Add finite prebattle shop stock

docs/DATA_MODEL.md

@@ -287,7 +287,7 @@ Weapon `range` also uses `[min, max]`. When class and equipment both provide ran
 
 Consumables use `kind: "consumable"` with effect records. `heal_hp` restores HP and `heal_mp` restores MP to a valid target; `Bean` and `Wine` are the first examples. Item use consumes the acting unit's action and only commits to the save file on victory. Weapons, armor, and accessories can be granted through `rewards.items`; they are shown in inventory, can be equipped through the Equip menu before the unit moves or acts, and are not usable from the battle item menu.
 
-Scenario `shop.items` controls which positive-price items appear in the current pre-battle shop. `shop.conditional_items` can append extra stock when saved campaign flags match. Purchases spend campaign gold, increment the campaign inventory count, save immediately, and then refresh the battle inventory copy if a scenario briefing is already loaded. The shop can also sell unequipped inventory stock back for 50% of base `price`, saving immediately and refreshing the loaded battle inventory copy. Later campaign data should add finite stock counts and unlock flags.
+Scenario `shop.items` controls which positive-price items appear in the current pre-battle shop. `shop.conditional_items` can append extra stock when saved campaign flags match. Entries can be plain item ids or objects with `id` and optional non-negative `stock`; `shop.stock` and conditional block `stock` objects can also set finite limits by item id. Items omitted from stock data are unlimited. Finite stock is tracked as per-scenario purchase counts in the campaign save, so buying an item decrements that scenario's remaining stock and manual checkpoint saves preserve it. Purchases spend campaign gold, increment the campaign inventory count, save immediately, and then refresh the battle inventory copy if a scenario briefing is already loaded. The shop can also sell unequipped inventory stock back for 50% of base `price`, saving immediately and refreshing the loaded battle inventory copy. Later campaign data should add broader unlock flags.
 
 The pre-battle Armory operates on the currently loaded player deployments and the copied battle inventory, then saves the changed roster entries and inventory counts back into `CampaignState`. Unlike in-battle equipment swaps, Armory changes persist immediately and survive defeat or restart. Completed-scenario replays keep Shop and Armory disabled so replay setup cannot alter the campaign save.
 
@@ -327,11 +327,13 @@ Scenario deployments may override `move_type` for special units. For example, a
     ]
   },
   "shop": {
-    "items": ["bean"],
+    "items": ["bean", { "id": "cloth_robe", "stock": 1 }],
+    "stock": { "bean": 3 },
     "conditional_items": [
       {
         "campaign_flags": { "regrouped_after_sishui": true },
-        "items": ["leather_armor"]
+        "items": ["training_spear", "leather_armor"],
+        "stock": { "leather_armor": 1 }
       }
     ]
   },
@@ -475,7 +477,7 @@ Event-spawned units use the same compact deployment shape as scenario starting u
 
 `scripts/core/data_catalog.gd` reads definition files once and `BattleState._apply_battle_data()` accepts either legacy `units` or catalog-backed `deployments`. Runtime units now carry `min_range`, `range`, `skills`, `exp`, `growth`, `growth_bonus`, and battle-only `status_effects` so the battle resolver can handle counterattacks, MP tactics, support buffs, enemy debuffs, EXP, level-ups, and enemy tactic AI without changing scenario files.
 
-`scripts/core/campaign_state.gd` writes `user://campaign_save.json` with `save_version`, completed scenarios, gold, inventory counts, joined officers, pending post-battle choice scenario id, applied post-battle choice ids, campaign flags, and player roster progression. The same snapshot can be copied to the one-slot manual checkpoint at `user://campaign_manual_save.json` from the pre-battle Save menu. Loading that checkpoint restores it into the active automatic save and then reloads the pending choice panel, campaign completion state, or current scenario briefing. Roster snapshots include level, EXP, stats, class id/name, class-derived movement/range/growth fields, skills, and equipment. Rewards, joined/left officers, and post-battle choices are guarded by completed scenario id so restarting a finished battle does not duplicate gold, items, membership changes, or branch decisions. On load, completed-scenario officer join/leave transitions are reconciled without replaying gold or item rewards, which lets new officer rewards added to older completed scenarios become available to existing saves.
+`scripts/core/campaign_state.gd` writes `user://campaign_save.json` with `save_version`, completed scenarios, gold, inventory counts, joined officers, pending post-battle choice scenario id, applied post-battle choice ids, campaign flags, per-scenario shop purchase counts, and player roster progression. The same snapshot can be copied to the one-slot manual checkpoint at `user://campaign_manual_save.json` from the pre-battle Save menu. Loading that checkpoint restores it into the active automatic save and then reloads the pending choice panel, campaign completion state, or current scenario briefing. Roster snapshots include level, EXP, stats, class id/name, class-derived movement/range/growth fields, skills, and equipment. Rewards, joined/left officers, and post-battle choices are guarded by completed scenario id so restarting a finished battle does not duplicate gold, items, membership changes, branch decisions, or finite shop purchases. On load, completed-scenario officer join/leave transitions are reconciled without replaying gold or item rewards, which lets new officer rewards added to older completed scenarios become available to existing saves.
 
 After a first-time victory, `CampaignState` advances `current_scenario_id` to the next entry in `data/campaign/campaign.json`. Completed-scenario replays return a result summary without rewriting the save or moving `current_scenario_id`. The battle scene passes `CampaignState.get_roster_overrides()`, `CampaignState.get_inventory_snapshot()`, `CampaignState.get_flags_snapshot()`, and `CampaignState.get_joined_officers_snapshot()` into `BattleState.load_battle()`, so officers can keep level/EXP/stat progression, equipped gear, consumable/equipment stock counts, recruitment gates, and branch flags into the next scenario.
 
@@ -485,7 +487,7 @@ During a battle, item consumption and equipment swaps affect `BattleState.battle
 
 Physical attacks grant normal attack/counter EXP only on hit after the attack/counter exchange resolves. A missed physical attack or counter grants a small miss EXP value, while defeat bonuses still require the attack to hit and defeat the target.
 
-Before a battle starts, `BattleScene` can buy priced items through `CampaignState.try_buy_item()` and sell unequipped inventory through `CampaignState.try_sell_item()`. Successful shop transactions update campaign gold and inventory in the save file immediately, then call `BattleState.set_inventory_snapshot()` so the upcoming battle sees the new stock. Pre-battle Armory changes call `CampaignState.try_save_prebattle_loadout()`, which merges the currently deployed roster snapshot into the saved roster and saves the adjusted inventory in the same operation. Pre-battle Roster calls `BattleState.try_set_unit_deployed()` to toggle optional player units while enforcing required officers and sortie limits. Pre-battle Formation calls `BattleState.try_set_prebattle_formation()`, which can move a player unit to an open formation cell or swap two player units inside the formation area. Roster and Formation choices are battle setup state, so the manual checkpoint stores campaign progression and saved loadout state but not unsaved sortie or starting-cell edits. Matching `briefing.conditional_lines` and `shop.conditional_items` are merged while the scenario loads, before the briefing panel opens. `post_battle_dialogue` is rendered by the battle scene after victory and before rewards/choices are shown in the result panel. Post-battle choices call `CampaignState.try_apply_post_battle_choice()`, which saves selected flags and rolls back flags, gold, and inventory if the save write fails.
+Before a battle starts, `BattleScene` can buy priced items through `CampaignState.try_buy_item()` and sell unequipped inventory through `CampaignState.try_sell_item()`. Successful shop transactions update campaign gold, inventory, and finite-stock purchase counts in the save file immediately, then call `BattleState.set_inventory_snapshot()` so the upcoming battle sees the new stock. Pre-battle Armory changes call `CampaignState.try_save_prebattle_loadout()`, which merges the currently deployed roster snapshot into the saved roster and saves the adjusted inventory in the same operation. Pre-battle Roster calls `BattleState.try_set_unit_deployed()` to toggle optional player units while enforcing required officers and sortie limits. Pre-battle Formation calls `BattleState.try_set_prebattle_formation()`, which can move a player unit to an open formation cell or swap two player units inside the formation area. Roster and Formation choices are battle setup state, so the manual checkpoint stores campaign progression and saved loadout state but not unsaved sortie or starting-cell edits. Matching `briefing.conditional_lines` and `shop.conditional_items` are merged while the scenario loads, before the briefing panel opens. `post_battle_dialogue` is rendered by the battle scene after victory and before rewards/choices are shown in the result panel. Post-battle choices call `CampaignState.try_apply_post_battle_choice()`, which saves selected flags and rolls back flags, gold, and inventory if the save write fails.
 
 When every campaign scenario id is present in `completed_scenarios`, the battle scene shows a campaign completion panel. Starting a new campaign clears the automatic save file and resets `current_scenario_id` to `start_scenario`; the manual checkpoint is left alone until overwritten from the Save menu.