[refactor] organize GUI code by responsibility

src/gui/features/clipboard/clipboard_controller.h

@@ -0,0 +1,45 @@
+#ifndef CROSSDESK_GUI_CLIPBOARD_CONTROLLER_H_
+#define CROSSDESK_GUI_CLIPBOARD_CONTROLLER_H_
+
+#include <SDL3/SDL.h>
+
+#include <atomic>
+#include <cstddef>
+#include <cstdint>
+#include <mutex>
+#include <optional>
+#include <string>
+
+namespace crossdesk {
+
+class GuiRuntime;
+
+// Owns clipboard synchronization state and keeps feedback-loop prevention out
+// of the main UI coordinator.
+class ClipboardController {
+public:
+  explicit ClipboardController(GuiRuntime &owner);
+
+  void SetEventType(uint32_t event_type);
+  uint32_t event_type() const;
+
+  void Initialize();
+  void Shutdown();
+  void QueueRemoteText(const char *data, size_t size);
+  void ApplyPendingRemoteText();
+  void HandleLocalUpdate();
+
+private:
+  int SendToPeers(const std::string &text);
+
+  GuiRuntime &owner_;
+  uint32_t event_type_ = 0;
+  std::atomic<bool> events_enabled_{false};
+  std::mutex pending_mutex_;
+  std::optional<std::string> pending_remote_text_;
+  std::string last_text_;
+};
+
+} // namespace crossdesk
+
+#endif // CROSSDESK_GUI_CLIPBOARD_CONTROLLER_H_