Function open_floating_pane_window 

pub fn open_floating_pane_window(
    state: &Arc<AppState>,
    args: &Value,
) -> Result<Value, String>

IPC handler — called when the frontend or an agent invokes open_floating_pane_window on the host. Validates input, allocates a stable label, and posts a UI-thread task to create the owned HWND and embed a CEF browser inside it.