quests: QuestMetrics helpers (purchaseOffer/purchaseItem), README quests section

src/index.ts

@@ -27,6 +27,7 @@ export type {
 export type { LeaderboardsService, LeaderboardHandle } from './leaderboards/LeaderboardsService.js';
 export type { BattlePassService } from './battlepass/BattlePassService.js';
 export type { QuestsService } from './quests/QuestsService.js';
+export * as QuestMetrics from './quests/QuestMetrics.js';
 
 // Observable state primitives
 export { SyncedState } from './state/SyncedState.js';

src/quests/QuestMetrics.ts

@@ -0,0 +1,18 @@
+/**
+ * QuestMetrics — builders for the quest metric strings known to the platform.
+ *
+ * Purchase metrics are reported automatically by the shop purchase fan-out,
+ * so these helpers exist mainly to name the format instead of hardcoding it.
+ * Any other metric is a custom string reported via
+ * {@link QuestsService.reportProgress}.
+ */
+
+/** Metric for purchasing a store offer; auto-reported on purchase. */
+export function purchaseOffer(offerId: string): string {
+  return `purchase.offer:${offerId}`;
+}
+
+/** Metric for purchasing a catalog item; auto-reported on purchase. */
+export function purchaseItem(itemId: string): string {
+  return `purchase.item:${itemId}`;
+}