### Preflight Checklist - [x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20state%3Aopen%20label%3Abug) and this hasn't been reported yet - [x] This is a single bug report (please file separate reports for different bugs) - [x] I am using the latest version of Claude Code ### What's Wrong? [BUG] Cowork Windows - sandbox-helper fails to mount host share (virtiofs/Plan9) with OneDr

[BUG] Cowork Windows - sandbox-helper fails to mount host share (virtiofs/Plan9) with OneDrive-synced folders

Resolved 💬 7 comments Opened Feb 12, 2026 by EricSev Closed Feb 13, 2026

Preflight Checklist

[x] I have searched existing issues and this hasn't been reported yet
[x] This is a single bug report (please file separate reports for different bugs)
[x] I am using the latest version of Claude Code

What's Wrong?

<html>
<body>
<html><head></head><body><h1>[BUG] Cowork Windows - sandbox-helper fails to mount host share (virtiofs/Plan9) with OneDrive-synced folders</h1>
<h2>Preflight Checklist</h2>
<ul>
<li>[x] I have searched <a href="https://github.com/anthropics/claude-code/issues?q=is%3Aissue+state%3Aopen+label%3Abug">existing issues</a> and this hasn't been reported yet</li>
<li>[x] This is a single bug report (please file separate reports for different bugs)</li>
<li>[x] I am using the latest version of Claude Code</li>
</ul>
<h2>What's Wrong?</h2>
<p>Cowork fails at VM startup with a sandbox mount error. The workspace never reaches API connection; it crashes during the host-share mounting phase. My working directories are stored on OneDrive, which may be the root cause since OneDrive uses the Windows Cloud Files API (placeholder/dehydrated files) rather than standard NTFS file access.</p>
<p><strong>Error output:</strong></p>
<pre><code>CLI output was not valid JSON. This may indicate an error during startup.
Output: sandbox-helper: failed to unmount host share (tried both virtiofs and Plan9): invalid argument
</code></pre>
<p>The sandbox-helper attempts both virtiofs and Plan 9 (9p) filesystem protocols to mount the shared folder from the Windows host into the Linux VM. Both fail with "invalid argument," suggesting the underlying filesystem (OneDrive's cloud files layer) is incompatible with the host-share mechanism.</p>
<p>Regular Chat mode works without issues. Only Cowork is affected.</p>
<h2>What Should Happen?</h2>
<p>Cowork should either:</p>
<ol>
<li>Successfully mount OneDrive-synced folders via virtiofs or Plan 9, or</li>
<li>Detect OneDrive paths and provide a clear error message guiding the user to select a local (non-OneDrive) working directory</li>
</ol>
<h2>Steps to Reproduce</h2>
<ol>
<li>Have a Windows 11 Home system with OneDrive enabled and documents stored in OneDrive-synced folders</li>
<li>Open Claude Desktop (latest version, Feb 2026)</li>
<li>Switch to Cowork tab</li>
<li>Start any task</li>
<li>Observe: sandbox-helper mount failure before the workspace can start</li>
</ol>
<h2>Suspected Root Cause</h2>
<p>OneDrive's Cloud Files API presents files as placeholder/dehydrated stubs on disk. The virtiofs and Plan 9 host-share protocols likely expect standard NTFS file access and cannot traverse OneDrive's filter driver. The mount call returns EINVAL ("invalid argument") because the filesystem at the shared path isn't a conventional local filesystem.</p>
<p>This may also affect other cloud storage providers that use similar virtual filesystem drivers (e.g., Dropbox Smart Sync, Google Drive streaming).</p>
<h2>Troubleshooting Attempted</h2>
<ul>
<li>Verified Windows Features: Virtual Machine Platform ✅, Windows Hypervisor Platform ✅ (Hyper-V not available on Home edition)</li>
<li>Restarted Claude Desktop multiple times</li>
<li>No VPN active</li>
<li>Windows Defender Firewall: Claude allowed on both Private and Public networks</li>
<li>Have not yet tested with a non-OneDrive local folder (will update if this resolves the issue)</li>
</ul>
<h2>Environment</h2>

<h2>Claude Model</h2>
<p>Opus</p>
<h2>Is this a regression?</h2>
<p>No, this never worked</p>
<h2>Claude Code Version</h2>
<p>Claude Desktop latest version (Windows, downloaded Feb 2026). This is Cowork on Claude Desktop, not Claude Code CLI.</p>
<h2>Platform</h2>
<p>Anthropic API</p>
<h2>Operating System</h2>
<p>Windows</p>
<h2>Additional Context</h2>
<ul>
<li>Windows 11 Home does not include Hyper-V; only Virtual Machine Platform and Windows Hypervisor Platform are available. It is unclear whether Cowork's VM layer requires full Hyper-V.</li>
<li>Possibly related to #24918, #24945, #24962 (other Windows Cowork VM failures), though those report API connectivity issues rather than this specific mount failure.</li>
<li>The "tried both virtiofs and Plan9" message suggests the sandbox-helper has a fallback path, but both protocols fail against the OneDrive filesystem driver.</li>
<li>A potential fix or workaround might involve copying files to a local staging directory before mounting into the VM, rather than sharing the OneDrive path directly.</li>
</ul></body></html>
</body>
</html># [BUG] Cowork Windows - sandbox-helper fails to mount host share (virtiofs/Plan9) with OneDrive-synced folders

Preflight Checklist

[x] I have searched [existing issues](https://github.com/anthropics/claude-code/issues?q=is%3Aissue+state%3Aopen+label%3Abug) and this hasn't been reported yet
[x] This is a single bug report (please file separate reports for different bugs)
[x] I am using the latest version of Claude Code

What's Wrong?

Cowork fails at VM startup with a sandbox mount error. The workspace never reaches API connection; it crashes during the host-share mounting phase. My working directories are stored on OneDrive, which may be the root cause since OneDrive uses the Windows Cloud Files API (placeholder/dehydrated files) rather than standard NTFS file access.

Error output:

CLI output was not valid JSON. This may indicate an error during startup.
Output: sandbox-helper: failed to unmount host share (tried both virtiofs and Plan9): invalid argument

The sandbox-helper attempts both virtiofs and Plan 9 (9p) filesystem protocols to mount the shared folder from the Windows host into the Linux VM. Both fail with "invalid argument," suggesting the underlying filesystem (OneDrive's cloud files layer) is incompatible with the host-share mechanism.

Regular Chat mode works without issues. Only Cowork is affected.

What Should Happen?

Cowork should either:

Successfully mount OneDrive-synced folders via virtiofs or Plan 9, or
Detect OneDrive paths and provide a clear error message guiding the user to select a local (non-OneDrive) working directory

Steps to Reproduce

Have a Windows 11 Home system with OneDrive enabled and documents stored in OneDrive-synced folders
Open Claude Desktop (latest version, Feb 2026)
Switch to Cowork tab
Start any task
Observe: sandbox-helper mount failure before the workspace can start

Suspected Root Cause

OneDrive's Cloud Files API presents files as placeholder/dehydrated stubs on disk. The virtiofs and Plan 9 host-share protocols likely expect standard NTFS file access and cannot traverse OneDrive's filter driver. The mount call returns EINVAL ("invalid argument") because the filesystem at the shared path isn't a conventional local filesystem.

This may also affect other cloud storage providers that use similar virtual filesystem drivers (e.g., Dropbox Smart Sync, Google Drive streaming).

Troubleshooting Attempted

Verified Windows Features: Virtual Machine Platform ✅, Windows Hypervisor Platform ✅ (Hyper-V not available on Home edition)
Restarted Claude Desktop multiple times
No VPN active
Windows Defender Firewall: Claude allowed on both Private and Public networks
Have not yet tested with a non-OneDrive local folder (will update if this resolves the issue)

Environment

| Component | Detail |
|---|---|
| OS | Windows 11 Home, Version 25H2, Build 26200.7840 |
| Processor | 13th Gen Intel Core i7-13700HX (2.10 GHz) |
| RAM | 32 GB |
| System type | 64-bit, x64-based processor |
| Claude Desktop | Latest version (downloaded Feb 2026) |
| OneDrive | Active, documents stored in OneDrive-synced folders |
| Windows Feature Experience Pack | 1000.26100.291.0 |

Claude Model

Opus

Is this a regression?

No, this never worked

Claude Code Version

Claude Desktop latest version (Windows, downloaded Feb 2026). This is Cowork on Claude Desktop, not Claude Code CLI.

Platform

Anthropic API

Operating System

Windows

Additional Context

Windows 11 Home does not include Hyper-V; only Virtual Machine Platform and Windows Hypervisor Platform are available. It is unclear whether Cowork's VM layer requires full Hyper-V.
Possibly related to #24918, #24945, #24962 (other Windows Cowork VM failures), though those report API connectivity issues rather than this specific mount failure.
The "tried both virtiofs and Plan9" message suggests the sandbox-helper has a fallback path, but both protocols fail against the OneDrive filesystem driver.
A potential fix or workaround might involve copying files to a local staging directory before mounting into the VM, rather than sharing the OneDrive path directly.

What Should Happen?

Cowork should access the directory and subdirectories

Error Messages/Logs

CLI output was not valid JSON. This may indicate an error during startup. Output: sandbox-helper: failed to unmount host share (tried both virtiofs and Plan9): invalid argument

Steps to Reproduce

Start Claude Desktop in Windows Home OS
Select directory or folder (on OneDrive)
Enter Prompt and click the go arrow

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Cowork

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_

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