Phase v5-1: SmallObject v5 C6-only route stub 接続

- tiny_route_env_box.h: TINY_ROUTE_SMALL_HEAP_V5 enum 追加、route snapshot で C6→v5 分岐
- malloc_tiny_fast.h: alloc/free switch に v5 case 追加（v1/pool fallback）
- smallobject_hotbox_v5.c: stub 実装（alloc は NULL 返却、free は no-op）
- smallobject_hotbox_v5_box.h: 関数 signature に ctx パラメータ追加
- Makefile: core/smallobject_hotbox_v5.o をリンクリストに追加
- ENV_PROFILE_PRESETS.md: v5-1 プリセット追記
- CURRENT_TASK.md: Phase v5-1 完了記録

**特性**:
- ENV: HAKMEM_SMALL_HEAP_V5_ENABLED=1 / HAKMEM_SMALL_HEAP_V5_CLASSES=0x40 で opt-in
- テスト結果: C6-heavy (v5 OFF 15.5M → v5 ON 16.4M ops/s, 正常), Mixed 47.2M ops/s, SEGV/assert なし
- 挙動は v1/pool fallback と同じ（実装は v5-2）

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

core/box/tiny_route_env_box.h

@@ -11,6 +11,7 @@
 
 #include "smallobject_hotbox_v3_env_box.h"
 #include "smallobject_hotbox_v4_env_box.h"
+#include "smallobject_v5_env_box.h"
 
 typedef enum {
     TINY_ROUTE_LEGACY = 0,
@@ -18,6 +19,7 @@ typedef enum {
     TINY_ROUTE_HOTHEAP_V2 = 2,       // TinyHotHeap v2
     TINY_ROUTE_SMALL_HEAP_V3 = 3,    // SmallObject HotHeap v3 (C7-first,研究箱)
     TINY_ROUTE_SMALL_HEAP_V4 = 4,    // SmallObject HotHeap v4 (stub, route未使用)
+    TINY_ROUTE_SMALL_HEAP_V5 = 5,    // SmallObject HotHeap v5 (C6-only route stub, Phase v5-1)
 } tiny_route_kind_t;
 
 extern tiny_route_kind_t g_tiny_route_class[TINY_NUM_CLASSES];
@@ -25,7 +27,10 @@ extern int g_tiny_route_snapshot_done;
 
 static inline void tiny_route_snapshot_init(void) {
     for (int i = 0; i < TINY_NUM_CLASSES; i++) {
-        if (small_heap_v4_class_enabled((uint8_t)i)) {
+        // Phase v5-1: C6-only v5 route stub (before v4 check)
+        if (i == 6 && small_heap_v5_class_enabled(6)) {
+            g_tiny_route_class[i] = TINY_ROUTE_SMALL_HEAP_V5;
+        } else if (small_heap_v4_class_enabled((uint8_t)i)) {
             g_tiny_route_class[i] = TINY_ROUTE_SMALL_HEAP_V4;
         } else if (small_heap_v3_class_enabled((uint8_t)i)) {
             g_tiny_route_class[i] = TINY_ROUTE_SMALL_HEAP_V3;
@@ -54,7 +59,8 @@ static inline int tiny_route_is_heap_kind(tiny_route_kind_t route) {
     return route == TINY_ROUTE_HEAP ||
            route == TINY_ROUTE_HOTHEAP_V2 ||
            route == TINY_ROUTE_SMALL_HEAP_V3 ||
-           route == TINY_ROUTE_SMALL_HEAP_V4;
+           route == TINY_ROUTE_SMALL_HEAP_V4 ||
+           route == TINY_ROUTE_SMALL_HEAP_V5;
 }
 
 // C7 front が TinyHeap を使うか（Route snapshot 経由で判定）