__dialog_created(*dlg, type, *_params)
{
    initiateMediaProxyUsage(dlg, _params->msg);
}

initiateMediaProxyUsage(msg, dlg)
{
    if (mediaProxyInitiated) return;
    dlg_api.register_dlgcb...
    use_media_proxy(msg, get_dialog_id(dlg));
    mediaProxyInitiated = true;
}

EngageMediaProxy(msg)
{
    if (dialog_created) {
        dlg = w_get_dlg; # ??
        initiateMediaProxyUsage(msg, dlg);
    }
}