use spawn instead of exec to avoid injection vulnerability (#416)

https://github.com/openai/codex/pull/160 introduced a call to `exec()`
that takes a format string as an argument, but it is not clear that the
expansions within the format string are escaped safely. As written, it
is possible a carefully crafted command (e.g., if `cwd` were `"; && rm
-rf` or something...) could run arbitrary code.

Moving to `spawn()` makes this a bit better, as now at least `spawn()`
itself won't run an arbitrary process, though I suppose `osascript`
itself still could if the value passed to `-e` were abused. I'm not
clear on the escaping rules for AppleScript to ensure that `safePreview`
and `cwd` are injected safely.

---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/416).
* #423
* #420
* #419
* __->__ #416

codex-cli/src/components/chat/terminal-chat.tsx

@@ -32,7 +32,7 @@ import HelpOverlay from "../help-overlay.js";
 import HistoryOverlay from "../history-overlay.js";
 import ModelOverlay from "../model-overlay.js";
 import { Box, Text } from "ink";
-import { exec } from "node:child_process";
+import { spawn } from "node:child_process";
 import OpenAI from "openai";
 import React, { useEffect, useMemo, useRef, useState } from "react";
 import { inspect } from "util";
@@ -374,9 +374,10 @@ export default function TerminalChat({
           const safePreview = preview.replace(/"/g, '\\"');
           const title = "Codex CLI";
           const cwd = PWD;
-          exec(
-            `osascript -e 'display notification "${safePreview}" with title "${title}" subtitle "${cwd}" sound name "Ping"'`,
-          );
+          spawn("osascript", [
+            "-e",
+            `display notification "${safePreview}" with title "${title}" subtitle "${cwd}" sound name "Ping"`,
+          ]);
         }
       }
     }