Function ensure_installed_with 

pub async fn ensure_installed_with<F>(
    paths: DataPaths,
    req: NpmInstallRequest,
    wait: Duration,
    install: F,
) -> Result<PathBuf, EnsureError>
where
    F: FnOnce(&DataPaths, &NpmInstallRequest) -> Result<InstallOutcome, InstallError> + Send + 'static,

The pinned CLI for a provider whose install is missing: install it, waiting up to wait. install is injected so tests don’t need npm.

This is what the UI’s launch flow does on a pin bump (ResolveCli installs and waits). agent.open used to refuse instead, with CLI_NOT_AVAILABLE, for the minute or two after an upgrade while the new pin downloaded.