capsite/toybox: OCapN vats; createVat takes remote objects

The admin socket now also speaks OCapN over Cap'n Web: a WebSocket there
reaches the VatAdmin DO, an OCapN peer whose bootstrap (swissnum
vatAdmin) offers createVat(src, params). params may hold remote objects;
the vat's root comes back as one.

Each OCapN vat is its own peer: SES and @endo/ocapn run in its facet
(vat-runtime.js, bundled with esbuild), around the vat's own module,
which exports buildRootObject(vatPowers, params). Passing a client's
object to a vat, or a vat's root to the client, is an OCapN handoff, so
the receiver dials the exporter. Nothing here can dial out, so the
VatAdmin is also the router: a client registers its gateway under a
designator, a vat's designator is its id, and every peer reaches every
other through it. The netlayer is ertp-clerk's, made to work over Workers
RPC stubs and plain promises as well as Cap'n Web.

Not yet: sturdyrefs that survive a restart, an adminNode, and grants
(egress, mount) for OCapN vats. App vats (export class App) still work
beside them.

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

toybox/test/ocapn.test.js

@@ -0,0 +1,68 @@
+/** @file OCapN vats: a client on the admin socket creates a vat and passes it a remote object. */
+import { mkdir, mkdtemp, readFile, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { after, before, test } from "node:test";
+import assert from "node:assert/strict";
+import { E, Far } from "@endo/far";
+import { makeClient, swissnumFromBytes } from "@endo/ocapn";
+import { newWebSocketRpcSession } from "capnweb";
+import WebSocket from "ws";
+import { locationOf, makeRpcNetLayer } from "../netlayer.js";
+import { freePort, here, startWorkerd } from "./workerd.js";
+
+const vatSrc = (name) => readFile(join(here, "vats", name), "utf8");
+
+/**
+ * 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
+ */
+const connectClient = async (adminSock, designator) => {
+	const ws = new WebSocket(`ws+unix:${adminSock}:/`);
+	await new Promise((resolve, reject) => (ws.once("open", resolve), ws.once("error", reject)));
+	const session = newWebSocketRpcSession(ws);
+	const ocapn = makeClient({ debugLabel: designator, verbose: !!process.env.OCAPN_LOG });
+	const netlayer = await ocapn.registerNetlayer(
+		makeRpcNetLayer({ designator, openGateway: (d) => session.gateway(d) }),
+	);
+	await session.register(designator, netlayer.gateway);
+	const vatAdmin = await ocapn.enlivenSturdyRef(
+		ocapn.makeSturdyRef(locationOf("vatAdmin"), swissnumFromBytes(new TextEncoder().encode("vatAdmin"))),
+	);
+	return { vatAdmin, close: () => (ocapn.shutdown(), ws.close()) };
+};
+
+let dir, server, client;
+
+before(async () => {
+	dir = await mkdtemp(join(tmpdir(), "toybox-ocapn-"));
+	await mkdir(join(dir, "state"));
+	const port = await freePort();
+	server = await startWorkerd(
+		"config.capnp",
+		[
+			"-s", `http=127.0.0.1:${port}`, "-s", `admin=unix:${join(dir, "admin.sock")}`,
+			"-d", `state=${join(dir, "state")}`, "-e", `switchboard=unix:${join(dir, "no-switchboard.sock")}`,
+		],
+		{ port, host: "127.0.0.1" },
+		[join(dir, "admin.sock")],
+	);
+	client = await connectClient(join(dir, "admin.sock"), "client-1");
+});
+
+after(async () => {
+	client?.close();
+	await server?.stop();
+	await rm(dir, { recursive: true, force: true });
+});
+
+test("createVat passes a remote object in; the vat's root comes back", async () => {
+	const carol = Far("carol", { greet: (name) => `hi ${name}, from carol` });
+	const { id, root } = await E(client.vatAdmin).createVat(await vatSrc("greeter.js"), { carol });
+	assert.match(id, /^[0-9a-f]{64}$/);
+	assert.equal(await E(root).hello(), "hello from the vat");
+	assert.equal(await E(root).greetVia("vat"), "hi vat, from carol");
+});