增加 sse服务端测试

test/OrderSupportTicket.TestServer/ApiException.cs

@@ -0,0 +1,18 @@
+namespace OrderSupportTicket.TestServer;
+
+/// <summary>
+/// 测试服务端主动返回的业务错误。中间件会转换为客户端可解析的 JSON。
+/// </summary>
+public sealed class ApiException : Exception
+{
+    public ApiException(int statusCode, string message, string code)
+        : base(message)
+    {
+        StatusCode = statusCode;
+        Code = code;
+    }
+
+    public int StatusCode { get; }
+
+    public string Code { get; }
+}