feat(server/pay): 优惠套餐(Promo SKU)每账号限购一次——已付过再下单 409 PROMO_ALREADY_USED

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01P9G7E3wmAYL9KeYCVZVsqu

server/internal/pay/handler_test.go

@@ -278,6 +278,84 @@ func TestGetOrder_EnrichedFields(t *testing.T) {
 	}
 }
 
+// 优惠档(Promo SKU)限购一次:已有 paid 台账 → 下单 409 PROMO_ALREADY_USED,
+// 且不打上游(fake pay client 一旦被调用即 t.Fatal)。
+func TestCreateOrder_PromoAlreadyUsed409(t *testing.T) {
+	router, st := newHandlerRig(t, func(w http.ResponseWriter, r *http.Request) {
+		t.Fatal("已购过优惠档,不该打到 pay 上游")
+	})
+	if err := st.Insert(context.Background(), 1, "uuid-1", "pro_month_promo", "promo-old", "alipay", 600, "CNY"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := st.db.ExecContext(context.Background(),
+		`UPDATE pay_purchases SET status = 'paid' WHERE out_trade_no = 'promo-old'`); err != nil {
+		t.Fatal(err)
+	}
+	body := []byte(`{"sku":"pro_month_promo","method":"alipay"}`)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, authed(httptest.NewRequest(http.MethodPost, "/v1/pay/orders", bytes.NewReader(body)), 1))
+	if w.Code != http.StatusConflict {
+		t.Fatalf("code = %d, body = %s", w.Code, w.Body)
+	}
+	var e struct {
+		Code string `json:"code"`
+	}
+	if err := json.Unmarshal(w.Body.Bytes(), &e); err != nil {
+		t.Fatal(err)
+	}
+	if e.Code != "PROMO_ALREADY_USED" {
+		t.Fatalf("code = %q, want PROMO_ALREADY_USED", e.Code)
+	}
+}
+
+// 优惠档历史只有 created/canceled(未 paid)→ 不受限,正常放行下单。
+func TestCreateOrder_PromoNotYetPaidAllowed(t *testing.T) {
+	router, st := newHandlerRig(t, func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte(`{"data":{"order_no":"promo-new","session":{
+			"render_type":"redirect","payload":{"url":"https://alipay.example/x"}}}}`))
+	})
+	if err := st.Insert(context.Background(), 1, "uuid-1", "pro_month_promo", "promo-created", "alipay", 600, "CNY"); err != nil {
+		t.Fatal(err)
+	}
+	if err := st.MarkCanceled(context.Background(), 1, "promo-created"); err != nil {
+		t.Fatal(err)
+	}
+	body := []byte(`{"sku":"pro_month_promo","method":"alipay"}`)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, authed(httptest.NewRequest(http.MethodPost, "/v1/pay/orders", bytes.NewReader(body)), 1))
+	if w.Code != http.StatusOK {
+		t.Fatalf("code = %d, body = %s", w.Code, w.Body)
+	}
+	row, err := st.GetForUser(context.Background(), 1, "promo-new")
+	if err != nil {
+		t.Fatalf("台账未落: %v", err)
+	}
+	if row.SKU != "pro_month_promo" || row.Status != "created" {
+		t.Fatalf("台账行不符: %+v", row)
+	}
+}
+
+// 非 promo SKU 即使已 paid 也不受限购约束(限购只针对 Promo==true 的 SKU)。
+func TestCreateOrder_NonPromoSKUUnlimited(t *testing.T) {
+	router, st := newHandlerRig(t, func(w http.ResponseWriter, r *http.Request) {
+		_, _ = w.Write([]byte(`{"data":{"order_no":"month-2","session":{
+			"render_type":"redirect","payload":{"url":"https://alipay.example/x"}}}}`))
+	})
+	if err := st.Insert(context.Background(), 1, "uuid-1", "pro_month", "month-1", "alipay", 2999, "CNY"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := st.db.ExecContext(context.Background(),
+		`UPDATE pay_purchases SET status = 'paid' WHERE out_trade_no = 'month-1'`); err != nil {
+		t.Fatal(err)
+	}
+	body := []byte(`{"sku":"pro_month","method":"alipay"}`)
+	w := httptest.NewRecorder()
+	router.ServeHTTP(w, authed(httptest.NewRequest(http.MethodPost, "/v1/pay/orders", bytes.NewReader(body)), 1))
+	if w.Code != http.StatusOK {
+		t.Fatalf("code = %d, body = %s", w.Code, w.Body)
+	}
+}
+
 func TestCatalog(t *testing.T) {
 	router, _ := newHandlerRig(t, nil)
 	w := httptest.NewRecorder()