[BUG] CoWork: Edit tool silently hangs on /mnt/.claude/ (read-only mount) — no error, turn produces no output

Description

When a CoWork session attempts to use the sandbox Edit tool on any file under /mnt/.claude/ (the mounted .claude directory), the tool call silently hangs. No error is returned, no output is produced, and the entire turn dies. The user sees nothing — it appears as if Claude went unresponsive.

Steps to Reproduce

1. Open a CoWork session in Claude Desktop on Windows
2. Ask Claude to edit CLAUDE.md (which lives at /sessions/<name>/mnt/.claude/CLAUDE.md inside the sandbox)
3. Claude reads the file successfully (Read tool works fine)
4. Claude calls the Edit tool to modify the file
5. The turn silently dies — no error message, no output, no indication of failure

Expected Behavior

The Edit tool should return an error like Permission denied: /mnt/.claude/ is mounted read-only so the assistant can report the failure and use an alternative approach.

Actual Behavior

The Edit tool call never returns. The assistant's turn ends with zero output. From the user's perspective, Claude appears "stuck" or "brain-dead." This happened 4+ times in a single session, requiring the user to manually intervene each time.

Impact

This is particularly damaging because:

• The assistant doesn't know it failed (no error to catch)
• The user sees no output and has to guess what went wrong
• The assistant will retry the same failing approach unless explicitly told to stop
• It trains users to distrust CoWork's reliability

Environment

• Claude Desktop v1.1617.0 (Windows, MSIX)
• CoWork VM bundle version: 5680b11bcdab215cccf07e0c0bd1bd9213b0c25d
• claude-code-vm SDK: 2.1.92
• Windows 11 Pro

Workaround

Use the Anthropic Filesystem extension or Desktop Commander's start_process to write to the Windows-side .claude/CLAUDE.md path instead of the sandbox mount. Document the restriction in CLAUDE.md so the assistant avoids calling Edit on /mnt/.claude/ paths.

Related Issues

• #25663 (sandbox mount point issues)
• #27649 (silent freeze on complex tasks — similar symptom, different root cause)