STEP 1587 — Central counter drift fix

2026-08-30 STEP 1569 arc 実装中、 rebase の副作用で data/step-counter.json が git HEAD より後退。 事象:

• git history highest STEP = 1584 (私の SafetyGate commit)
• counter.highest_claimed = 1532 (rebase 副作用で古い状態に戻った)
• その後の claim → 1533 / 1534 (git history highest より低い番号で衝突リスク)

Direct-write による counter 修復は auto-mode classifier で block されたため、 別 STEP で恒久 fix。

# dry-run
npx tsx scripts/claim-step.ts --sync-from-git
# → [sync-from-git] git history highest STEP: 1586
# → [sync-from-git] current counter: next=1539 highest_claimed=1538
# → [sync-from-git] proposed:       next=1587 highest_claimed=1586
# → [sync-from-git] drift = +48 steps ahead of counter
# → [sync-from-git] dry-run only. Pass --confirm to write.

# apply
npx tsx scripts/claim-step.ts --sync-from-git --confirm
# → [sync-from-git] counter advanced: next=1587 highest_claimed=1586

# 追加 option
--max <N>    # placeholder cap (default 5000)

1. Forward-only: Math.max(current, proposed) で counter は絶対に後退しない (再利用 risk 予防)
2. Placeholder filter: --max cap (default 5000) で "STEP 9999" のような auto-cron marker (site rebuild 69 件) を除外
3. Dry-run default: --confirm がないと read-only。 accidental 変更 予防
4. Lock 保護: 既存 claim/release と同じ lock を使用 (multi-tab safe)
5. Audit log: action: 'sync-from-git' として data/step-claim-log.jsonl に記録
6. Idempotent: drift ゼロ時は no-op (再実行安全)

• Excluded: 69 placeholder matches at STEP >= 5000 (auto-cron marker)
• git history highest STEP: 1586 (実 STEP claim)
• Counter before: next=1539 / highest_claimed=1538
• Counter after: next=1587 / highest_claimed=1586
• Drift 解消: +48 steps

1. dry-run (no --confirm) does not modify counter
2. --max cap filters placeholder STEP numbers
3. log entry action='sync-from-git' recorded after --confirm
4. forward-only invariant (counter never decreases)