P06-01: Implement approved A06 finite Mana reserve (MP-01-r02 recommended)

Initial 100, capacity 300, world tree +20 per 10 game minutes. Each boundary
pays registered upkeep demand before storing surplus; overflow is discarded
and recorded, 0 stops the whole tower. Furnace offers are judged after
generation and demand payment. New saves carry mana_reserve and Operations
rollback includes it; legacy saves keep a 0..300 amount and reject others.

Outage tests that relied on Mana 0 persisting now hold the outage with a
disabled demand sink, since the world tree recovers at the next boundary.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/plans/original-completion-2026-10-02/decisions.json

@@ -33,6 +33,14 @@
       "decision": "2×1・裏層。建築350G、資材4、工期60分、清掃員最低1人／上限2人、顧客0人・利用料なし、維持費2G／日。清潔0〜100・初期100、75以下で予約、現地8分で25回復。定義済み汚れ量を使い未定義値を補完しない。",
       "origin": "user_reply",
       "reference": "../original-completion-2026-09-29/execution/CLEANING_APPROVED_FOUNDATION.md"
+    },
+    {
+      "id": "A06",
+      "title": "マナ有限残量契約（MP-01-r02推薦案）",
+      "decision": "初期100・容量300・世界樹生成20／ゲーム内10分。10分境界ごとにB+G+F−Dを計算し、需要を先に支払い、超過は明示破棄、0で全館停止。需要は登録済み全consumerのmaintenance_mana合計（閉店・停止中も計上）。炉の投入は自然生成と需要支払後のbase_after=min(C,max(0,B+G−D))で空き100以上のとき受理。現Runtimeのphase順序を保持しMANA内で処理。旧セーブの残量は0〜300のみ保持し、超過・不正値は拒否。炉の人物適格性・収率の実接続は別承認。",
+      "origin": "user_reply_in_conversation",
+      "approved_at_jst": "2026-10-19",
+      "reference": "execution/mana-proposal/PROPOSAL.md"
     }
   ],
   "pending": [