[Windows] Desktop app installation fails with 0x80073CF6 / windows.stateExtension on build 29648

Summary

The official Codex Windows desktop app cannot be installed. Microsoft Store and direct package registration both fail with 0x80073CF6.

Environment

• OS: Windows 10 Pro, Insider Dev build 29648.1000.amd64fre.rs_prerelease.260807-1623
• Architecture: x64
• Codex package: OpenAI.Codex_26.818.3698.0_x64__2p2nqsd0c76g0
• Installation source: official Microsoft Store / official Codex installer link

Error

The AppX deployment log reports:

• 0x800700B7: creation of the secure system app data folder failed because the file already exists
• windows.stateExtension registration failed with 0x800700B7
• rollback then reports 0x800703FA: registry key is marked for deletion
• final deployment error: 0x80073CF6

The package is downloaded and its signature/SHA-256 were verified. The failure occurs during AppX registration, not download or signature validation.

Steps already tried

• Reset and re-registered Microsoft Store
• DISM /Online /Cleanup-Image /RestoreHealth
• sfc /scannow
• Windows repair/in-place repair installation
• Removed OpenAI.Codex StateRepository records and WindowsApps remnants
• Verified MSIX SHA-256 and Authenticode signature
• Rebooted repeatedly
• Tested installation with a new Windows user account
• Retried Microsoft Store, winget, the official installer link, and Add-AppxPackage -Register

The same registration error remains for a new Windows user, so this does not appear to be limited to one user profile.

Additional observation

The package manifest declares MaxVersionTested="10.0.26100.0", while this machine is on Insider build 29648.

Expected behavior

The official Codex desktop app should install and register successfully on Windows, or report a clear unsupported-build requirement.

Request

Please confirm whether build 29648 is unsupported and whether a newer package or workaround exists for the windows.stateExtension registration failure.