fix(xsnap): incorporate PR review suggestions

packages/xsnap/test/fixture-xsnap-eof.js

@@ -0,0 +1,24 @@
+import console from 'console';
+import * as proc from 'child_process';
+import * as os from 'os';
+import fs from 'fs';
+import process from 'node:process';
+import { tmpName } from 'tmp';
+import '@endo/init';
+import { xsnap } from '../src/xsnap.js';
+import { options } from './message-tools.js';
+
+const io = { spawn: proc.spawn, os: os.type(), fs, tmpName };
+
+async function handleCommand(_message) {
+  process.kill(process.pid, 'SIGKILL');
+  return new Uint8Array();
+}
+
+const vat = await xsnap({ ...options(io), handleCommand });
+await vat.evaluate(
+  'function handleCommand(message) { issueCommand(new Uint8Array().buffer); };',
+);
+await vat.issueStringCommand('0');
+console.error('Error: parent was not killed!');
+await vat.close();