Windows app: Agent sandbox setup (windowsSandbox/setupStart) permanently fails and blocks all conversations on non-ASCII (Hangul) username — works on ASCII profile

What version of the Codex App are you using?

26.623.13972.0 (MSIX Store package OpenAI.Codex_..._x64)

What subscription do you have?

Paid ChatGPT plan (Codex-enabled).

What platform is your computer?

Microsoft Windows NT 10.0.19045.0 x64 (Windows 10 Pro 22H2, build 19045.6466)

What issue are you seeing?

The app launches and stays open, but starting any conversation is permanently blocked by this banner (Korean UI):

관리자 권한으로 Agent 샌드박스를 설정할 수 없습니다 / 계속하려면 업데이트를 다시 시도하세요 (EN: "Cannot set up the Agent sandbox with administrator privileges / Retry the update to continue")

Clicking Retry setup just re-fires windowsSandbox/setupStart and fails again — no UAC prompt, no progress, no error detail shown. The app is 100% unusable: no conversation can be started in any project.

Note this is different from the many existing "app crashes/exits on launch with non-ASCII username" reports (e.g. #28061, #13553, #28079, #27506): here the app runs fine and only the Agent sandbox setup step fails.

What steps can reproduce the bug?

1. Use a Windows account whose profile path contains non-ASCII (Hangul/Korean) characters, e.g. C:\Users\<Hangul-username>.
2. Launch the Codex desktop app and try to start a conversation.
3. → Banner: "관리자 권한으로 Agent 샌드박스를 설정할 수 없습니다…". Retry loops forever.

Isolation / root cause (confirmed):

• On the same machine, a second Windows profile with an ASCII-only username launches Codex and starts conversations without any error.
• Desktop logs are flooded (thousands of lines) with the profile path in mojibaked form, confirming non-ASCII path mishandling (ANSI/CP949 bytes decoded as UTF-8):

``
warning [electron-message-handler] worker_rpc_response_error errorMessage="EPERM: operation not permitted, mkdir 'C:\Users\<garbled>'" ... workerId=git method=review-summary
error [electron-message-handler] [desktop-notifications][unhandled-rejection] Error: EPERM: operation not permitted, mkdir 'C:\Users\<garbled>'
`
<garbled> is the corrupted rendering of the real Hangul username. The windowsSandbox/setupStart` handler almost certainly hits the same path-decoding bug when it tries to create its sandbox working directory.

So: non-ASCII (Hangul) Windows username → sandbox setup cannot create its working dir → setup fails → all chats blocked. This looks like the same root cause behind the sandbox-setup cluster (#29427, #23587, #30445, #29771) for affected users, but pinned to the username/path-encoding trigger.

What is the expected behavior?

The Agent sandbox setup should handle non-ASCII (CJK/Hangul) user profile paths correctly and complete successfully — or degrade gracefully instead of hard-blocking conversation start. The ASCII-profile behavior (works fine) is the expected behavior.

Additional information

Things already tried that did not fix it:

1. Reboot — no change.
2. Enabled Windows "Beta: Use Unicode UTF-8 for worldwide language support" (system ACP/OEMCP/MACCP → 65001; verified chcp = 65001 and %USERPROFILE% resolves correctly). OS-level mojibake gone, but sandbox setup still fails.
3. Full uninstall + reinstall of the app (same latest version) — still fails identically.

The only known workaround is to run Codex under a Windows account with an ASCII-only username.

Requests:

1. Fix non-ASCII/Hangul profile-path handling in the Windows Agent sandbox setup (codex-windows-sandbox-setup.exe / windowsSandbox/setupStart).
2. Surface the actual sandbox-setup failure reason in a user-accessible log (currently only the RPC routing is logged; the real error is invisible).
3. Provide a supported way to run without the local Agent sandbox (e.g. honor sandbox_mode = "danger-full-access" in the desktop app) as a fallback.