test(backend): 补下单后查单失败金额留 0 的兜底分支用例

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

backend/internal/service/pay_test.go

@@ -278,6 +278,35 @@ func TestCreatePurchase_HappyPath(t *testing.T) {
 	assert.Equal(t, strconv.FormatUint(p.ID, 10), gotBizRef, "biz_ref 应为购买记录 id")
 }
 
+// TestCreatePurchase_QueryOrderFailKeepsZeroAmount 覆盖 D1 金额兜底：下单 POST 成功但
+// best-effort 查单 GET 失败时，不阻断下单，金额留 0（PayURL/OutTradeNo 等仍正常落库）。
+func TestCreatePurchase_QueryOrderFailKeepsZeroAmount(t *testing.T) {
+	db := testutil.SetupTestDB()
+	shop := testutil.CreateTestShop(db, "PAY007")
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("POST /api/v2/orders", func(w http.ResponseWriter, r *http.Request) {
+		fmt.Fprint(w, `{"data":{"order_no":"pay-test-qf","session":{"render_type":"redirect","payload":{"url":"https://pay.test/cashier"}}}}`)
+	})
+	mux.HandleFunc("GET /api/v2/orders/pay-test-qf", func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	})
+	payServer := httptest.NewServer(mux)
+	defer payServer.Close()
+
+	svc := newTestPaySvc(db, payServer.URL)
+	res, err := svc.CreatePurchase(shop.ID, 1, "annual_standard", "mobile")
+	require.NoError(t, err, "查单失败不应阻断下单")
+	assert.Equal(t, int64(0), res.AmountMinor, "查单失败金额留 0")
+	assert.Equal(t, "", res.Amount, "查单失败金额留 0")
+	assert.Equal(t, "https://pay.test/cashier", res.PayURL)
+
+	var p model.LicensePurchase
+	require.NoError(t, db.Where("out_trade_no = ?", "pay-test-qf").First(&p).Error)
+	assert.Equal(t, "https://pay.test/cashier", p.PayURL)
+	assert.Equal(t, int64(0), p.AmountMinor)
+}
+
 func TestCreatePurchase_UnknownPlanAndUnconfigured(t *testing.T) {
 	db := testutil.SetupTestDB()
 	svc := newTestPaySvc(db, "http://pay.invalid")