fix: reject UI operations when the input desktop is unavailable

src/WxAgent.Windows/WechatChatClient.cs

@@ -369,6 +369,7 @@ public static partial class WechatChatClient
         }
 
         WechatOperationPolicy.ValidateNames([session], nameof(session));
+        WechatDesktop.EnsureInputAvailable();
         var checkpoint = await ListenerCheckpointStore.LoadAsync(checkpointPath, cancellationToken);
         if (checkpoint is not null && !string.Equals(checkpoint.Session, session, StringComparison.Ordinal))
         {
@@ -548,6 +549,7 @@ public static partial class WechatChatClient
     private static AutomationElement AttachWindow(UIA3Automation automation, CancellationToken cancellationToken)
     {
         cancellationToken.ThrowIfCancellationRequested();
+        WechatDesktop.EnsureInputAvailable();
         var window = WechatDoctor.FindWechatWindow(automation);
         if (window is null || FindByAutomationId(window, WechatLocators.MainView) is null)
         {
@@ -814,6 +816,7 @@ public static partial class WechatChatClient
 
     private static void ClickCenter(AutomationElement element)
     {
+        WechatDesktop.EnsureInputAvailable();
         var bounds = element.BoundingRectangle;
         if (bounds.Width <= 0 || bounds.Height <= 0)
         {
@@ -825,6 +828,7 @@ public static partial class WechatChatClient
 
     private static void ExecuteInputStep(string step, Action action)
     {
+        WechatDesktop.EnsureInputAvailable();
         try
         {
             action();