Function handle_ui_browser_navigate 

pub(crate) async fn handle_ui_browser_navigate(
    __arg0: State<AppState>,
    caller: Option<Extension<Caller>>,
    __arg2: Json<UiBrowserNavigateRequest>,
) -> impl IntoResponse

POST /api/v1/ui/browser/navigate — backs BrowserNavigate. Own pane only, and only when it’s a dedicated browser pane (checked host-side).