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/tiny_atomic.h

@@ -46,6 +46,15 @@ static inline uint32_t tiny_atomic_load_u32_acquire(_Atomic uint32_t* ptr) {
     return atomic_load_explicit(ptr, TINY_MO_ACQUIRE);
 }
 
+// Load uint8_t variant
+static inline uint8_t tiny_atomic_load_u8_relaxed(_Atomic uint8_t* ptr) {
+    return atomic_load_explicit(ptr, TINY_MO_RELAXED);
+}
+
+static inline uint8_t tiny_atomic_load_u8_acquire(_Atomic uint8_t* ptr) {
+    return atomic_load_explicit(ptr, TINY_MO_ACQUIRE);
+}
+
 // ========== Store Operations ==========
 
 // Store with explicit memory order