[feat] add in-app updates for desktop installations

apps/desktop/src/updater/update_controller.h

@@ -0,0 +1,43 @@
+/*
+ * @Author: DI JUNKUN
+ * @Date: 2026-10-20
+ * Copyright (c) 2026 by DI JUNKUN, All Rights Reserved.
+ */
+
+#ifndef _UPDATE_CONTROLLER_H_
+#define _UPDATE_CONTROLLER_H_
+
+#include "updater/update_core.h"
+#include <future>
+
+namespace crossdesk::updater {
+class Controller {
+ public:
+  enum class State { Idle, Downloading, Preparing, Ready, Failed };
+  explicit Controller(fs::path cache);
+  ~Controller();
+  bool Available(const std::string& envelope) const;
+  void Start(const std::string& envelope);
+  // Returns true only after a live helper has acknowledged the prepared job.
+  bool Poll();
+  void Cancel();
+  void ConfirmStartup();
+  State state() const { return state_; }
+  int progress() const { return progress_.load(); }
+  const std::string& error() const { return error_; }
+  bool busy() const { return state_ == State::Downloading || state_ == State::Preparing; }
+ private:
+  fs::path cache_, job_;
+  State state_ = State::Idle;
+  std::string error_;
+  mutable std::string checked_envelope_;
+  mutable bool checked_ = false;
+  mutable bool available_ = false;
+  std::atomic<int> progress_{0};
+  std::atomic<bool> cancel_{false};
+  std::future<fs::path> pending_;
+  std::chrono::steady_clock::time_point deadline_{};
+};
+}  // namespace crossdesk::updater
+
+#endif