Phase 5 E4-1: Free Wrapper ENV Snapshot (+3.51% GO, ADOPTED)

Target: Consolidate free wrapper TLS reads (2→1)
- free() is 25.26% self% (top hot spot)
- Strategy: Apply E1 success pattern (ENV snapshot) to free path

Implementation:
- ENV gate: HAKMEM_FREE_WRAPPER_ENV_SNAPSHOT=0/1 (default 0)
- core/box/free_wrapper_env_snapshot_box.{h,c}: New box
  - Consolidates 2 TLS reads → 1 TLS read (50% reduction)
  - Reduces 4 branches → 3 branches (25% reduction)
  - Lazy init with probe window (bench_profile putenv sync)
- core/box/hak_wrappers.inc.h: Integration in free() wrapper
- Makefile: Add free_wrapper_env_snapshot_box.o to all targets

A/B Test Results (Mixed, 10-run, 20M iters):
- Baseline (SNAPSHOT=0): 45.35M ops/s (mean), 45.31M ops/s (median)
- Optimized (SNAPSHOT=1): 46.94M ops/s (mean), 47.15M ops/s (median)
- Improvement: +3.51% mean, +4.07% median

Decision: GO (+3.51% >= +1.0% threshold)
- Exceeded conservative estimate (+1.5% → +3.51%)
- Similar efficiency to E1 (+3.92%)
- Health check: PASS (all profiles)
- Action: PROMOTED to MIXED_TINYV3_C7_SAFE preset

Phase 5 Cumulative:
- E1 (ENV Snapshot): +3.92%
- E4-1 (Free Wrapper Snapshot): +3.51%
- Total Phase 4-5: ~+7.5%

E3-4 Correction:
- Phase 4 E3-4 (ENV Constructor Init): NO-GO / FROZEN
- Initial A/B showed +4.75%, but investigation revealed:
  - Branch prediction hint mismatch (UNLIKELY with always-true)
  - Retest confirmed -1.78% regression
  - Root cause: __builtin_expect(..., 0) with ctor_mode==1
- Decision: Freeze as research box (default OFF)
- Learning: Branch hints need careful tuning, TLS consolidation safer

Deliverables:
- docs/analysis/PHASE5_E4_FREE_GATE_OPTIMIZATION_1_DESIGN.md
- docs/analysis/PHASE5_E4_1_FREE_WRAPPER_ENV_SNAPSHOT_NEXT_INSTRUCTIONS.md
- docs/analysis/PHASE5_E4_2_MALLOC_WRAPPER_ENV_SNAPSHOT_NEXT_INSTRUCTIONS.md (next)
- docs/analysis/PHASE5_POST_E1_NEXT_INSTRUCTIONS.md
- docs/analysis/ENV_PROFILE_PRESETS.md (E4-1 added, E3-4 corrected)
- CURRENT_TASK.md (E4-1 complete, E3-4 frozen)
- core/bench_profile.h (E4-1 promoted to default)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docs/analysis/ENV_PROFILE_PRESETS.md

@@ -105,19 +105,25 @@ HAKMEM_ALLOC_GATE_SHAPE=1
 ```sh
 HAKMEM_ENV_SNAPSHOT=1
 ```
-  - **Status**: ✅ GO（Mixed 10-run: **+3.92% avg / +4.01% median**）→ default OFF（opt-in）
+  - **Status**: ✅ GO（Mixed 10-run: **+3.92% avg / +4.01% median**）→ ✅ Promoted to `MIXED_TINYV3_C7_SAFE` preset default（opt-out 可）
   - **Effect**: `tiny_c7_ultra_enabled_env/tiny_front_v3_enabled/tiny_metadata_cache_enabled` のホット ENV gate を snapshot 1 本に集約
   - **Rollback**: `HAKMEM_ENV_SNAPSHOT=0`
-- **Phase 4 E3-4（ENV Constructor Init）** ✅ GO (opt-in):
+- **Phase 4 E3-4（ENV Constructor Init）** ❌ NO-GO (FROZEN):
 ```sh
 # Requires E1
 HAKMEM_ENV_SNAPSHOT=1
 HAKMEM_ENV_SNAPSHOT_CTOR=1
 ```
-  - **Status**: ✅ GO（Mixed 10-run: **+4.75% mean / +4.35% median**）→ default OFF（opt-in）
-  - **Effect**: `hakmem_env_snapshot_enabled()` の lazy gate 判定を constructor init で短絡（hot path の分岐/ロード削減）
-  - **Note**: “constructor での pre-main init” を効かせたい場合は、プロセス起動前に ENV を設定する（bench_profile putenv だけでは遅い）
+  - **Status**: ❌ NO-GO（Mixed 10-run: **-1.44% mean / -1.03% median**）→ default OFF（freeze）
+  - **Reason**: constructor mode の gate 判定は “追加の分岐/ロード” になり、現状の hot path では得にならない
   - **Rollback**: `HAKMEM_ENV_SNAPSHOT_CTOR=0`
+- **Phase 5 E4-1（Free Wrapper ENV Snapshot）** ✅ GO (PROMOTION READY):
+```sh
+HAKMEM_FREE_WRAPPER_ENV_SNAPSHOT=1
+```
+  - **Status**: ✅ GO（Mixed 10-run: **+3.51% mean / +4.07% median**）→ ✅ Promoted to `MIXED_TINYV3_C7_SAFE` preset default（opt-out 可）
+  - **Effect**: `free()` wrapper の ENV 判定（複数 TLS read）を TLS snapshot 1 本に集約して early gate を短絡
+  - **Rollback**: `HAKMEM_FREE_WRAPPER_ENV_SNAPSHOT=0`
 - v2 系は触らない（C7_SAFE では Pool v2 / Tiny v2 は常時 OFF）。
 - FREE_POLICY/THP を触る実験例（現在の HEAD では必須ではなく、組み合わせによっては微マイナスになる場合もある）:
 ```sh