[BUG] CoWork sdk_install broken with external drive home directory

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?

CoWork sdk_install broken with external drive home directory — since the April 5 update, the sdk_install VM startup step fails with RPC error: SDK version X not verified at /mnt/.virtiofs-root/shared/Volumes/BotCentral/.... virtiofs does not expose separately-mounted APFS volumes. This step was absent between ~Feb 27 and April 5 (when CoWork worked fine). Regression introduced April 5.

The step being absent for 5+ weeks shows it's not strictly necessary — Anthropic just needs to make it non-blocking for external drive setups, or handle the virtiofs mount correctly.

What Should Happen?

The step being absent for 5+ weeks shows it's not strictly necessary — Anthropic just needs to make it non-blocking for external drive setups, or handle the virtiofs mount correctly.

Error Messages/Logs

Steps to Reproduce

Title: CoWork sessions fail to start when macOS home directory is on an external drive

Steps to reproduce:

1. Set macOS user home directory to an external APFS drive (e.g. /Volumes/BotCentral/Users/milo)
2. Install or update Claude desktop app to version released ~April 5, 2026
3. Open the Claude desktop app → click the Cowork tab
4. Attempt to start a new session — it spins indefinitely on "Starting session..."

Expected: CoWork session starts normally

Actual: Session never starts. ~/Library/Logs/Claude/cowork_vm_node.log shows:

[VM:steps] sdk_install started
[postConnect] Installing SDK: subpath=Volumes/BotCentral/Users/milo/Library/Application Support/Claude/claude-code-vm, version=2.1.87
[VM:start] Startup failed: 'RPC error: SDK version 2.1.87 not verified at /mnt/.virtiofs-root/shared/Volumes/BotCentral/Users/milo/Library/Application Support/Claude/claude-code-vm/2.1.87/.verified'
[VM:start] Skipping auto-reinstall (already attempted once)

Root cause: The CoWork Linux VM accesses the host filesystem via virtiofs (shared at /). Apple's Virtualization Framework virtiofs does not traverse separately-mounted APFS volumes, so /Volumes/BotCentral is invisible inside the VM. The SDK lives on the external drive and cannot be verified.

Additional context:

• This sdk_install step was absent from the app between ~Feb 27 and April 5 — CoWork worked fine during that entire period
• The step never succeeded with an external drive home (failing logs go back to Feb 10)
• The .verified file exists on the host at the correct path with correct permissions — the VM simply cannot see it through virtiofs

Claude Model

Sonnet (default)

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.87 — add that to the bug report as the Claude Code / SDK version.

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_