[BUG] Cowork sandbox: sessiondata.vhdx never created (Intel, virtualization OK)

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?

Environment

Claude Desktop 1.24012.1.0
Windows 11, Intel x64

Error

failed to set session disk path: session disk not found:
...\vm_bundles\claudevm.bundle\sessiondata.vhdx

Everything on the machine checks out

BIOS virtualization (Intel VT-x): enabled (Task Manager → CPU → Virtualization: Enabled)
Windows features: Virtual Machine Platform + Windows Hypervisor Platform + WSL all enabled
bcdedit → hypervisorlaunchtype = Auto
Disk space: 295 GB free on C:

What I tried

Deleted the marker .auto_reinstall_attempted repeatedly — it regenerates every launch, app loops with Skipping auto-reinstall (already attempted once).
Deleted the entire claudevm.bundle folder and let the app fully re-download and rebuild from scratch.
Result: all images provision correctly — rootfs.vhdx (7.5 GB), vmlinuz, initrd, smol-bin — except sessiondata.vhdx, which is never generated.

Key log lines

[VM:start] Auto-reinstalling workspace after startup failure
[deleteVMBundle] Deleting reinstall files from ...\vm_bundles\claudevm.bundle
[deleteVMBundle] Reinstall files deleted (sessiondata.img and compressed cache preserved)
...
[VM:start] Startup failed: Error: failed to set session disk path:
session disk not found: ...\claudevm.bundle\sessiondata.vhdx
[VM:start] Skipping auto-reinstall (already attempted once)

Note: the reinstall claims to preserve sessiondata.img, but neither sessiondata.img nor sessiondata.vhdx ever exists in the bundle — so the session disk is never actually created on a first-run / clean-rebuild machine.

Summary On a clean, correctly-configured Intel machine (virtualization + hypervisor + disk space all fine), the Cowork sandbox never starts because sessiondata.vhdx is never created, and the auto-reinstall path does not fix it. Looks like a build bug in the session-disk creation step, not a host configuration issue.

What Should Happen?

Environment

Claude Desktop 1.24012.1.0
Windows 11, Intel x64

Error

failed to set session disk path: session disk not found:
...\vm_bundles\claudevm.bundle\sessiondata.vhdx

Everything on the machine checks out

BIOS virtualization (Intel VT-x): enabled (Task Manager → CPU → Virtualization: Enabled)
Windows features: Virtual Machine Platform + Windows Hypervisor Platform + WSL all enabled
bcdedit → hypervisorlaunchtype = Auto
Disk space: 295 GB free on C:

What I tried

Deleted the marker .auto_reinstall_attempted repeatedly — it regenerates every launch, app loops with Skipping auto-reinstall (already attempted once).
Deleted the entire claudevm.bundle folder and let the app fully re-download and rebuild from scratch.
Result: all images provision correctly — rootfs.vhdx (7.5 GB), vmlinuz, initrd, smol-bin — except sessiondata.vhdx, which is never generated.

Key log lines

[VM:start] Auto-reinstalling workspace after startup failure
[deleteVMBundle] Deleting reinstall files from ...\vm_bundles\claudevm.bundle
[deleteVMBundle] Reinstall files deleted (sessiondata.img and compressed cache preserved)
...
[VM:start] Startup failed: Error: failed to set session disk path:
session disk not found: ...\claudevm.bundle\sessiondata.vhdx
[VM:start] Skipping auto-reinstall (already attempted once)

Note: the reinstall claims to preserve sessiondata.img, but neither sessiondata.img nor sessiondata.vhdx ever exists in the bundle — so the session disk is never actually created on a first-run / clean-rebuild machine.

Summary On a clean, correctly-configured Intel machine (virtualization + hypervisor + disk space all fine), the Cowork sandbox never starts because sessiondata.vhdx is never created, and the auto-reinstall path does not fix it. Looks like a build bug in the session-disk creation step, not a host configuration issue.

Error Messages/Logs

Steps to Reproduce

Environment

Claude Desktop 1.24012.1.0
Windows 11, Intel x64

Error

failed to set session disk path: session disk not found:
...\vm_bundles\claudevm.bundle\sessiondata.vhdx

Everything on the machine checks out

BIOS virtualization (Intel VT-x): enabled (Task Manager → CPU → Virtualization: Enabled)
Windows features: Virtual Machine Platform + Windows Hypervisor Platform + WSL all enabled
bcdedit → hypervisorlaunchtype = Auto
Disk space: 295 GB free on C:

What I tried

Deleted the marker .auto_reinstall_attempted repeatedly — it regenerates every launch, app loops with Skipping auto-reinstall (already attempted once).
Deleted the entire claudevm.bundle folder and let the app fully re-download and rebuild from scratch.
Result: all images provision correctly — rootfs.vhdx (7.5 GB), vmlinuz, initrd, smol-bin — except sessiondata.vhdx, which is never generated.

Key log lines

[VM:start] Auto-reinstalling workspace after startup failure
[deleteVMBundle] Deleting reinstall files from ...\vm_bundles\claudevm.bundle
[deleteVMBundle] Reinstall files deleted (sessiondata.img and compressed cache preserved)
...
[VM:start] Startup failed: Error: failed to set session disk path:
session disk not found: ...\claudevm.bundle\sessiondata.vhdx
[VM:start] Skipping auto-reinstall (already attempted once)

Note: the reinstall claims to preserve sessiondata.img, but neither sessiondata.img nor sessiondata.vhdx ever exists in the bundle — so the session disk is never actually created on a first-run / clean-rebuild machine.

Summary On a clean, correctly-configured Intel machine (virtualization + hypervisor + disk space all fine), the Cowork sandbox never starts because sessiondata.vhdx is never created, and the auto-reinstall path does not fix it. Looks like a build bug in the session-disk creation step, not a host configuration issue.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.24012.1.0

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_