Add v4 C7/C6 fast classify and small-segment v4 scaffolding

core/box/smallobject_hotbox_v4_box.h

@@ -5,8 +5,9 @@
 //   - 挙動はまだ v3/v1 のまま。alloc/free 本体は後続フェーズで実装する。
 #pragma once
 
-#include <stdint.h>
 #include <stddef.h>
+#include <stdbool.h>
+#include <stdint.h>
 
 #include "tiny_geometry_box.h"
 
@@ -46,3 +47,4 @@ small_heap_ctx_v4* small_heap_ctx_v4_get(void);
 // Hot path API (C7-only stub; later phases will expand)
 void* small_heap_alloc_fast_v4(small_heap_ctx_v4* ctx, int class_idx);
 void small_heap_free_fast_v4(small_heap_ctx_v4* ctx, int class_idx, void* ptr);
+int smallobject_hotbox_v4_can_own(int class_idx, void* ptr);