Windows sandbox setup marker ACL prevents Codex from starting sandbox after UAC setup

What happened?

After installing/reinstalling Codex for Windows, every normal sandbox command repeatedly triggered UAC and then failed with:

windows sandbox: orchestrator_helper_incomplete: setup helper exited successfully before setup completed

The sandbox setup helper itself appeared to complete successfully, but Codex kept treating setup as incomplete:

sandbox setup required: sandbox setup marker missing or incompatible
codex-windows-sandbox-setup.exe] setup binary completed
read-acl-only mode: applying read ACLs
read ACL run completed

The root cause on this machine appears to be the ACL on:

%USERPROFILE%\.codex\.sandbox\setup_marker.json

The file existed and contained a valid-looking marker, but the normal Codex process could not use it until the current Windows user was explicitly granted access. After granting the current user full control on setup_marker.json, normal sandbox commands started working immediately and no longer triggered UAC.

Environment

Codex Windows package: OpenAI.Codex_26.623.5546.0_x64__2p2nqsd0c76g0
Codex executable path: C:\Program Files\WindowsApps\OpenAI.Codex_26.623.5546.0_x64__2p2nqsd0c76g0\app\resources\codex.exe
PowerShell: 5.1.26100.8737
OS: Windows, build 26100 series

Marker file contents after permission was manually fixed

{
  "version": 5,
  "offline_username": "CodexSandboxOffline",
  "online_username": "CodexSandboxOnline",
  "created_at": "2026-06-28T11:57:37.952492200+00:00",
  "proxy_ports": [],
  "allow_local_binding": false,
  "read_roots": [],
  "write_roots": []
}

Observed behavior

1. Run a normal command from Codex on Windows.
2. UAC prompts for codex-windows-sandbox-setup.exe from the Codex WindowsApps package.
3. User approves UAC.
4. Setup log says the helper completed.
5. Codex still fails with orchestrator_helper_incomplete and continues to report setup_marker.json as missing or incompatible.
6. The cycle repeats on subsequent commands.

Workaround

Granting the current Windows user access to the marker file fixed the issue:

icacls "$env:USERPROFILE\.codex\.sandbox\setup_marker.json" /grant "$env:USERDOMAIN\$env:USERNAME:F"

After that, normal sandbox commands succeeded without additional UAC prompts.

Expected behavior

The Windows sandbox setup helper should create setup_marker.json with ACLs that allow the normal Codex process to read/validate it after UAC-approved setup completes. If the marker exists but is unreadable, Codex should surface a clearer ACL/permission error instead of treating it as missing or incompatible.