fix: check if sandbox-exec is available (#696)

- Introduce `isSandboxExecAvailable()` helper and tidy import ordering
in `handle-exec-command.ts`.
- Add runtime check for the `sandbox-exec` binary on macOS; fall back to
`SandboxType.NONE` with a warning if it’s missing, preventing crashes.

---------

Signed-off-by: Thibault Sottiaux <tibo@openai.com>
Co-authored-by: Fouad Matin <fouad@openai.com>

codex-cli/src/utils/config.ts

@@ -65,6 +65,10 @@ export let OPENAI_API_KEY = process.env["OPENAI_API_KEY"] || "";
 export const OPENAI_ORGANIZATION = process.env["OPENAI_ORGANIZATION"] || "";
 export const OPENAI_PROJECT = process.env["OPENAI_PROJECT"] || "";
 
+export const CODEX_UNSAFE_ALLOW_NO_SANDBOX = Boolean(
+  process.env["CODEX_UNSAFE_ALLOW_NO_SANDBOX"] || "",
+);
+
 export function setApiKey(apiKey: string): void {
   OPENAI_API_KEY = apiKey;
 }