Phase 24-26: Hot path atomic telemetry prune (+2.00% cumulative)

Summary:
- Phase 24 (alloc stats): +0.93% GO
- Phase 25 (free stats): +1.07% GO
- Phase 26 (diagnostics): -0.33% NEUTRAL (code cleanliness)
- Total: 11 atomics compiled-out, +2.00% improvement

Phase 24: OBSERVE tax prune (tiny_class_stats_box.h)
- Added HAKMEM_TINY_CLASS_STATS_COMPILED (default: 0)
- Wrapped 5 stats functions: uc_miss, warm_hit, shared_lock, tls_carve_*
- Result: +0.93% (baseline 56.675M vs compiled-in 56.151M ops/s)

Phase 25: Tiny free stats prune (tiny_superslab_free.inc.h)
- Added HAKMEM_TINY_FREE_STATS_COMPILED (default: 0)
- Wrapped g_free_ss_enter atomic in free hot path
- Result: +1.07% (baseline 57.017M vs compiled-in 56.415M ops/s)

Phase 26: Hot path diagnostic atomics prune
- Added 5 compile gates for low-frequency error counters:
  - HAKMEM_TINY_C7_FREE_COUNT_COMPILED
  - HAKMEM_TINY_HDR_MISMATCH_LOG_COMPILED
  - HAKMEM_TINY_HDR_META_MISMATCH_COMPILED
  - HAKMEM_TINY_METRIC_BAD_CLASS_COMPILED
  - HAKMEM_TINY_HDR_META_FAST_COMPILED
- Result: -0.33% NEUTRAL (within noise, kept for cleanliness)

Alignment with mimalloc principles:
- "No atomics on hot path" - telemetry moved to compile-time opt-in
- Fixed per-op tax elimination
- Production builds: maximum performance (atomics compiled-out)
- Research builds: full diagnostics (COMPILED=1)

Generated with Claude Code
https://claude.com/claude-code

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

core/front/tiny_unified_cache.h

@@ -223,12 +223,15 @@ static inline int unified_cache_push(int class_idx, hak_base_ptr_t base) {
 
     void* base_raw = HAK_BASE_TO_RAW(base);
 
+#if HAKMEM_TINY_TCACHE_COMPILED
     // Phase 14 v1: Try tcache first (intrusive LIFO, no array access)
+    // Phase 22: Compile-out when disabled (default OFF)
     if (tiny_tcache_try_push(class_idx, base_raw)) {
         return 1;  // SUCCESS (tcache hit, no array access)
     }
+#endif
 
-    // Tcache overflow or disabled → fall through to array cache
+    // Tcache overflow/disabled/compiled-out → fall through to array cache
     TinyUnifiedCache* cache = &g_unified_cache[class_idx];  // 1 cache miss (TLS)
 
     // Phase 8-Step3: Lazy init check (conditional in PGO mode)
@@ -289,30 +292,36 @@ static inline hak_base_ptr_t unified_cache_pop_or_refill(int class_idx) {
     }
     #endif
 
+#if HAKMEM_TINY_TCACHE_COMPILED
     // Phase 14 v1: Try tcache first (intrusive LIFO, no array access)
+    // Phase 22: Compile-out when disabled (default OFF)
     void* tcache_base = tiny_tcache_try_pop(class_idx);
     if (tcache_base != NULL) {
 #if !HAKMEM_BUILD_RELEASE
         g_unified_cache_hit[class_idx]++;
 #endif
-        // Performance measurement: count cache hits (ENV enabled only)
+#if HAKMEM_TINY_UNIFIED_CACHE_MEASURE_COMPILED
+        // Phase 23: Performance measurement (compile-out when disabled, default OFF)
         if (__builtin_expect(unified_cache_measure_check(), 0)) {
             atomic_fetch_add_explicit(&g_unified_cache_hits_global,
                                       1, memory_order_relaxed);
             atomic_fetch_add_explicit(&g_unified_cache_hits_by_class[class_idx],
                                       1, memory_order_relaxed);
         }
+#endif
         return HAK_BASE_FROM_RAW(tcache_base);  // HIT (tcache, no array access)
     }
+#endif
 
-    // Tcache miss or disabled → try pop from array cache (fast path)
+    // Tcache miss/disabled/compiled-out → try pop from array cache (fast path)
     if (__builtin_expect(cache->head != cache->tail, 1)) {
         void* base = cache->slots[cache->head];  // 1 cache miss (array access)
         cache->head = (cache->head + 1) & cache->mask;
 #if !HAKMEM_BUILD_RELEASE
         g_unified_cache_hit[class_idx]++;
 #endif
-        // Performance measurement: count cache hits（ENV 有効時のみ）
+#if HAKMEM_TINY_UNIFIED_CACHE_MEASURE_COMPILED
+        // Phase 23: Performance measurement (compile-out when disabled, default OFF)
         if (__builtin_expect(unified_cache_measure_check(), 0)) {
             atomic_fetch_add_explicit(&g_unified_cache_hits_global,
                                       1, memory_order_relaxed);
@@ -320,6 +329,7 @@ static inline hak_base_ptr_t unified_cache_pop_or_refill(int class_idx) {
             atomic_fetch_add_explicit(&g_unified_cache_hits_by_class[class_idx],
                                       1, memory_order_relaxed);
         }
+#endif
         return HAK_BASE_FROM_RAW(base);  // Hit! (2-3 cache misses total)
     }