简单的修改

FATrace.OEMApp/Services/DownloadTaskWorker.cs

@@ -62,11 +62,12 @@ namespace FATrace.OEMApp.Services
                 var maxRetry = ConfigHelper.GetIntOrDefault("DownloadTaskMaxRetry", 3);
                 db.Update<DownloadTask>()
                   .Set(a => a.Status, TaskStatus.Pending)
-                  .Set(a => a.Error, null)
+                  .Set(a => a.Error, "")
                   .Set(a => a.Progress, 0)
                   .Set(a => a.UpdateTime, DateTime.Now)
                   .Where(a => a.Status == TaskStatus.Failed && a.TryCount < maxRetry)
                   .ExecuteAffrows();
+
             }
             catch { }
             _cts = new CancellationTokenSource();
@@ -125,9 +126,9 @@ namespace FATrace.OEMApp.Services
         }
 
         /// <summary>
-        /// 后台主循环：定期拉取最早的 Pending 任务并顺序处理。
+        /// 后台主循环：定期拉取最早的 Pending 任务并顺序处理
         /// </summary>
-        /// <param name="token">取消令牌。</param>
+        /// <param name="token">取消令牌</param>
         private async Task RunAsync(CancellationToken token)
         {
             while (!token.IsCancellationRequested)
@@ -211,8 +212,9 @@ namespace FATrace.OEMApp.Services
                 .ExecuteAffrowsAsync();
 
             // 事件 -> TCS
-            // 订阅两个事件：进度与完成。进度事件写回数据库；完成事件用于唤醒等待。
+            // 订阅两个事件：进度与完成。进度事件写回数据库；完成事件用于唤醒等待
             var tcs = new TaskCompletionSource<bool>(TaskCreationOptions.RunContinuationsAsynchronously);
+            
             void OnProgress(object? s, short p)
             {
                 try