Function post_to_host 

pub(crate) async fn post_to_host(
    http_client: &Client,
    host: &HostIpc,
    route: &str,
    body: Value,
    timeout: Option<Duration>,
) -> Result<Value, String>

ui_handlers::proxy_to_host_timeout for a caller that holds the HTTP client rather than the whole AppState (Tower’s sampler, app_api/tower_pane.rs).