[BUG] Cowork: FUSE mount of selected folder does not expose pre-existing files (Windows, non-home-dir path)

Description

When selecting a folder outside the home directory (e.g., C:\allvue\03232026_codex) as the Cowork workspace, the FUSE mount is created and is read-write, but pre-existing files on disk are not visible through the mount. Only files created by Cowork after the mount appear.

Environment

• OS: Windows (exact build unknown)
• Claude Desktop: Latest as of 2026-03-30
• Claude Code (sandbox): v2.1.87
• Path selected: C:\allvue\03232026_codex
• Path mounted at: /sessions/<session-id>/mnt/03232026_codex

Evidence

The folder contains 20+ subdirectories (.codex/skills/, projects, etc.) confirmed via Windows Explorer screenshot. Inside the Cowork sandbox:

$ ls -la /sessions/vigilant-wizardly-cray/mnt/03232026_codex/
total 8
drwx------ 2 vigilant-wizardly-cray vigilant-wizardly-cray 4096 Mar 30 05:56 .
drwxr-xr-x 7 vigilant-wizardly-cray vigilant-wizardly-cray 4096 Mar 30 05:56 ..

Mount is present and correct:

$ cat /proc/mounts | grep 03232026
/mnt/allvue/03232026_codex /sessions/vigilant-wizardly-cray/mnt/03232026_codex fuse rw,nosuid,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other 0 0

Raw source is also empty:

$ ls -la /mnt/allvue/03232026_codex/
total 8
drwxr-xr-x 2 root root 4096 Mar 30 05:56 .
drwxr-xr-x 3 root root 4096 Mar 30 05:56 ..

Files written BY Cowork DO appear and persist. Only pre-existing files from the host filesystem are missing.

Reproduction

1. Have files at a path outside the home directory (e.g., C:\allvue\03232026_codex\.codex\skills\)
2. Start a Cowork session and select that folder
3. Observe the mount is created but ls -la shows empty
4. Write a file via Cowork — it appears correctly
5. Pre-existing files remain invisible

Impact

Blocking. Cowork cannot function as an orchestration layer if it cannot read the existing workspace. This prevents reading project files, skill definitions, configuration, and any pre-existing code.

Related Issues

• #29583 — Cannot use folders outside home directory on Windows (marked COMPLETED but this may be a remaining edge case)
• #24964 — Folder picker rejects folders outside home directory
• #5003 — Hidden files not detected (different root cause — this is not a dotfile visibility issue)