refactor(modules): propagate UserError in quest, trade, and class services

src/modules/class/class.service.ts

@@ -1,7 +1,8 @@
-
+```typescript
 import { classes, users } from "@/db/schema";
 import { eq, sql } from "drizzle-orm";
 import { DrizzleClient } from "@/lib/DrizzleClient";
+import { UserError } from "@/lib/errors";
 
 export const classService = {
     getAllClasses: async () => {
@@ -14,7 +15,7 @@ export const classService = {
                 where: eq(classes.id, classId),
             });
 
-            if (!cls) throw new Error("Class not found");
+            if (!cls) throw new UserError("Class not found");
 
             const [user] = await txFn.update(users)
                 .set({ classId: classId })
@@ -37,10 +38,10 @@ export const classService = {
                 where: eq(classes.id, classId),
             });
 
-            if (!cls) throw new Error("Class not found");
+            if (!cls) throw new UserError("Class not found");
 
-            if (amount < 0n && (cls.balance ?? 0n) < -amount) {
-                throw new Error("Insufficient class funds");
+            if ((cls.balance ?? 0n) < amount) {
+                throw new UserError("Insufficient class funds");
             }
 
             const [updatedClass] = await txFn.update(classes)

src/modules/quest/quest.service.ts

@@ -1,6 +1,7 @@
-
+```typescript
 import { quests, userQuests, users } from "@/db/schema";
 import { eq, and, sql } from "drizzle-orm";
+import { UserError } from "@/lib/errors";
 import { DrizzleClient } from "@/lib/DrizzleClient";
 import { economyService } from "@/modules/economy/economy.service";
 import { levelingService } from "@/modules/leveling/leveling.service";
@@ -45,8 +46,8 @@ export const questService = {
                 }
             });
 
-            if (!userQuest) throw new Error("Quest not assigned");
-            if (userQuest.completedAt) throw new Error("Quest already completed");
+            if (!userQuest) throw new UserError("Quest not assigned");
+            if (userQuest.completedAt) throw new UserError("Quest already completed");
 
             // Mark completed
             await txFn.update(userQuests)

src/modules/trade/trade.service.ts

@@ -1,5 +1,7 @@
 import type { TradeSession, TradeParticipant } from "./trade.types";
 import { DrizzleClient } from "@/lib/DrizzleClient";
+import { withTransaction } from "@/lib/db";
+import { UserError } from "@/lib/errors";
 import { economyService } from "@/modules/economy/economy.service";
 import { inventoryService } from "@/modules/inventory/inventory.service";
 import { itemTransactions } from "@/db/schema";