capsite/toybox: ingress is a capability; a hello-world web vat

E(vatAdmin).makeIngress(labels) reserves a mount and returns an ingress;
whoever holds it serves requests carrying those labels by calling
E(ingress).serve(handler). A vat gets one in its params, like any other
remote object; nothing in a vat's module is an entrypoint. A request
reaches the handler as passable data (method, path, labels, body), and
the response comes back as data (status, headers, body). The handler is
a live reference for now: after a restart its mount answers 503.

vats/hello.js serves hello, world; pnpm hello creates it on a running
toybox (client.js is the Node OCapN client, shared with the tests).

pnpm start and pnpm switchboard never ran: systemd-socket-activate wants
absolute paths for unix sockets.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

toybox/client.js

@@ -0,0 +1,33 @@
+/**
+ * @file An OCapN client for the admin socket, from Node: it registers its
+ * own gateway with the router there and reaches every other peer through
+ * it. Run under SES (see test/lockdown.js).
+ */
+import { makeClient, swissnumFromBytes } from "@endo/ocapn";
+import { newWebSocketRpcSession } from "capnweb";
+import WebSocket from "ws";
+import { locationOf, makeRpcNetLayer } from "./netlayer.js";
+
+/**
+ * An OCapN client on the admin socket: registers its own gateway with the
+ * router there, and reaches every other peer through it.
+ *
+ * @param {string} adminSock
+ * @param {string} designator
+ * @param {{ verbose?: boolean }} [opts] OCapN logging
+ */
+export const connectClient = async (adminSock, designator, { verbose = false } = {}) => {
+	const ws = new WebSocket(`ws+unix:${adminSock}:/`);
+	await new Promise((resolve, reject) => (ws.once("open", resolve), ws.once("error", reject)));
+	const session = newWebSocketRpcSession(ws);
+	const ocapn = makeClient({ debugLabel: designator, verbose });
+	const netlayer = await ocapn.registerNetlayer(
+		makeRpcNetLayer({ designator, openGateway: (d) => session.gateway(d) }),
+	);
+	await session.register(designator, netlayer.gateway);
+	const vatAdmin = await ocapn.enlivenSturdyRef(
+		ocapn.makeSturdyRef(locationOf("vatAdmin"), swissnumFromBytes(new TextEncoder().encode("vatAdmin"))),
+	);
+	return { vatAdmin, close: () => (ocapn.shutdown(), ws.close()) };
+};
+