Function wait_for_browser_hwnd 

fn wait_for_browser_hwnd(
    state: &Arc<AppState>,
    label: &str,
    timeout: Duration,
) -> Option<*mut c_void>

Poll state.browsers for label until its host’s HWND is non-null or the deadline elapses. Returns the HWND as a raw pointer. Releases the browsers mutex between polls so on_after_created can register on the UI thread.