feat(backend): pay 查单兜底适配 v2 订单八态 + 残单补查移出行锁事务

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

backend/internal/service/pay.go

@@ -285,7 +285,23 @@ func (s *PayService) replayed(nonce string) bool {
 
 // settle 入账：幂等（同 out_trade_no 只续一次）+ 金额核对（残单先兜底回填）+ 同事务续期。
 // webhook 与查单兜底共用此入口。
+//
+// 残单兜底（D1）的查单外呼是只读操作，不需要持行锁：调用方（webhook 签名负载 /
+// reconcile 自身查单结果）若已经带来非零金额，直接复用，不重复外呼 pay；只有调用方
+// 也不知道金额（amountMinor==0）时，才在事务外先轻量读一次购买单（无锁 First），
+// 若其 amount_minor 也是 0 才现查一次权威价。事务内仍以 FOR UPDATE 读到的行值为准做
+// 短路与核对，若行内金额仍为 0 才回填；补查失败/仍未知 → 核对不过 → ErrPayAmount（fail-closed）。
 func (s *PayService) settle(outTradeNo, bizCode string, amountMinor int64, currency, channel string, paidAt time.Time) error {
+	fillMinor, fillCurrency := amountMinor, currency
+	if fillMinor == 0 {
+		var pre model.LicensePurchase
+		if err := s.db.Where("out_trade_no = ?", outTradeNo).First(&pre).Error; err == nil && pre.AmountMinor == 0 {
+			if st, qerr := s.queryOrder(outTradeNo); qerr == nil && st.AmountMinor > 0 {
+				fillMinor, fillCurrency = st.AmountMinor, st.Currency
+			}
+		}
+	}
+
 	var shopID uint64
 	err := s.db.Transaction(func(tx *gorm.DB) error {
 		var p model.LicensePurchase
@@ -299,16 +315,14 @@ func (s *PayService) settle(outTradeNo, bizCode string, amountMinor int64, curre
 		if p.Status == "paid" { // 幂等：pay 会重发
 			return nil
 		}
-		if p.AmountMinor == 0 { // D1 残单兜底：下单后回填失败，入账前补查权威价
-			if st, qerr := s.queryOrder(outTradeNo); qerr == nil && st.AmountMinor > 0 {
-				p.AmountMinor, p.Currency = st.AmountMinor, st.Currency
-				if err := tx.Model(&model.LicensePurchase{}).Where("id = ?", p.ID).
-					Updates(map[string]any{"amount_minor": p.AmountMinor, "currency": p.Currency}).Error; err != nil {
-					return err
-				}
+		if p.AmountMinor == 0 && fillMinor > 0 { // 行内金额仍为 0 才回填，事务外查到的权威价直接落库
+			p.AmountMinor, p.Currency = fillMinor, fillCurrency
+			if err := tx.Model(&model.LicensePurchase{}).Where("id = ?", p.ID).
+				Updates(map[string]any{"amount_minor": p.AmountMinor, "currency": p.Currency}).Error; err != nil {
+				return err
 			}
 		}
-		if amountMinor != p.AmountMinor || !strings.EqualFold(currency, p.Currency) {
+		if p.AmountMinor == 0 || amountMinor != p.AmountMinor || !strings.EqualFold(currency, p.Currency) {
 			log.Printf("[pay] amount mismatch out_trade_no=%s purchase=%d/%s callback=%d/%s", outTradeNo, p.AmountMinor, p.Currency, amountMinor, currency)
 			return ErrPayAmount
 		}
@@ -532,26 +546,28 @@ func (s *PayService) reconcileOnce() {
 		if err != nil {
 			continue
 		}
-		// 状态语义暂沿用旧的三态判断（v2 八态 created|pending|paid|canceled|expired|
-		// refunding|partially_refunded|refunded 的完整适配留 Task 4）；这里仅做字段对齐保编译。
+		// v2 八态映射：created|pending 继续等；paid 入账续期；canceled|expired 标 failed
+		// （WHERE status='pending' 防竞态，webhook 可能已抢先入账）；退款三态本轮不冲权益，
+		// 仅记录（退款接入另起任务）。
 		switch st.Status {
 		case "paid":
 			paidAt := time.Now()
 			if st.PaidAt != nil {
 				paidAt = *st.PaidAt
 			}
+			// st.AmountMinor/st.Currency 已是本次查单拿到的权威价，settle 收到非 0 金额
+			// 不会再触发内部补查（见 settle 注释），此处查单只外呼一次。
 			if err := s.settle(p.OutTradeNo, p.ProductBizCode, st.AmountMinor, st.Currency, "", paidAt); err != nil {
 				log.Printf("[pay] reconcile settle failed out_trade_no=%s: %v", p.OutTradeNo, err)
 			} else {
 				log.Printf("[pay] reconcile settled out_trade_no=%s (webhook missed)", p.OutTradeNo)
 			}
-		case "closed":
+		case "canceled", "expired":
 			s.db.Model(&model.LicensePurchase{}).Where("id = ? AND status = 'pending'", p.ID).
 				Update("status", "failed")
-		case "refunded":
-			// 本轮不冲权益，仅记录（退款处理后续设计）
-			log.Printf("[pay] order refunded out_trade_no=%s (no-op)", p.OutTradeNo)
-		}
+		case "refunding", "partially_refunded", "refunded":
+			log.Printf("[pay] order %s status=%s (no-op，退款接入另起任务)", p.OutTradeNo, st.Status)
+		} // created/pending：继续等
 	}
 }