Boxify superslab registry, add bench profile, and document C7 hotpath experiments

core/hakmem_shared_pool.c

@@ -7,6 +7,7 @@
 #include "box/tls_sll_drain_box.h"        // Box TLS SLL Drain (tiny_tls_sll_drain)
 #include "box/tls_slab_reuse_guard_box.h" // Box TLS Slab Reuse Guard (P0.3)
 #include "hakmem_policy.h"                // FrozenPolicy (learning layer)
+#include "box/shared_pool_box.h"          // Logical cap for bench profile
 
 #include <stdlib.h>
 #include <string.h>
@@ -287,6 +288,7 @@ shared_pool_init(void)
 {
     // Idempotent init; safe to call from multiple early paths.
     // pthread_mutex_t with static initializer is already valid.
+    shared_pool_box_init(NULL, NULL);
     pthread_mutex_lock(&g_shared_pool.alloc_lock);
     if (g_shared_pool.capacity == 0 && g_shared_pool.slabs == NULL) {
         shared_pool_ensure_capacity_unlocked(16);