diff --git a/backend/internal/service/pay.go b/backend/internal/service/pay.go
index 9d4effd..8e65c7f 100644
--- a/backend/internal/service/pay.go
+++ b/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
 	}
 }
 
diff --git a/backend/internal/service/pay_test.go b/backend/internal/service/pay_test.go
index 992211e..1573035 100644
--- a/backend/internal/service/pay_test.go
+++ b/backend/internal/service/pay_test.go
@@ -62,6 +62,16 @@ func createPendingPurchase(t *testing.T, db *gorm.DB, shopID uint64, bizCode str
 	return p
 }
 
+// createStalePendingPurchase 建一条 created_at 在 5 分钟对账窗口之外的 pending 购买单，
+// 供 reconcileOnce 测试（该函数只捞 created_at < now-5min 的 pending 单）。
+func createStalePendingPurchase(t *testing.T, db *gorm.DB, shopID uint64, bizCode string, amountMinor int64, currency, otn string) *model.LicensePurchase {
+	t.Helper()
+	p := createPendingPurchase(t, db, shopID, bizCode, amountMinor, currency, otn)
+	stale := time.Now().Add(-10 * time.Minute)
+	require.NoError(t, db.Model(&model.LicensePurchase{}).Where("id = ?", p.ID).Update("created_at", stale).Error)
+	return p
+}
+
 // ---------- 签名 ----------
 
 func TestPaySign_Vector(t *testing.T) {
@@ -164,6 +174,35 @@ func TestHandleCallback_ResidualAmountBackfill(t *testing.T) {
 	assert.NotNil(t, p.RenewedTo, "入账应落库续期后到期日")
 }
 
+// TestSettle_ResidualQueryFailFailsClosed：残单（amount_minor=0）且调用方自己也不知道金额
+// （amountMinor==0，如 reconcile 遇到 pay 侧字段异常）时，settle 内补查权威价若也失败
+// （pay 查单 500），必须 fail-closed：不入账、不续期、购买单维持 pending。
+func TestSettle_ResidualQueryFailFailsClosed(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PAY016")
+	createPendingPurchase(t, db, shop.ID, "annual_standard", 0, "", "yanmei-otn-residual-fail")
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("GET /api/v2/orders/yanmei-otn-residual-fail", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	})
+	payServer := httptest.NewServer(mux)
+	defer payServer.Close()
+
+	svc := newTestPaySvc(db, payServer.URL)
+	err := svc.settle("yanmei-otn-residual-fail", "annual_standard", 0, "", "alipay", time.Now())
+	assert.ErrorIs(t, err, ErrPayAmount, "补查也失败应 fail-closed")
+
+	var p model.LicensePurchase
+	require.NoError(t, db.Where("out_trade_no = ?", "yanmei-otn-residual-fail").First(&p).Error)
+	assert.Equal(t, "pending", p.Status, "补查失败不得入账")
+	assert.Nil(t, p.RenewedTo, "补查失败不得续期")
+
+	var licCount int64
+	require.NoError(t, db.Model(&model.License{}).Where("shop_id = ?", shop.ID).Count(&licCount).Error)
+	assert.Equal(t, int64(0), licCount, "补查失败不得续期")
+}
+
 // ---------- 回调：入账 ----------
 
 func TestHandleCallback_SettleAndRenew(t *testing.T) {
@@ -509,3 +548,101 @@ func TestBackfillPurchaseAmountMinor(t *testing.T) {
 	assert.Equal(t, int64(123), got3.AmountMinor, "已有 amount_minor>0 的行不被覆盖")
 	assert.Equal(t, "USD", got3.Currency, "已有 amount_minor>0 的行不被覆盖")
 }
+
+// ---------- 查单兜底：reconcileOnce v2 八态映射 ----------
+
+// reconcileMux 建一个只服务 GET /api/v2/orders/:no 的假 pay，固定返回给定状态/金额。
+func reconcileMux(t *testing.T, otn, status string, amountMinor int64, currency string) *httptest.Server {
+	t.Helper()
+	mux := http.NewServeMux()
+	mux.HandleFunc("GET /api/v2/orders/"+otn, func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprintf(w, `{"data":{"order_no":%q,"status":%q,"amount_minor":%d,"currency":%q}}`, otn, status, amountMinor, currency)
+	})
+	return httptest.NewServer(mux)
+}
+
+func TestReconcileOnce_PaidSettlesAndRenews(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PAY017")
+	createStalePendingPurchase(t, db, shop.ID, "annual_standard", 299900, "CNY", "yanmei-otn-reconcile-paid")
+
+	payServer := reconcileMux(t, "yanmei-otn-reconcile-paid", "paid", 299900, "CNY")
+	defer payServer.Close()
+
+	svc := newTestPaySvc(db, payServer.URL)
+	svc.reconcileOnce()
+
+	var p model.LicensePurchase
+	require.NoError(t, db.Where("out_trade_no = ?", "yanmei-otn-reconcile-paid").First(&p).Error)
+	assert.Equal(t, "paid", p.Status, "查单发现已支付应入账")
+	assert.NotNil(t, p.RenewedTo, "入账应同事务续期")
+
+	var lic model.License
+	require.NoError(t, db.Where("shop_id = ?", shop.ID).Order("id DESC").First(&lic).Error)
+	assert.InDelta(t, 365, daysFromNow(lic.ExpiresAt), 1, "年付套餐应续期 365 天")
+}
+
+func TestReconcileOnce_CanceledMarksFailed(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PAY018")
+	createStalePendingPurchase(t, db, shop.ID, "monthly_standard", 29900, "CNY", "yanmei-otn-reconcile-canceled")
+
+	payServer := reconcileMux(t, "yanmei-otn-reconcile-canceled", "canceled", 29900, "CNY")
+	defer payServer.Close()
+
+	svc := newTestPaySvc(db, payServer.URL)
+	svc.reconcileOnce()
+
+	var p model.LicensePurchase
+	require.NoError(t, db.Where("out_trade_no = ?", "yanmei-otn-reconcile-canceled").First(&p).Error)
+	assert.Equal(t, "failed", p.Status, "canceled 应标 failed")
+}
+
+func TestReconcileOnce_ExpiredMarksFailed(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PAY019")
+	createStalePendingPurchase(t, db, shop.ID, "monthly_standard", 29900, "CNY", "yanmei-otn-reconcile-expired")
+
+	payServer := reconcileMux(t, "yanmei-otn-reconcile-expired", "expired", 29900, "CNY")
+	defer payServer.Close()
+
+	svc := newTestPaySvc(db, payServer.URL)
+	svc.reconcileOnce()
+
+	var p model.LicensePurchase
+	require.NoError(t, db.Where("out_trade_no = ?", "yanmei-otn-reconcile-expired").First(&p).Error)
+	assert.Equal(t, "failed", p.Status, "expired 应标 failed")
+}
+
+func TestReconcileOnce_RefundedNoOp(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PAY020")
+	createStalePendingPurchase(t, db, shop.ID, "monthly_standard", 29900, "CNY", "yanmei-otn-reconcile-refunded")
+
+	payServer := reconcileMux(t, "yanmei-otn-reconcile-refunded", "refunded", 29900, "CNY")
+	defer payServer.Close()
+
+	svc := newTestPaySvc(db, payServer.URL)
+	svc.reconcileOnce()
+
+	var p model.LicensePurchase
+	require.NoError(t, db.Where("out_trade_no = ?", "yanmei-otn-reconcile-refunded").First(&p).Error)
+	assert.Equal(t, "pending", p.Status, "refunded 本轮 no-op，仅记录，状态不变")
+}
+
+// TestReconcileOnce_WithinWindowSkipped：created_at 未超 5 分钟对账窗口的 pending 单不应被捞到。
+func TestReconcileOnce_WithinWindowSkipped(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PAY021")
+	createPendingPurchase(t, db, shop.ID, "monthly_standard", 29900, "CNY", "yanmei-otn-reconcile-fresh")
+
+	payServer := reconcileMux(t, "yanmei-otn-reconcile-fresh", "paid", 29900, "CNY")
+	defer payServer.Close()
+
+	svc := newTestPaySvc(db, payServer.URL)
+	svc.reconcileOnce()
+
+	var p model.LicensePurchase
+	require.NoError(t, db.Where("out_trade_no = ?", "yanmei-otn-reconcile-fresh").First(&p).Error)
+	assert.Equal(t, "pending", p.Status, "未超窗口的单本轮不应被对账")
+}