diff --git a/core/hakmem_tiny.c b/core/hakmem_tiny.c
index 8fdf0939..73538a95 100644
--- a/core/hakmem_tiny.c
+++ b/core/hakmem_tiny.c
@@ -113,28 +113,43 @@ static __thread unsigned char g_tls_bench_warm_done[4];
 // Return helper: record tiny alloc stat (guarded) then return pointer
 static inline void tiny_debug_track_alloc_ret(int cls, void* ptr);
 
-// Inject route commit into return helper so any successful allocation commits a fingerprint
-// CRITICAL FIX (Phase 7-1.3): Guard legacy macro to allow Phase 7 override
-// Phase 7 defines HAK_RET_ALLOC with header write in tiny_alloc_fast.inc.h
-#ifndef HAK_RET_ALLOC
-#ifdef HAKMEM_ENABLE_STATS
-// Optional: sampling（ビルド時に有効化）。ホットパスは直接インライン呼び出し（間接分岐なし）。
-#ifdef HAKMEM_TINY_STAT_SAMPLING
-static __thread unsigned g_tls_stat_accum_alloc[TINY_NUM_CLASSES];
-static int g_stat_rate_lg = 0;  // 0=毎回、それ以外=2^lgごと
-static inline __attribute__((always_inline)) void hkm_stat_alloc(int cls) {
-    if (__builtin_expect(g_stat_rate_lg == 0, 1)) { stats_record_alloc(cls); return; }
-    unsigned m = (1u << g_stat_rate_lg) - 1u;
-    if (((++g_tls_stat_accum_alloc[cls]) & m) == 0u) stats_record_alloc(cls);
-}
+// ========== HAK_RET_ALLOC: Single Definition Point ==========
+// Choose implementation based on HAKMEM_TINY_HEADER_CLASSIDX
+// - Phase 7 enabled: Write header and return user pointer
+// - Phase 7 disabled: Legacy behavior (stats + route + return)
+
+#if HAKMEM_TINY_HEADER_CLASSIDX
+    // Phase 7: Write class_idx to header before returning
+    #define HAK_RET_ALLOC(cls, ptr) return tiny_region_id_write_header((ptr), (cls))
 #else
-static inline __attribute__((always_inline)) void hkm_stat_alloc(int cls) { stats_record_alloc(cls); }
-#endif
-#define HAK_RET_ALLOC(cls, ptr) do { tiny_debug_track_alloc_ret((cls), (ptr)); hkm_stat_alloc((cls)); ROUTE_COMMIT((cls), 0x7F); return (ptr); } while(0)
-#else
-#define HAK_RET_ALLOC(cls, ptr) do { tiny_debug_track_alloc_ret((cls), (ptr)); ROUTE_COMMIT((cls), 0x7F); return (ptr); } while(0)
-#endif
-#endif  // HAK_RET_ALLOC
+    // Legacy: Stats and routing before return
+    #ifdef HAKMEM_ENABLE_STATS
+        // Optional: sampling（ビルド時に有効化）。ホットパスは直接インライン呼び出し（間接分岐なし）。
+        #ifdef HAKMEM_TINY_STAT_SAMPLING
+            static __thread unsigned g_tls_stat_accum_alloc[TINY_NUM_CLASSES];
+            static int g_stat_rate_lg = 0;  // 0=毎回、それ以外=2^lgごと
+            static inline __attribute__((always_inline)) void hkm_stat_alloc(int cls) {
+                if (__builtin_expect(g_stat_rate_lg == 0, 1)) { stats_record_alloc(cls); return; }
+                unsigned m = (1u << g_stat_rate_lg) - 1u;
+                if (((++g_tls_stat_accum_alloc[cls]) & m) == 0u) stats_record_alloc(cls);
+            }
+        #else
+            static inline __attribute__((always_inline)) void hkm_stat_alloc(int cls) { stats_record_alloc(cls); }
+        #endif
+        #define HAK_RET_ALLOC(cls, ptr) do { \
+            tiny_debug_track_alloc_ret((cls), (ptr)); \
+            hkm_stat_alloc((cls)); \
+            ROUTE_COMMIT((cls), 0x7F); \
+            return (ptr); \
+        } while(0)
+    #else
+        #define HAK_RET_ALLOC(cls, ptr) do { \
+            tiny_debug_track_alloc_ret((cls), (ptr)); \
+            ROUTE_COMMIT((cls), 0x7F); \
+            return (ptr); \
+        } while(0)
+    #endif
+#endif  // HAKMEM_TINY_HEADER_CLASSIDX
 
 // Free-side stats: compile-time zero when stats disabled
 #ifdef HAKMEM_ENABLE_STATS
diff --git a/core/tiny_alloc_fast.inc.h b/core/tiny_alloc_fast.inc.h
index 22a85611..88e77f67 100644
--- a/core/tiny_alloc_fast.inc.h
+++ b/core/tiny_alloc_fast.inc.h
@@ -63,13 +63,8 @@ extern int g_refill_count_hot;
 extern int g_refill_count_mid;
 extern int g_refill_count_class[TINY_NUM_CLASSES];
 
-// External macros
-// Phase 7: Write header before returning (if enabled)
-// CRITICAL: Undefine legacy macro to ensure Phase 7 version is used
-#ifdef HAK_RET_ALLOC
-#undef HAK_RET_ALLOC
-#endif
-#define HAK_RET_ALLOC(cls, ptr) return tiny_region_id_write_header((ptr), (cls))
+// HAK_RET_ALLOC macro is now defined in core/hakmem_tiny.c
+// See lines 116-152 for single definition point based on HAKMEM_TINY_HEADER_CLASSIDX
 
 // ========== RDTSC Profiling (lightweight) ==========
 #ifdef __x86_64__