[fix] prevent remote input from blocking transport callbacks

apps/desktop/src/platform/windows/gui/application/unattended_application.cpp

@@ -64,6 +64,7 @@ int GuiApplication::RunUnattended(void* stop_event) {
   }
 
   // Quiesce network callbacks before destroying the controllers they use.
+  remote_input_.Stop();
   CloseAllRemoteSessions();
   WaitForSessionCleanup();
   keyboard_.ReleaseAllRemotePressedKeys("unattended_host_exit");

apps/desktop/src/platform/windows/input/windows_input_injector.cpp

@@ -16,6 +16,7 @@ namespace {
 struct InputResult {
   UINT sent;
   DWORD error;
+  bool requires_worker = false;
 };
 
 InputResult InjectOnUserDesktop(INPUT* inputs, UINT count) {
@@ -25,7 +26,10 @@ InputResult InjectOnUserDesktop(INPUT* inputs, UINT count) {
   ScopedInteractiveDesktop desktop;
   if (!desktop.Bind(L"")) {
     const DWORD error = GetLastError();
-    return {0, error != ERROR_SUCCESS ? error : ERROR_GEN_FAILURE};
+    // A library may have created a window/hook on an opted-in thread. This
+    // failure occurs before SendInput, so retrying on the worker is safe.
+    return {0, error != ERROR_SUCCESS ? error : ERROR_GEN_FAILURE,
+            error == ERROR_BUSY};
   }
   if (!desktop.IsReceivingInput()) {
     return {0, ERROR_REQUIRES_INTERACTIVE_WINDOWSTATION};
@@ -99,8 +103,13 @@ UINT SendInputOnUserDesktop(INPUT* inputs, UINT count) {
     SetLastError(ERROR_INVALID_PARAMETER);
     return 0;
   }
-  static UserDesktopInputWorker worker;
-  const InputResult result = worker.Send(inputs, count);
+  InputResult result{0, ERROR_SUCCESS, true};
+  if (ScopedUserDesktopInputThread::IsCurrent())
+    result = InjectOnUserDesktop(inputs, count);
+  if (result.requires_worker) {
+    static UserDesktopInputWorker worker;
+    result = worker.Send(inputs, count);
+  }
   const DWORD error = result.error;
   if (error != ERROR_SUCCESS) {
     // Include session identity even when Windows reports no useful SendInput

apps/desktop/src/platform/windows/input/windows_input_injector.h

@@ -11,9 +11,23 @@
 
 namespace crossdesk {
 
-// Executes on a worker without windows or hooks, attached to this process's
-// current user input desktop. Returns a SendInput count and preserves the
-// worker's failure code in the calling thread's last-error value.
+// Opt in only on the remote input worker. UI/hook callers keep using the
+// fallback worker. Desktop attachment is still checked for each injection.
+class ScopedUserDesktopInputThread {
+ public:
+  ScopedUserDesktopInputThread() { ++depth_; }
+  ~ScopedUserDesktopInputThread() { --depth_; }
+  ScopedUserDesktopInputThread(const ScopedUserDesktopInputThread&) = delete;
+  ScopedUserDesktopInputThread& operator=(const ScopedUserDesktopInputThread&) =
+      delete;
+  static bool IsCurrent() { return depth_ != 0; }
+ private:
+  inline static thread_local unsigned depth_ = 0;
+};
+
+// Executes directly on an opted-in worker, or on the fallback input worker,
+// attached to this process's current user input desktop. Returns a SendInput
+// count and preserves the failure code in the calling thread's last-error value.
 UINT SendInputOnUserDesktop(const INPUT& input);
 
 // Synchronously injects one ordered batch. The caller owns the buffer until