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/test/vat.test.js

@@ -167,9 +167,14 @@ test("a vat granted a host reaches it through the switchboard: fetch and WebSock
 	assert.equal(await probe("erin", echo.host, true), "echo: hello\n");
 });
 
-test("same code, no grant: no fetch", async () => {
+test("same code, no grant: no egress", async () => {
 	await admin.install("frank", await app("egress-probe.js"));
-	assert.match(await probe("frank", echo.host), /^refused: This worker is not permitted to access the internet/);
+	assert.equal(await probe("frank", echo.host), "no egress granted\n");
+});
+
+test("a grant is an object, not ambient: the global fetch still throws", async () => {
+	await admin.install("heidi", await app("try-fetch.js"), echo.host);
+	assert.match(await pub.get("heidi"), /^fetch refused: This worker is not permitted to access the internet/);
 });
 
 test("a grant covers one host only", async () => {