[BUG] Tailscale via Homebrew CLI + Mac App Store GUI, both Macs on macOS, Cowork blocked by VPN detector despite Tailscale being a mesh VPN with no traffic interception

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?

Tailscale via Homebrew CLI + Mac App Store GUI, both Macs on macOS, Cowork blocked by VPN detector despite Tailscale being a mesh VPN with no traffic interception

What Should Happen?

Claude Cowork should function without impairment due to Tailscale's VPN.

Error Messages/Logs

Failed to start Claude's workspace
Your network traffic may be routing through a VPN, which can interfere with Claude's workspace. Try disconnecting from your VPN and restarting Claude, or contact your IT administrator for assistance.
Restarting Claude or your computer sometimes resolves this. If it persists, you can reinstall the workspace.

Steps to Reproduce

1. Launch Claude Cowork (App) on a 2020 MacBook Air running macOS 15.7.7.
2. Install Tailscale on a 2017 iMac running macOS 13.7.8.
3. Install Tailscale on a 2020 MacBook Air running macOS 15.7.7.
4. Configure both Tailscale instances to connect to the other (note: Tailscale uses 100.x.x.x IP addresses).
5. Connect both machines via Tailscale.
6. From the iMac, view the MacBook Air's desktop.
7. From the iMac, via the MacBook Air's desktop, attempt to invoke Claude Cowork (App)...the attached error message will be displayed.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude for Mac (App) 1.9255.2 (1dc8f7)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_