Phase12 debug: restore SUPERSLAB constants/APIs, implement Box2 drain boundary, fix tiny_fast_pop to return BASE, honor TLS SLL toggle in alloc/free fast paths, add fail-fast stubs, and quiet capacity sentinel. Update CURRENT_TASK with A/B results (SLL-off stable; SLL-on crash).

core/hakmem_tiny_fastcache.inc.h

@@ -98,8 +98,8 @@ static inline __attribute__((always_inline)) void* tiny_fast_pop(int class_idx)
     } else {
         g_fast_count[class_idx] = 0;
     }
-    // Phase E1-CORRECT: All classes return user pointer (base+1)
-    return (void*)((uint8_t*)head + 1);
+    // Phase E1-CORRECT: Return BASE pointer; caller (HAK_RET_ALLOC) performs BASE→USER
+    return head;
 }
 
 static inline __attribute__((always_inline)) int tiny_fast_push(int class_idx, void* ptr) {