when a helm chart deploys a service, how do you then get the hostname/port from the outputs?

Does this example in the docs answer your question? It demonstrates how to access resources deployed via

helm.v3.Chart

. You didn't specify the language you're using, here's the example in TypeScript:

import * as k8s from "@pulumi/kubernetes";

// Deploy the latest version of the bitnami/wordpress chart.
const wordpress = new k8s.helm.v3.Chart("wpdev", {
    fetchOpts: {
        repo: "<https://charts.bitnami.com/bitnami>"
    },
    chart: "wordpress",
});

// Export the public IP for WordPress.
const frontend = wordpress.getResource("v1/Service", "default/wpdev-wordpress");
export const frontendIp = frontend.status.loadBalancer.ingress[0].ip;