[Cowork] MSIX: Write/Glob succeed but Read fails on session dirs until folder mounted

What's Wrong?

On Windows with MSIX installation (AppContainer sandbox), Cowork's file tools (Write/Glob/Read/VM Bash) see different file system views due to MSIX path virtualization:

1. Read cannot read files written by Write on session internal directories (outputs/, uploads/) unless a folder is explicitly approved/mounted
2. VM Bash cannot see files written by Write/Glob — and vice versa
3. Write/Glob succeed, but Read refuses the same path with "outside this session's connected folders"

Steps to Reproduce

1. Install Claude Desktop via MSIX on Windows
2. Open Cowork mode
3. Use Write to create a file in outputs/test.txt — succeeds
4. Use Glob to find it with outputs/**/* — finds the file
5. Use Read to read outputs/test.txt — fails with "outside this session's connected folders"
6. Use VM Bash cat /mnt/outputs/test.txt — file not found (empty directory)
7. Upload a file to the chat — Glob finds it in uploads/, but Read also fails
8. Use request_cowork_directory to mount the MSIX physical path — Read starts working

Root Cause

MSIX AppContainer virtualizes the file system. Cowork tools "think" they're operating at:

C:\Users\...\AppData\Local\Claude-3p\...

But actual I/O is redirected to the MSIX sandbox:

...\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Local\Claude-3p\...

Three tool categories behave differently:

| Tool | Path View | Behavior |
|---|---|---|
| Write / Glob / Edit | MSIX virtualized | Work fine, transparently redirected |
| Read | Requires explicit mount | Rejects session-internal directories until user approves a folder |
| VM Bash (virtiofs) | Real physical paths | Cannot see files written via virtualized paths |

Workaround

Mount the MSIX physical path via request_cowork_directory:

C:\Users\Administrator\AppData\Local\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Local\Claude-3p

After approval, Read works for all session directories under that path.

Environment

• Claude Desktop: MSIX v1.9659.2 (AppContainer sandbox)
• OS: Windows (Hyper-V)
• Mode: Cowork (Research Preview)
• Date: 2026-06-01