[fix] move connection cleanup off the UI thread

apps/desktop/src/gui/runtime/session_lifecycle.cpp

@@ -0,0 +1,47 @@
+#include "runtime/session_lifecycle.h"
+
+namespace crossdesk::gui_detail {
+
+CallbackGuard::CallbackGuard(SessionCallbackGate& callbacks)
+    : callbacks_(callbacks), accepted_(callbacks.BeginCallback()) {}
+
+CallbackGuard::~CallbackGuard() {
+  if (accepted_) {
+    callbacks_.EndCallback();
+  }
+}
+
+bool SessionCallbackGate::IsActive() const {
+  std::lock_guard lock(mutex_);
+  return accepting_callbacks_;
+}
+
+CallbackGuard SessionCallbackGate::Enter() {
+  return CallbackGuard(*this);
+}
+
+bool SessionCallbackGate::BeginCallback() {
+  std::lock_guard lock(mutex_);
+  if (!accepting_callbacks_) {
+    return false;
+  }
+  ++running_callbacks_;
+  return true;
+}
+
+void SessionCallbackGate::EndCallback() {
+  std::lock_guard lock(mutex_);
+  --running_callbacks_;
+  if (running_callbacks_ == 0) {
+    callbacks_finished_.notify_all();
+  }
+}
+
+void SessionCallbackGate::Close() {
+  std::unique_lock lock(mutex_);
+  accepting_callbacks_ = false;
+  // Waiting releases the lock so running callbacks can call EndCallback().
+  callbacks_finished_.wait(lock, [this] { return running_callbacks_ == 0; });
+}
+
+}  // namespace crossdesk::gui_detail