diff --git a/CURRENT_TASK.md b/CURRENT_TASK.md
index 671944f4..ec53b563 100644
--- a/CURRENT_TASK.md
+++ b/CURRENT_TASK.md
@@ -1,253 +1,159 @@
-# Current Task: Phase 7 Task 5 - Comprehensive Benchmark Validation
+# Current Task: ACE Investigation - Mid-Large Performance Recovery
 
 **Date**: 2025-11-08
 **Status**: 🔄 IN PROGRESS
-**Priority**: HIGH
+**Priority**: CRITICAL
 
 ---
 
-## 🎉 Phase 7 Tasks 1-3: COMPLETE!
+## 🎉 Recent Achievements
 
-**Achievement**: **+180-280% Performance Improvement!** 🚀
+### 100% Stability Fix (Commit 616070cf7)
+- ✅ **50/50 consecutive 4T runs passed**
+- ✅ Bitmap semantics corrected (0xFFFFFFFF = full)
+- ✅ Race condition fixed with mutex protection
+- ✅ User requirement MET: "5%でもクラッシュおこったら使えない" → **0% crash rate**
 
-**Results (Quick Tests)**:
-- Random Mixed 128B: **59M ops/s** (92% of System) ✅
-- Random Mixed 256B: **70M ops/s** (90% of System) ✅
-- Random Mixed 512B: **68M ops/s** (85% of System) ✅
-- Random Mixed 1024B: **65M ops/s** (146% of System!) 🏆
-- Larson 1T: **2.68M ops/s** (stable) ✅
+### Comprehensive Benchmark Results (2025-11-08)
+Located at: `benchmarks/results/comprehensive_20251108_214317/`
 
-**Improvement vs Phase 6**: **+180-280%** 🚀
+**Performance Summary:**
 
-詳細: [`PHASE7_TASK3_RESULTS.md`](PHASE7_TASK3_RESULTS.md)
+| Category | HAKMEM | vs System | vs mimalloc | Status |
+|----------|--------|-----------|-------------|--------|
+| **Tiny Hot Path** | 218.65 M/s | **+48.5%** 🏆 | **+23.0%** 🏆 | **HUGE WIN** |
+| Random Mixed 128B | 16.92 M/s | 34% | 28% | Good (+3-4x from Phase 6) |
+| Random Mixed 256B | 17.59 M/s | 42% | 32% | Good |
+| Random Mixed 512B | 15.61 M/s | 42% | 33% | Good |
+| Random Mixed 2048B | 11.14 M/s | 50% | 65% | Competitive |
+| Random Mixed 4096B | 8.13 M/s | 61% | 66% | Competitive |
+| Larson 1T | 3.92 M/s | 28% | - | Needs work |
+| Larson 4T | 7.55 M/s | 45% | - | Needs work |
+| **Mid-Large MT** | 1.05 M/s | **-88%** 🔴 | **-86%** 🔴 | **CRITICAL ISSUE** |
+
+**Key Findings:**
+1. ✅ **First time beating BOTH System and mimalloc** (Tiny Hot Path)
+2. ✅ **100% stability** - All benchmarks passed without crashes
+3. 🔴 **Critical regression**: Mid-Large MT performance collapsed (-88%)
 
 ---
 
-## Objective: Task 5 - Comprehensive Validation
+## Objective: Investigate ACE for Mid-Large Performance Recovery
 
-包括的ベンチマークスイートを実行して、Phase 7 の改善を検証し、本番環境デプロイのベースラインを確立する。
+**Problem:**
+- Mid-Large MT: 1.05M ops/s (was +171% in docs, now -88%)
+- Root cause (from Task Agent report):
+  - ACE disabled → all mid allocations go to mmap (slow)
+  - This used to be HAKMEM's strength
+
+**Goal:**
+- Understand why ACE is disabled
+- Determine if re-enabling ACE can recover performance
+- If yes, implement ACE enablement
+- If no, find alternative optimization
+
+**Note:** HAKX is legacy code, ignore it. Focus on ACE mechanism.
 
 ---
 
-## Task Breakdown
+## Task for Task Agent (Ultrathink Required)
 
-### 1. 包括的ベンチマークスイート実行 (HIGH Priority)
+### Investigation Scope
 
-**Build Phase 7 最適化版**:
-```bash
-make clean
-make HEADER_CLASSIDX=1 AGGRESSIVE_INLINE=1 PREWARM_TLS=1 \
-  bench_comprehensive_hakmem \
-  bench_fragment_stress_hakmem \
-  larson_hakmem \
-  bench_random_mixed_hakmem
-```
+1. **ACE Current State**
+   - Why is ACE disabled?
+   - What does ACE do? (Adaptive Cache Engine)
+   - How does it help Mid-Large allocations?
 
-**実行するベンチマーク**:
+2. **Code Analysis**
+   - Find ACE enablement flags
+   - Find ACE initialization code
+   - Find ACE allocation path
+   - Understand ACE vs mmap decision
 
-#### 1.1 Comprehensive Benchmark (21 patterns × 4 sizes)
-```bash
-./bench_comprehensive_hakmem
-# 実行時間: ~5分
-# カバー範囲: LIFO, FIFO, Random, Interleaved, Long/Short-lived, Mixed
-# サイズ: 16B, 32B, 64B, 128B
-```
+3. **Root Cause**
+   - Why does disabling ACE cause -88% regression?
+   - What is the overhead of mmap for every allocation?
+   - Can we fix this by re-enabling ACE?
 
-**期待結果**:
-- Phase 6: -61.3% (52.59 M/s vs 135.94 M/s)
-- Phase 7: **85-92%** (目標達成!)
+4. **Proposed Solution**
+   - If ACE can be safely re-enabled: How?
+   - If ACE has bugs: What needs fixing?
+   - Alternative optimizations if ACE is not viable
 
-#### 1.2 Fragmentation Stress Test
-```bash
-./bench_fragment_stress_hakmem 50 2000
-# 実行時間: ~2分
-# テスト: 50ラウンド, 2000スロット, 混合サイズ
-```
-
-**期待結果**:
-- Phase 6: -75.0% (4.68 M/s vs 18.43 M/s)
-- Phase 7: **大幅改善** (TLS キャッシュ事前ウォームで)
-
-#### 1.3 Larson Multi-Thread Stress
-```bash
-# 1 thread (ベースライン)
-./larson_hakmem 1 1 128 1024 1 12345 1
-# 期待: 2.68M ops/s ✅
-
-# 2 threads
-./larson_hakmem 2 8 128 1024 1 12345 2
-
-# 4 threads
-./larson_hakmem 4 8 128 1024 1 12345 4
-
-# 8 threads (ストレス)
-./larson_hakmem 8 8 128 1024 1 12345 8
-```
-
-**期待結果**:
-- 1T: 2.68M ops/s (安定)
-- 4T: スケール確認 (デグレなし)
-
-#### 1.4 Random Mixed (各サイズ)
-```bash
-# Tiny range
-./bench_random_mixed_hakmem 100000 16 1234567
-./bench_random_mixed_hakmem 100000 32 1234567
-./bench_random_mixed_hakmem 100000 64 1234567
-./bench_random_mixed_hakmem 100000 128 1234567
-./bench_random_mixed_hakmem 100000 256 1234567
-./bench_random_mixed_hakmem 100000 512 1234567
-./bench_random_mixed_hakmem 100000 1024 1234567
-
-# Mid range (mid_mt territory)
-./bench_random_mixed_hakmem 100000 2048 1234567
-./bench_random_mixed_hakmem 100000 4096 1234567
-./bench_random_mixed_hakmem 100000 8192 1234567
-./bench_random_mixed_hakmem 100000 16384 1234567
-```
-
-**期待結果**:
-- Tiny (≤1KB): **85-92% of System**
-- Mid (1-8KB): **146% of System** (1024B)
-- Mid-Large (8-32KB): **+87% vs System** (既存 mid_mt)
-
-#### 1.5 長時間実行（安定性確認）
-```bash
-# 10倍長時間実行で安定結果
-./bench_random_mixed_hakmem 1000000 128 1234567
-./bench_random_mixed_hakmem 1000000 256 1234567
-./bench_random_mixed_hakmem 1000000 1024 1234567
-```
-
-**期待結果**:
-- 分散 ≤10% (安定性確認)
-- 平均値がクイックテストと一致
+5. **Implementation Plan**
+   - Step-by-step plan to recover Mid-Large performance
+   - Estimated effort (days)
+   - Risk assessment
 
 ---
 
-### 2. System malloc との比較
+## Success Criteria
 
-**System malloc 版をビルド**:
+✅ **Understand ACE mechanism and current state**
+✅ **Identify why Mid-Large performance collapsed**
+✅ **Propose concrete solution with implementation plan**
+✅ **Return detailed analysis report**
+
+---
+
+## Context for Task Agent
+
+**Current Build Flags:**
 ```bash
-make bench_comprehensive_system \
-     bench_fragment_stress_system \
-     bench_random_mixed_system
+make HEADER_CLASSIDX=1 AGGRESSIVE_INLINE=1 PREWARM_TLS=1
 ```
 
-**並行比較実行**:
-```bash
-# 両方実行して比較
-./bench_comprehensive_hakmem > results_hakmem.txt
-./bench_comprehensive_system > results_system.txt
+**Relevant Files to Check:**
+- `core/hakmem_ace*.c` - ACE implementation
+- `core/hakmem_mid_mt.c` - Mid-Large allocator
+- `core/hakmem_learner.c` - Learning mechanism
+- Build flags in Makefile
 
-# 比較レポート生成
-diff -y results_hakmem.txt results_system.txt
+**Benchmark to Verify:**
+```bash
+# Mid-Large MT (currently broken)
+./bench_mid_large_mt_hakmem
+# Expected: Should improve significantly with ACE
 ```
 
 ---
 
-### 3. Phase 6 からの性能後退チェック
+## Deliverables
 
-**Phase 6 ベースライン**:
-- Tiny: 21M ops/s (31% of System)
-- Mid-Large: 97M ops/s (+87% vs System)
+1. **ACE Analysis Report** (markdown)
+   - ACE mechanism explanation
+   - Current state diagnosis
+   - Root cause of -88% regression
+   - Proposed solution
 
-**Phase 7 期待値**:
-- Tiny: 59M ops/s (92% of System) ← **+181%** 🚀
-- Mid-Large: 97M ops/s (変化なし) ← 影響なし ✅
+2. **Implementation Plan**
+   - Concrete steps to fix
+   - Code changes needed
+   - Testing strategy
 
-**確認項目**:
-- ✅ Tiny が大幅改善
-- ✅ Mid-Large が維持
-- ✅ クラッシュなし
+3. **Risk Assessment**
+   - Stability impact
+   - Performance trade-offs
+   - Alternative approaches
 
 ---
 
-### 4. 成果物
+## Timeline
 
-**包括的レポート作成**:
-- `PHASE7_COMPREHENSIVE_BENCHMARK_RESULTS.md`
-- 全ベンチマーク結果
-- 比較表 (HAKMEM vs System)
-- 性能グラフ (可能なら)
-- 安定性分析 (分散、外れ値)
-- 本番環境準備度評価
-
-**ドキュメント更新**:
-- `CLAUDE.md` - 包括的結果セクション追加
-- `README.md` - 性能主張を更新
-- `benchmarks/results/` - 詳細結果をアーカイブ
+- **Investigation**: Task Agent (Ultrathink mode)
+- **Report Review**: 30 min
+- **Implementation**: 1-2 days (depends on findings)
+- **Validation**: Re-run benchmarks
 
 ---
 
-## 成功基準
+## Notes
 
-✅ **全ベンチマーククラッシュなく完了**
-✅ **Tiny 性能: 85-92% of System** (目標: 40-55%)
-✅ **Mid-Large 性能: 維持または改善**
-✅ **マルチスレッド安定性: 後退なし**
-✅ **フラグメンテーションストレス: 許容可能な性能**
-✅ **包括的レポート生成完了**
+- Debug logs now properly guarded with `HAKMEM_SUPERSLAB_VERBOSE`
+- Can be enabled with `-DHAKMEM_SUPERSLAB_VERBOSE` for debugging
+- Release builds will be clean (no log spam)
 
 ---
 
-## タイムライン
-
-- **ベンチマーク実行**: 1-2時間 (自動化)
-- **分析とレポート**: 2-3時間
-- **合計**: 4-5時間
-
----
-
-## 検証後の次のステップ
-
-**ベンチマーク合格の場合**:
-1. Task 6-9 (本番環境強化) に進む
-2. Task 4 (PGO) を検討 (最終 +3-5% ブースト)
-3. 本番環境デプロイ準備
-
-**問題発見の場合**:
-1. 性能後退を調査
-2. 修正して再テスト
-3. 既知の制限をドキュメント化
-
----
-
-## 備考
-
-- `HAKMEM_LOG=1` で詳細な初期化ログ
-- `valgrind --tool=massif` でメモリ使用量監視
-- `valgrind --leak-check=full` でメモリリークチェック
-- `perf record -g` でホットパスプロファイル
-
----
-
-## 📋 実行コマンドまとめ
-
-```bash
-# ビルド
-make clean
-make HEADER_CLASSIDX=1 AGGRESSIVE_INLINE=1 PREWARM_TLS=1 \
-  bench_comprehensive_hakmem larson_hakmem bench_random_mixed_hakmem
-
-# クイック検証 (5分)
-./bench_comprehensive_hakmem
-./larson_hakmem 1 1 128 1024 1 12345 1
-./bench_random_mixed_hakmem 100000 128 1234567
-
-# 完全検証 (1-2時間)
-for size in 16 32 64 128 256 512 1024 2048 4096 8192; do
-  echo "=== Size: $size ==="
-  ./bench_random_mixed_hakmem 100000 $size 1234567
-done
-
-./larson_hakmem 4 8 128 1024 1 12345 4
-./bench_fragment_stress_hakmem 50 2000
-
-# レポート生成
-# (結果を PHASE7_COMPREHENSIVE_BENCHMARK_RESULTS.md にまとめる)
-```
-
----
-
-**Status**: Task Agent に自動ベンチマーク実行を委譲する準備完了 🤖
+**Status**: Ready to launch Task Agent investigation 🚀
diff --git a/core/hakmem_tiny_superslab.c b/core/hakmem_tiny_superslab.c
index be291f32..23fb2e5e 100644
--- a/core/hakmem_tiny_superslab.c
+++ b/core/hakmem_tiny_superslab.c
@@ -564,11 +564,13 @@ int expand_superslab_head(SuperSlabHead* head) {
     // Allocate new chunk via existing superslab_allocate
     SuperSlab* new_chunk = superslab_allocate(head->class_idx);
     if (!new_chunk) {
+#if !defined(NDEBUG) || defined(HAKMEM_SUPERSLAB_VERBOSE)
         extern __thread int g_hakmem_lock_depth;
         g_hakmem_lock_depth++;
         fprintf(stderr, "[HAKMEM] CRITICAL: Failed to allocate new chunk for class %d (system OOM)\n",
                 head->class_idx);
         g_hakmem_lock_depth--;
+#endif
         return -1;  // True OOM (system out of memory)
     }
 
@@ -607,11 +609,13 @@ int expand_superslab_head(SuperSlabHead* head) {
 
     pthread_mutex_unlock(&head->expansion_lock);
 
+#if !defined(NDEBUG) || defined(HAKMEM_SUPERSLAB_VERBOSE)
     extern __thread int g_hakmem_lock_depth;
     g_hakmem_lock_depth++;
     fprintf(stderr, "[HAKMEM] Expanded SuperSlabHead for class %d: %zu chunks now (bitmap=0x%08x)\n",
             head->class_idx, new_count, new_chunk->slab_bitmap);
     g_hakmem_lock_depth--;
+#endif
 
     return 0;
 }
diff --git a/core/tiny_superslab_alloc.inc.h b/core/tiny_superslab_alloc.inc.h
index b866c059..cd277377 100644
--- a/core/tiny_superslab_alloc.inc.h
+++ b/core/tiny_superslab_alloc.inc.h
@@ -180,11 +180,13 @@ static SuperSlab* superslab_refill(int class_idx) {
             }
         } else {
             // Current chunk exhausted (all slabs occupied), try to expand
+#if !defined(NDEBUG) || defined(HAKMEM_SUPERSLAB_VERBOSE)
             extern __thread int g_hakmem_lock_depth;
             g_hakmem_lock_depth++;
             fprintf(stderr, "[HAKMEM] SuperSlab chunk exhausted for class %d (bitmap=0x%08x), expanding...\n",
                     class_idx, current_chunk->slab_bitmap);
             g_hakmem_lock_depth--;
+#endif
 
             // Protect expansion with global lock (race condition fix)
             static pthread_mutex_t expand_lock = PTHREAD_MUTEX_INITIALIZER;
@@ -199,15 +201,19 @@ static SuperSlab* superslab_refill(int class_idx) {
                 // Still exhausted, expand now
                 if (expand_superslab_head(head) < 0) {
                     pthread_mutex_unlock(&expand_lock);
+#if !defined(NDEBUG) || defined(HAKMEM_SUPERSLAB_VERBOSE)
                     g_hakmem_lock_depth++;
                     fprintf(stderr, "[HAKMEM] CRITICAL: Failed to expand SuperSlabHead for class %d (system OOM)\n", class_idx);
                     g_hakmem_lock_depth--;
+#endif
                     return NULL;  // True system OOM
                 }
 
+#if !defined(NDEBUG) || defined(HAKMEM_SUPERSLAB_VERBOSE)
                 g_hakmem_lock_depth++;
                 fprintf(stderr, "[HAKMEM] Successfully expanded SuperSlabHead for class %d\n", class_idx);
                 g_hakmem_lock_depth--;
+#endif
             }
 
             // Update current_chunk and tls->ss to point to (potentially new) chunk
@@ -219,9 +225,11 @@ static SuperSlab* superslab_refill(int class_idx) {
             full_mask = (ss_slabs_capacity(current_chunk) >= 32) ? 0xFFFFFFFF :
                         ((1U << ss_slabs_capacity(current_chunk)) - 1);
             if (!current_chunk || current_chunk->slab_bitmap == full_mask) {
+#if !defined(NDEBUG) || defined(HAKMEM_SUPERSLAB_VERBOSE)
                 g_hakmem_lock_depth++;
                 fprintf(stderr, "[HAKMEM] CRITICAL: Chunk still has no free slabs for class %d after expansion\n", class_idx);
                 g_hakmem_lock_depth--;
+#endif
                 return NULL;
             }
         }