[BUG] Cowork "Download failed' on macOS Taho 26.4.1 M4

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?

Platform: darwin-arm64 (M4)
macOS: Tahoe 26.4.1
Claude version: 2.1.138

Error: "Failed to start Claude's workspace — Download failed"

Troubleshooting already tried:

• Disabled VPN (Atmos Agent)
• Tested on mobile hotspot
• Confirmed download server reachable (HTTP/2 200)
• Reinstalled via Homebrew (claude-code 2.1.126)
• Reinstalled via curl install.sh (2.1.138)
• Fixed PATH
• Restarted Mac multiple times

claude doctor output:
Diagnostics
├ Currently running: native (2.1.138)
├ Commit: d6d494651eb4
├ Platform: darwin-arm64
├ Path: /Users/ashley.rupekaspreetail.com/.local/share/claude/versions/2.1.138
├ Config install method: native
└ Search: OK (bundled)

Updates
├ Auto-updates: enabled
├ Auto-update channel: latest
├ Stable version: 2.1.126
└ Latest version: 2.1.138

What Should Happen?

Cowork workspace should download and initialize successfully, allowing me to use the Cowork tab in Claude Desktop.

Error Messages/Logs

"Failed to start Claude's workspace — Download failed"

Steps to Reproduce

1. Install Claude Desktop on a Mac with Apple M4 chip running macOS Tahoe 26.4.1
2. Open Claude Desktop and navigate to the Cowork tab
3. Observe workspace setup begins ("Setting up Claude's workspace...")
4. Progress bar reaches 100% then fails with "Failed to start Claude's workspace — Download failed"

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

n/a

Claude Code Version

2.1.138

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

M4 Mac, first-time setup. Troubleshooting already attempted: disabled VPN (Atmos Agent), tested on mobile hotspot, confirmed download server reachable (HTTP/2 200), reinstalled via Homebrew, reinstalled via curl install.sh, restarted multiple times. Error cycles between ERR_QUIC_PROTOCOL_ERROR and Download failed. claude doctor output: darwin-arm64, version 2.1.138, native install.