fix(c2c): 过期恢复时合并到已有PENDING订单，避免同maker产生重复挂单

原来每个过期的MATCHED子订单都创建独立PENDING，导致一个卖单被多人
部分接单后过期会产生多个重复挂单。现在恢复时先查找同maker/type/price
的PENDING订单，有则合并数量，无则创建新订单。

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/services/trading-service/src/application/services/c2c.service.ts

@@ -780,16 +780,50 @@ export class C2cService {
           },
         });
 
-        // 3. MATCHED/PAID 订单恢复为新的 PENDING 订单
+        // 3. MATCHED/PAID 订单恢复：优先合并到已有的同 maker/type/price 的 PENDING 订单
         if (shouldRestore) {
           const priceDecimal = new Decimal(freshOrder.price);
+
+          // 查找是否已有可合并的 PENDING 订单（同 maker + 同类型 + 同价格）
+          const existingPending = await tx.c2cOrder.findFirst({
+            where: {
+              makerAccountSequence: freshOrder.makerAccountSequence,
+              type: freshOrder.type as any,
+              status: C2C_ORDER_STATUS.PENDING as any,
+              price: freshOrder.price,
+            },
+          });
+
+          if (existingPending) {
+            // 合并到已有 PENDING 订单：增加数量和总金额
+            const existingQty = new Decimal(existingPending.quantity.toString());
+            const mergedQty = existingQty.plus(quantityDecimal);
+            const mergedTotal = priceDecimal.mul(mergedQty).toString();
+            restoreOrderNo = existingPending.orderNo;
+
+            this.logger.log(
+              `[EXPIRY][TX] 步骤3: 合并到已有 PENDING 订单 ${existingPending.orderNo}, ` +
+              `原数量=${existingQty} + 恢复=${quantityDecimal} = ${mergedQty}`,
+            );
+
+            await tx.c2cOrder.update({
+              where: { orderNo: existingPending.orderNo },
+              data: {
+                quantity: mergedQty.toString(),
+                totalAmount: mergedTotal,
+              },
+            });
+          } else {
+            // 无可合并订单，创建新的 PENDING 订单
             restoreOrderNo = this.generateOrderNo();
             const totalAmount = priceDecimal.mul(quantityDecimal).toString();
+
             this.logger.log(
-            `[EXPIRY][TX] 步骤3: 恢复为新 PENDING 订单 ${restoreOrderNo}, ` +
+              `[EXPIRY][TX] 步骤3: 创建新 PENDING 订单 ${restoreOrderNo}, ` +
               `类型=${freshOrder.type}, maker=${freshOrder.makerAccountSequence}, ` +
               `数量=${quantityDecimal}, 总金额=${totalAmount}`,
             );
+
             await tx.c2cOrder.create({
               data: {
                 orderNo: restoreOrderNo,
@@ -812,6 +846,7 @@ export class C2cService {
                 remark: freshOrder.remark,
               },
             });
+          }
         } else {
           this.logger.debug(`[EXPIRY][TX] 步骤3: PENDING 订单无需恢复`);
         }