[BUG] Claude Desktop (MSIX/Windows): renderer cannot open IndexedDB backing store → blank first screen + re-login on every launch (Squirrel build on same profile works)

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported (closest is #65341, but that is a GPU-rendering cause — see "Distinction" below)
• [x] This is a single bug report
• [x] I am using the latest version

What's Wrong?

After following the in-app "update to use Cowork" prompt (which installed the MSIX package, Claude_1.14271.0.0_x64__pzs8sxrjxfjjc, SignatureKind=Developer), two symptoms appear and persist:

1. First launch → blank screen (window frame only, empty dark content area).
2. Every subsequent launch requires re-login — the session is never persisted across restarts.

Before installing the MSIX build (i.e. on the auto-updating Squirrel desktop app), there were no problems.

Root Cause (observed)

The MSIX renderer fails to open its IndexedDB backing store. %APPDATA%\Claude\logs\claude.ai-web.log shows, on every launch:

• Uncaught (in promise) UnknownError: Internal error opening backing store for indexedDB.open.
• [REACT_QUERY_CLIENT] QueryClient error: ["account_profile"] data is undefined
• No active account context.
• TypeError: Failed to fetch (assets-proxy.anthropic.com / api.anthropic.com)

Critically, %APPDATA%\Claude\IndexedDB is never created on disk — it behaves like an in-memory / off-the-record partition. Session/account tokens that should persist in IndexedDB are lost, so each start is treated as logged-out. The blank screen is the same root cause (the web app cannot read local state to initialize).

What Should Happen?

IndexedDB should persist; login should survive a restart (as it does on the Squirrel build).

Steps to Reproduce

1. Install Claude Desktop MSIX build (via the in-app Cowork update prompt / stub installer).
2. Launch → blank screen.
3. Fully quit, relaunch → login screen.
4. Log in, fully quit, relaunch → login required again.

What was ruled out (clean environment, all still reproduce)

• Full profile storage wipe (IndexedDB / Local Storage / Session Storage / caches moved to backup) — blank screen cleared, but the IndexedDB error + re-login persist.
• Restored package capability SID + ALL APPLICATION PACKAGES ACLs on the profile folder (icacls, inherited).
• chkdsk (no bad sectors), sfc /scannow (no integrity violations).
• Windows Defender Controlled Folder Access off; no third-party AV.
• Network reachable (api / assets-proxy / claude.ai all OK); no proxy/VPN.
• Per-user install Add-AppxPackage blocked by 0x80073D28 (package requires admin install).
• Machine-wide Add-AppxProvisionedPackage reinstall — same symptoms.

→ %APPDATA%\Claude\IndexedDB is still never created. Points to an app/packaging issue, not profile/disk/system.

Workaround / Contrast (key signal)

Reverting to the Squirrel desktop build (%LOCALAPPDATA%\AnthropicClaude, v1.8089.1) → login persists normally on the same profile and network. So this is specific to the MSIX packaging, not GPU.

Distinction from #65341

#65341 is the same blank-screen surface symptom but a GPU rendering cause (driver / RendererCodeIntegrity / GPU cache), fixed with --disable-gpu. This report is a different cause: IndexedDB backing store never opens, and the defining symptom here is re-login on every launch, which GPU flags do not address.

Version

Claude Desktop MSIX v1.14271.0.0 (this is the Desktop app, NOT Claude Code CLI)

Operating System

Windows 11 Home 10.0.26200