Implement Phase 2: Headerless Allocator Support (Partial)

- Feature: Added HAKMEM_TINY_HEADERLESS toggle (A/B testing)
- Feature: Implemented Headerless layout logic (Offset=0)
- Refactor: Centralized layout definitions in tiny_layout_box.h
- Refactor: Abstracted pointer arithmetic in free path via ptr_conversion_box.h
- Verification: sh8bench passes in Headerless mode (No TLS_SLL_HDR_RESET)
- Known Issue: Regression in Phase 1 mode due to blind pointer conversion logic

core/box/tls_sll_box.h

@@ -368,6 +368,7 @@ static inline bool tls_sll_push_impl(int class_idx, hak_base_ptr_t ptr, uint32_t
     // Header restoration using Header Box (C1-C6 only; C0/C7 skip)
     // Safe mode (HAKMEM_TINY_SLL_SAFEHEADER=1): never overwrite header; reject on magic mismatch.
     // Default mode: restore expected header.
+#if !HAKMEM_TINY_HEADERLESS
     if (tiny_class_preserves_header(class_idx)) {
         static int g_sll_safehdr = -1;
         static int g_sll_ring_en = -1; // optional ring trace for TLS-SLL anomalies
@@ -407,6 +408,7 @@ static inline bool tls_sll_push_impl(int class_idx, hak_base_ptr_t ptr, uint32_t
             __atomic_thread_fence(__ATOMIC_RELEASE);
         }
     }
+#endif
 
     tls_sll_debug_guard(class_idx, ptr, "push");
 
@@ -568,6 +570,7 @@ static inline bool tls_sll_pop_impl(int class_idx, hak_base_ptr_t* out, const ch
     tls_sll_debug_guard(class_idx, base, "pop");
 
     // Header validation using Header Box (C1-C6 only; C0/C7 skip)
+#if !HAKMEM_TINY_HEADERLESS
     if (tiny_class_preserves_header(class_idx)) {
         uint8_t got, expect;
         PTR_TRACK_TLS_POP(raw_base, class_idx);
@@ -608,6 +611,7 @@ static inline bool tls_sll_pop_impl(int class_idx, hak_base_ptr_t* out, const ch
 #endif
         }
     }
+#endif
 
     // Read next via Box API.
     void* raw_next;