capsite/toybox: a grant is an object in env, not the vat's global fetch

A vat's globalOutbound is now always null. A granted host arrives as
env.egress, an Egress the app can hand to whichever of its parts should
have it; as globalOutbound it was ambient to every module in the vat.

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

toybox/apps/egress-probe.js

@@ -1,13 +1,15 @@
 import { DurableObject } from "cloudflare:workers";
 
-/** `?url=<target>` fetches it; with `&ws=1`, opens a WebSocket there and reports the echo of "hello". */
+/** `?url=<target>` fetches it through `env.egress`; with `&ws=1`, opens a WebSocket there and reports the echo of "hello". */
 export class App extends DurableObject {
 	async fetch(request) {
 		const params = new URL(request.url).searchParams;
 		const target = params.get("url");
+		const { egress } = this.env;
+		if (!egress) return new Response("no egress granted\n");
 		try {
-			if (!params.has("ws")) return new Response(`got: ${await (await fetch(target)).text()}\n`);
-			const resp = await fetch(target, { headers: { Upgrade: "websocket" } });
+			if (!params.has("ws")) return new Response(`got: ${await (await egress.fetch(target)).text()}\n`);
+			const resp = await egress.fetch(target, { headers: { Upgrade: "websocket" } });
 			const ws = resp.webSocket;
 			if (!ws) return new Response(`no websocket: ${resp.status} ${await resp.text()}`);
 			ws.accept();