Phase 68: PGO training set diversification (seed/WS expansion)

Changes:
- scripts/box/pgo_fast_profile_config.sh: Expanded WS patterns (3→5) and seeds (1→3)
  for reduced overfitting and better production workload representativeness
- PERFORMANCE_TARGETS_SCORECARD.md: Phase 68 baseline promoted (61.614M = 50.93%)
- CURRENT_TASK.md: Phase 68 marked complete, Phase 67a (layout tax forensics) set Active

Results:
- 10-run verification: +1.19% vs Phase 66 baseline (GO, >+1.0% threshold)
- M1 milestone: 50.93% of mimalloc (target 50%, exceeded by +0.93pp)
- Stability: 10-run mean/median with <2.1% CV

🤖 Generated with Claude Code

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

docs/analysis/PHASE66_PGO_FAST_WITH_LTO_RESULTS.md

@@ -0,0 +1,45 @@
+# Phase 66: PGO (FAST minimal, GCC+LTO) — Results
+
+## TL;DR
+
+PGO は **GO**。`BENCH_MINIMAL` の Mixed 10-run で **+6.58%**（mean）を達成。
+
+## What changed
+
+- Makefile: `pgo-fast-*` の PGO ワークフローを追加（GCC + `-flto` を維持）
+- `scripts/box/pgo_tiny_profile_box.sh`: `PGO_CONFIG` 切替対応 + workload を `bash -lc` で実行
+- `scripts/box/pgo_fast_profile_config.sh`: FAST minimal 用の PGO 代表ワークロード（cleanenv 前提）
+- Makefile: `bench_tiny_hot_hakmem` を `$(TINY_BENCH_OBJS)` でリンク（LTO 時の未解決参照を解消）
+
+## A/B (Mixed 10-run, cleanenv)
+
+計測の正:
+- `scripts/run_mixed_10_cleanenv.sh`（`ITERS=20000000 WS=400`）
+- baseline: `bench_random_mixed_hakmem_minimal`
+- treatment: `bench_random_mixed_hakmem_minimal_pgo`
+
+結果（n=10）:
+- Baseline mean: `61.718839M ops/s` / median: `61.672012M ops/s`
+- PGO mean: `65.780056M ops/s` / median: `66.227247M ops/s`
+- Delta: **+6.58% mean** / **+7.38% median**
+
+Verdict: ✅ **GO**（build-level のため +1.0% 以上で十分）
+
+## Key lesson (important)
+
+PGO は **profile mismatch で簡単に NO-GO になる**。
+
+- NG 例: `bench_random_mixed_hakmem` を “直起動” で profile 収集
+  - preset/ENV が一致せず、`FASTLANE_DIRECT` 等が OFF のプロファイルが混ざる
+  - 結果: PGO が逆方向に最適化して -5% 級の regression になり得る
+- OK 例（本 Phase 66）: **cleanenv 経由で profile 収集**
+  - `scripts/box/pgo_fast_profile_config.sh` が `scripts/run_mixed_10_cleanenv.sh` を使う
+
+## How to reproduce
+
+```sh
+make pgo-fast-full
+```
+
+（手動手順は `docs/analysis/PHASE66_PGO_FAST_WITH_LTO_INSTRUCTIONS.md`）
+