Add configurable service proxy (#1280)

* Add configurable service proxy

* Fix service proxy URL used when opening scripts with a public base URL

When a public proxy URL was configured, the View link was falling through
to direct connection logic and opening the wrong URL. Move the public URL
early-return before connection-type checks, and remove the now-dead
duplicate check further down.

* Add service proxy documentation

Covers config options, URL generation format, wildcard DNS setup,
and reverse proxy Host header requirements.

* Cap combined public service label and document hostname format

* Address service proxy review feedback

packages/server/src/utils/script-hostname.ts

@@ -1,15 +1,48 @@
 import { slugify } from "./worktree.js";
 
+const MAX_DNS_LABEL_LENGTH = 63;
+
 interface BuildScriptHostnameOptions {
   projectSlug: string;
   branchName: string | null;
   scriptName: string;
 }
 
+interface BuildPublicScriptHostnameOptions extends BuildScriptHostnameOptions {
+  publicBaseUrl: string;
+}
+
 function toHostnameLabel(value: string): string {
   return slugify(value) || "untitled";
 }
 
+function capDnsLabel(label: string): string {
+  if (label.length <= MAX_DNS_LABEL_LENGTH) {
+    return label;
+  }
+  return label.slice(0, MAX_DNS_LABEL_LENGTH).replace(/-+$/g, "") || "untitled";
+}
+
+function toPublicServiceLabel({
+  projectSlug,
+  branchName,
+  scriptName,
+}: BuildScriptHostnameOptions): string {
+  const labels = [toHostnameLabel(scriptName)];
+  const isDefaultBranch = branchName === null || branchName === "main" || branchName === "master";
+  if (!isDefaultBranch) {
+    labels.push(toHostnameLabel(branchName));
+  }
+  labels.push(toHostnameLabel(projectSlug));
+
+  // Public URLs must keep script/branch/project in one label. The local
+  // script.branch.project.localhost shape would require multi-level wildcard
+  // DNS/certificates for arbitrary branch names, while a single label works with
+  // normal `*.base-domain` DNS and wildcard TLS. Cap it to the DNS 63-octet
+  // label limit so long branch/project/script names still produce resolvable URLs.
+  return capDnsLabel(labels.join("--"));
+}
+
 export function buildScriptHostname({
   projectSlug,
   branchName,
@@ -25,3 +58,18 @@ export function buildScriptHostname({
 
   return `${serviceHostnameLabel}.${toHostnameLabel(branchName)}.${projectHostnameLabel}.localhost`;
 }
+
+export function buildPublicScriptHostname({
+  publicBaseUrl,
+  ...script
+}: BuildPublicScriptHostnameOptions): string {
+  const base = new URL(publicBaseUrl);
+  return `${toPublicServiceLabel(script)}.${base.hostname}`;
+}
+
+export function buildPublicScriptProxyUrl(options: BuildPublicScriptHostnameOptions): string {
+  const base = new URL(options.publicBaseUrl);
+  const hostname = buildPublicScriptHostname(options);
+  const port = base.port ? `:${base.port}` : "";
+  return `${base.protocol}//${hostname}${port}`;
+}