PAGES_PER_SEG) return NULL;
+
+    return (struct SmallPageMeta*)seg->pages[page_idx];
+}
+
+// ============================================================================
+// Statistics
+// ============================================================================
+
+SmallSegmentStatsMID_v3 small_segment_mid_v3_get_stats(SmallSegment_MID_v3 *seg) {
+    SmallSegmentStatsMID_v3 stats = {0};
+
+    if (!seg) return stats;
+
+    stats.total_allocations = seg->total_allocations;
+    stats.total_frees = seg->total_frees;
+
+    // Count active pages per class
+    for (uint32_t i = 0; i < SMALL_MID_PAGES_PER_SEG; i++) {
+        SmallPageMeta *meta = seg->pages[i];
+        if (meta && meta->class_idx < 8 && meta->class_idx != 0xFF) {
+            stats.active_pages[meta->class_idx]++;
+        }
+    }
+
+    return stats;
+}
+
+void small_segment_mid_v3_reset_stats(SmallSegment_MID_v3 *seg) {
+    if (!seg) return;
+
+    seg->total_allocations = 0;
+    seg->total_frees = 0;
+    seg->last_refill_count = 0;
+}
+
+// ============================================================================
+// Validation & Debugging
+// ============================================================================
+
+bool small_segment_mid_v3_validate(SmallSegment_MID_v3 *seg) {
+    if (!seg) return false;
+    if (!seg->start || seg->start == MAP_FAILED) return false;
+    if (seg->total_size != SMALL_MID_SEGMENT_SIZE) return false;
+    if (seg->num_pages != SMALL_MID_PAGES_PER_SEG) return false;
+    if (!seg->pages) return false;
+
+    return true;
+}
+
+void small_segment_mid_v3_debug_print(SmallSegment_MID_v3 *seg) {
+    if (!seg) {
+        fprintf(stderr, "[MID_v3] Segment: NULL\n");
+        return;
+    }
+
+    fprintf(stderr, "[MID_v3] Segment %p:\n", (void*)seg);
+    fprintf(stderr, "  start=%p size=%zu pages=%u region_id=%u\n",
+            seg->start, seg->total_size, seg->num_pages, seg->region_id);
+    fprintf(stderr, "  allocs=%lu frees=%lu\n",
+            seg->total_allocations, seg->total_frees);
+
+    for (int i = 0; i < 8; i++) {
+        if (seg->free_count[i] > 0) {
+            fprintf(stderr, "  C%d: free_pages=%u\n", i, seg->free_count[i]);
+        }
+    }
+}
diff --git a/core/smallobject_stats_mid_v3.c b/core/smallobject_stats_mid_v3.c
new file mode 100644
index 00000000..02a77853
--- /dev/null
+++ b/core/smallobject_stats_mid_v3.c
@@ -0,0 +1,208 @@
+// smallobject_stats_mid_v3.c
+// Phase v11a-2: Stats collection for MID v3.5 page lifetime tracking
+
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include <time.h>
+#include "box/smallobject_stats_mid_v3_box.h"
+#include "box/smallobject_learner_v2_box.h"
+
+// ============================================================================
+// Helper: Get timestamp
+// ============================================================================
+
+static inline uint64_t get_timestamp_ns(void) {
+    struct timespec ts;
+    clock_gettime(CLOCK_MONOTONIC, &ts);
+    return (uint64_t)ts.tv_sec * 1000000000ULL + (uint64_t)ts.tv_nsec;
+}
+
+static inline uint64_t get_timestamp_ms(void) {
+    return get_timestamp_ns() / 1000000ULL;
+}
+
+// ============================================================================
+// Stats Context
+// ============================================================================
+
+typedef struct {
+    SmallPageStatsPublished_MID_v3 history[SMALL_STATS_HISTORY_SIZE];
+    uint64_t total_published;
+    uint32_t current_idx;
+    uint32_t eval_interval;
+    bool enabled;
+} SmallStatsContext_MID_v3;
+
+static SmallStatsContext_MID_v3 g_stats_ctx = {
+    .total_published = 0,
+    .current_idx = 0,
+    .eval_interval = SMALL_STATS_EVAL_INTERVAL,
+    .enabled = true
+};
+
+// ============================================================================
+// Stats Publishing
+// ============================================================================
+
+void small_stats_mid_v3_publish(const SmallPageStatsMID_v3 *stat) {
+    if (!stat || !g_stats_ctx.enabled) return;
+
+    SmallStatsContext_MID_v3 *ctx = &g_stats_ctx;
+
+    // Create published event
+    SmallPageStatsPublished_MID_v3 pub = {
+        .stat = *stat,
+        .page_ptr = NULL,
+        .retire_timestamp_ns = get_timestamp_ns(),
+        .sequence_number = ctx->total_published
+    };
+
+    // Store in history (circular buffer)
+    uint32_t idx = ctx->current_idx % SMALL_STATS_HISTORY_SIZE;
+    ctx->history[idx] = pub;
+    ctx->current_idx++;
+    ctx->total_published++;
+
+    // Periodic aggregation: notify Learner
+    if (ctx->total_published % ctx->eval_interval == 0) {
+        // Call Learner v2 to record this page stats
+        small_learner_v2_record_page_stats(stat);
+    }
+}
+
+const SmallPageStatsPublished_MID_v3* small_stats_mid_v3_latest(void) {
+    SmallStatsContext_MID_v3 *ctx = &g_stats_ctx;
+
+    if (ctx->total_published == 0) {
+        return NULL;
+    }
+
+    uint32_t idx = (ctx->current_idx - 1) % SMALL_STATS_HISTORY_SIZE;
+    return &ctx->history[idx];
+}
+
+uint64_t small_stats_mid_v3_published_count(void) {
+    return g_stats_ctx.total_published;
+}
+
+// ============================================================================
+// Periodic Aggregation
+// ============================================================================
+
+void small_stats_mid_v3_aggregate(SmallPageStatsAggregate_MID_v3 *out) {
+    if (!out) return;
+
+    memset(out, 0, sizeof(*out));
+    out->aggregate_timestamp_ns = get_timestamp_ns();
+
+    SmallStatsContext_MID_v3 *ctx = &g_stats_ctx;
+
+    // Aggregate from history (simple approach: aggregate last N events)
+    uint32_t count = ctx->total_published < SMALL_STATS_HISTORY_SIZE
+                     ? ctx->total_published
+                     : SMALL_STATS_HISTORY_SIZE;
+
+    for (uint32_t i = 0; i < count; i++) {
+        SmallPageStatsPublished_MID_v3 *pub = &ctx->history[i];
+        SmallPageStatsMID_v3 *stat = &pub->stat;
+
+        if (stat->class_idx < 8) {
+            out->class_allocations[stat->class_idx] += stat->total_allocations;
+            out->class_frees[stat->class_idx] += stat->total_frees;
+            out->class_retire_count[stat->class_idx]++;
+
+            // Weighted average for free hit ratio
+            uint64_t weight = stat->total_allocations;
+            if (weight > 0) {
+                out->class_avg_free_hit_bps[stat->class_idx] +=
+                    (stat->free_hit_ratio_bps * weight);
+            }
+        }
+
+        out->total_allocations += stat->total_allocations;
+        out->total_frees += stat->total_frees;
+        out->total_pages_retired++;
+    }
+
+    // Normalize weighted averages
+    for (int i = 0; i < 8; i++) {
+        if (out->class_allocations[i] > 0) {
+            out->class_avg_free_hit_bps[i] /= out->class_allocations[i];
+        }
+    }
+
+    if (out->total_allocations > 0) {
+        out->global_avg_free_hit_bps =
+            (out->total_frees * 10000) / out->total_allocations;
+    }
+
+    out->eval_count = ctx->total_published / ctx->eval_interval;
+}
+
+const SmallPageStatsAggregate_MID_v3* small_stats_mid_v3_aggregate_snapshot(void) {
+    static SmallPageStatsAggregate_MID_v3 snapshot;
+    small_stats_mid_v3_aggregate(&snapshot);
+    return &snapshot;
+}
+
+// ============================================================================
+// Configuration
+// ============================================================================
+
+void small_stats_mid_v3_set_eval_interval(uint32_t interval) {
+    g_stats_ctx.eval_interval = interval > 0 ? interval : SMALL_STATS_EVAL_INTERVAL;
+}
+
+uint32_t small_stats_mid_v3_get_eval_interval(void) {
+    return g_stats_ctx.eval_interval;
+}
+
+void small_stats_mid_v3_set_enabled(bool enabled) {
+    g_stats_ctx.enabled = enabled;
+}
+
+void small_stats_mid_v3_reset(void) {
+    memset(&g_stats_ctx, 0, sizeof(g_stats_ctx));
+    g_stats_ctx.eval_interval = SMALL_STATS_EVAL_INTERVAL;
+    g_stats_ctx.enabled = true;
+}
+
+// ============================================================================
+// Debugging & Monitoring
+// ============================================================================
+
+void small_stats_mid_v3_print_latest(void) {
+    const SmallPageStatsPublished_MID_v3 *pub = small_stats_mid_v3_latest();
+
+    if (!pub) {
+        fprintf(stderr, "[MID_v3_Stats] No stats published yet\n");
+        return;
+    }
+
+    const SmallPageStatsMID_v3 *stat = &pub->stat;
+    fprintf(stderr, "[MID_v3_Stats] Latest (seq=%lu):\n", pub->sequence_number);
+    fprintf(stderr, "  class_idx=%u allocs=%lu frees=%lu capacity=%u\n",
+            stat->class_idx, stat->total_allocations, stat->total_frees,
+            stat->page_alloc_count);
+    fprintf(stderr, "  free_hit_ratio=%u bps (%.2f%%)\n",
+            stat->free_hit_ratio_bps, stat->free_hit_ratio_bps / 100.0);
+}
+
+void small_stats_mid_v3_print_aggregate(void) {
+    const SmallPageStatsAggregate_MID_v3 *agg = small_stats_mid_v3_aggregate_snapshot();
+
+    fprintf(stderr, "[MID_v3_Stats] Aggregate:\n");
+    fprintf(stderr, "  total_allocations=%lu total_frees=%lu total_retires=%u\n",
+            agg->total_allocations, agg->total_frees, agg->total_pages_retired);
+    fprintf(stderr, "  global_avg_free_hit=%u bps (%.2f%%)\n",
+            agg->global_avg_free_hit_bps, agg->global_avg_free_hit_bps / 100.0);
+
+    for (int i = 0; i < 8; i++) {
+        if (agg->class_retire_count[i] > 0) {
+            fprintf(stderr, "  C%d: allocs=%lu frees=%lu retires=%u avg_hit=%u bps\n",
+                    i, agg->class_allocations[i], agg->class_frees[i],
+                    agg->class_retire_count[i], agg->class_avg_free_hit_bps[i]);
+        }
+    }
+}