test(seed): prove a re-seed leaves five offers at the tuned numbers

The five offer tests this branch added all read the SHOP_OFFERS constant; none
ran the seed, so the one guarantee the stable-id design exists to provide --
re-seeding does not duplicate content -- was covered by nothing. This runs
`seedVisibleVerticalSlice` twice against an in-memory shop-offer repository and
asserts the five stable ids survive.

Confirmed catchable: reverting the conflict target to
['shopId', 'itemDefinitionId'] leaves 4 rows under the fake, because both bag
offers carry `itemDefinitionId: null` and collapse into one. On Postgres it
would fail outright.

The prices (12/30/40/35/60) and thresholds (reputation 25 and 40, renown 3) are
pinned in the same test: AGENTS.md §39 forbids silent rebalancing, and the
structural tests never looked at a number.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/api/src/database/seeds/vertical-slice.seed.spec.ts

@@ -20,7 +20,10 @@ import { NpcDefinition } from '../../npcs/entities/npc-definition.entity';
 import { NpcShop } from '../../shops/entities/npc-shop.entity';
 import { ShopOffer } from '../../shops/entities/shop-offer.entity';
 import { DEMO_CHARACTER_STARTING_WEAPON_ITEM_ID } from '../../demo/demo-character.constants';
-import { GameConditionType } from '../../conditions/game-condition.types';
+import {
+  ComparisonOperator,
+  GameConditionType,
+} from '../../conditions/game-condition.types';
 import {
   ASH_RAT_LOOT_TABLE_ID,
   CHARRED_LOOTER_LOOT_TABLE_ID,
@@ -29,7 +32,7 @@ import {
   WILD_ROAD_DOG_LOOT_TABLE_ID,
 } from './item.constants';
 import { BASIC_HIDE_BAG_ID } from './loot-bag-content';
-import { SHOP_OFFERS } from './npc-content';
+import { BORIN_OFFER_IDS, SHOP_OFFERS } from './npc-content';
 import { seedVisibleVerticalSlice } from './vertical-slice.seed';
 
 type Row = Record<string, unknown>;
@@ -956,4 +959,98 @@ describe('seedVisibleVerticalSlice', () => {
     expect(new Set(ids).size).toBe(ids.length);
     expect(ids.every((id) => id.length === 36)).toBe(true);
   });
+
+  it('still holds exactly five offers after a re-seed, at the tuned numbers', async () => {
+    const shopOfferRepository = new InMemoryRepository();
+    const dataSource = createDataSource(
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      new InMemoryRepository(),
+      shopOfferRepository,
+    );
+
+    // Twice, because that is the whole point of the stable ids (NPC spec §32).
+    // Both bag offers carry `itemDefinitionId: null`, so the pre-0.8.5 conflict
+    // target of (shopId, itemDefinitionId) would fold them into a single row
+    // here -- and would blow up outright on Postgres, where NULL never equals
+    // NULL in a unique index.
+    await seedVisibleVerticalSlice(dataSource);
+    await seedVisibleVerticalSlice(dataSource);
+
+    expect(shopOfferRepository.rows).toHaveLength(5);
+    expect(
+      shopOfferRepository.rows.map((row: Row) => String(row.id)).sort(),
+    ).toEqual(
+      [
+        BORIN_OFFER_IDS.potion,
+        BORIN_OFFER_IDS.shortsword,
+        BORIN_OFFER_IDS.trophyPouch,
+        BORIN_OFFER_IDS.hideBag,
+        BORIN_OFFER_IDS.banditBlade,
+      ].sort(),
+    );
+
+    // Prices and thresholds are balancing decisions, not incidentals, so a
+    // refactor must not be able to drift one silently (AGENTS.md §39).
+    const byId = new Map<string, Row>(
+      shopOfferRepository.rows.map((row: Row): [string, Row] => [
+        String(row.id),
+        row,
+      ]),
+    );
+    expect(byId.get(BORIN_OFFER_IDS.potion)).toMatchObject({
+      price: 12,
+      conditions: [],
+    });
+    expect(byId.get(BORIN_OFFER_IDS.shortsword)).toMatchObject({
+      price: 30,
+      conditions: [],
+    });
+    expect(byId.get(BORIN_OFFER_IDS.trophyPouch)).toMatchObject({
+      price: 40,
+      conditions: [
+        {
+          type: GameConditionType.REGION_REPUTATION,
+          key: 'border-guard',
+          operator: ComparisonOperator.GTE,
+          value: 25,
+        },
+      ],
+    });
+    expect(byId.get(BORIN_OFFER_IDS.hideBag)).toMatchObject({
+      price: 35,
+      conditions: [
+        {
+          type: GameConditionType.REGION_REPUTATION,
+          key: 'border-guard',
+          operator: ComparisonOperator.GTE,
+          value: 40,
+        },
+      ],
+    });
+    expect(byId.get(BORIN_OFFER_IDS.banditBlade)).toMatchObject({
+      price: 60,
+      conditions: [
+        {
+          type: GameConditionType.WORLD_RENOWN,
+          operator: ComparisonOperator.GTE,
+          value: 3,
+        },
+      ],
+    });
+  });
 });