Module gui::gui_headless

GUI: the headless backend.

A complete struct GuiBackend (gui_backend.h) that keeps windows in memory only: nothing is shown, presenting just counts frames, the clipboard is a process-local string, and the clock is virtual — it moves only when gui_headless_advance() moves it (or when an event loop waits: a pump with a timeout and nothing queued advances the clock by that timeout instead of sleeping). That makes everything above the backend — multi-window event routing, timers, animation frames, the widget toolkit — testable deterministically, on any target, with no display server; it's also how to render GUI frames on a server.

gui_use_headless();                     // before the first window
struct GuiWindow win = GuiWindow::create("t", 200, 100);
gui_headless_click(&win, 10.0, 10.0);   // MOUSE_DOWN + MOUSE_UP
gui_headless_type(&win, "héllo");        // KEY_DOWN/UP per character
while (win.poll_event(&ev)) { ... }

Events injected for a window arrive through that window's poll_event() (or GuiApp's loop) exactly as a platform backend's would, with windowId, timeMs and double-click counts filled in. Window operations behave like a cooperative window manager: set_size() posts GUI_EVENT_RESIZE, set_position() GUI_EVENT_MOVE, focus() FOCUS_OUT to the old focus window and FOCUS_IN to the new one, request_close() GUI_EVENT_CLOSE.