refactor(xsnap): Remove redundant defer.js (#9745)

This removes some stale code from before embracing makePromiseKit()

packages/xsnap/src/xsnap.js

@@ -10,18 +10,14 @@ import { makeNodeReader, makeNodeWriter } from '@endo/stream-node';
 import { makePromiseKit, racePromises } from '@endo/promise-kit';
 import { forever } from '@agoric/internal';
 import { ErrorCode, ErrorSignal, ErrorMessage, METER_TYPE } from '../api.js';
-import { defer } from './defer.js';
+
+/** @import {PromiseKit} from '@endo/promise-kit' */
 
 /**
  * @typedef {typeof import('child_process').spawn} Spawn
  * @import {Writable} from 'stream'
  */
 
-/**
- * @template T
- * @typedef {import('./defer.js').Deferred<T>} Deferred
- */
-
 // This will need adjustment, but seems to be fine for a start.
 export const DEFAULT_CRANK_METERING_LIMIT = 1e8;
 
@@ -185,8 +181,8 @@ export async function xsnap(options) {
     import.meta.url,
   ).pathname;
 
-  /** @type {Deferred<void>} */
-  const vatExit = defer();
+  /** @type {PromiseKit<void>} */
+  const vatExit = makePromiseKit();
 
   assert(!/^-/.test(name), `name '${name}' cannot start with hyphen`);
 

packages/xsnap/src/xsrepl.js

@@ -4,17 +4,15 @@
 
 import '@endo/init';
 
-/**
- * @template T
- * @typedef {import('./defer.js').Deferred<T>} Deferred
- */
 import * as childProcess from 'child_process';
 import fs from 'fs';
 import { tmpName } from 'tmp';
 import * as os from 'os';
 import * as readline from 'readline';
+import { makePromiseKit } from '@endo/promise-kit';
 import { xsnap } from './xsnap.js';
-import { defer } from './defer.js';
+
+/** @import {PromiseKit} from '@endo/promise-kit' */
 
 const decoder = new TextDecoder();
 
@@ -65,7 +63,9 @@ async function main() {
    * @returns {Promise<string>}
    */
   function ask(prompt) {
-    const { promise, resolve } = /** @type {Deferred<string>} */ (defer());
+    const { promise, resolve } = /** @type {PromiseKit<string>} */ (
+      makePromiseKit()
+    );
     rl.question(prompt, resolve);
     return promise;
   }