[BUG] Claude Desktop Cowork — Workspace fails to initialize with ERR_QUIC_PROTOCOL_ERROR (macOS)

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 workspace initialization fails 100% of the time. The progress bar starts, reaches ~13%, then fails with:

net::ERR_QUIC_PROTOCOL_ERROR

This has been happening since approximately February 11, 2026. Cowork was working normally before that date.

What I've Tried (None Resolved the Issue)

1. Full cache clearing:

``
rm -rf ~/Library/Application\ Support/Claude/Cache
rm -rf ~/Library/Application\ Support/Claude/GPUCache
rm -rf ~/Library/Application\ Support/Claude/Code\ Cache
``

1. Deleting Cowork session data:

``
rm -rf ~/Library/Application\ Support/Claude/local-agent-mode-sessions
``

1. Complete nuclear uninstall/reinstall:

``
rm -rf ~/Library/Application\ Support/Claude
rm -rf ~/Library/Caches/com.anthropic.claude*
rm -rf ~/Library/Preferences/com.anthropic.claude*
``

1. Launching with --disable-quic flag:

``
/Applications/Claude.app/Contents/MacOS/Claude --disable-quic
``

1. Sign out / sign in to force new session identity
2. Reinstalled latest version from claude.ai/download
3. Tested on different network (mobile hotspot) — same result

What Should Happen?

Cowork should successfully provision the VM workspace and allow task execution. The workspace was working normally until approximately February 11, 2026.

Is this a regression?

Yes — Cowork was working normally until approximately February 11, 2026.

Error Messages/Logs

net::ERR_QUIC_PROTOCOL_ERROR

From coworkd.log (recurring at every session):
failed to unmount /sessions/[session-name]/mnt/.claude: exit status 32: umount: target is busy.
failed to cleanup cgroup: failed to remove cgroup [id]: remove /sys/fs/cgroup/coworkd/[id]: device or resource busy

Sessions affected: friendly-jolly-carson, quirky-magical-edison

2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] all processes exited, proceeding with cleanup
2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] removed srt-settings /etc/srt-settings/0c3e151e-a65d-478c-95b7-767e0b861c21.json
2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] unmounting /sessions/quirky-magical-edison/mnt/uploads
2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] unmounted /sessions/quirky-magical-edison/mnt/uploads
2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] unmounting /sessions/quirky-magical-edison/mnt/outputs
2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] unmounted /sessions/quirky-magical-edison/mnt/outputs
2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] unmounting /sessions/quirky-magical-edison/mnt/.skills
2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] unmounted /sessions/quirky-magical-edison/mnt/.skills
2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] unmounting /sessions/quirky-magical-edison/mnt/.claude
2026/02/10 19:54:05 [process:0c3e151e-a65d-478c-95b7-767e0b861c21] failed to unmount /sessions/quirky-magical-edison/mnt/.claude: exit status 32: umount: /sessions/quirky-magical-edison/mnt/.claude: target is busy.
2026/02/10 21:53:30 [coworkd] shutting down

Steps to Reproduce

1. Open Claude Desktop on macOS
2. Switch to Cowork tab
3. Workspace setup begins ("Configuration de l'espace de travail de Claude...")
4. Progress reaches ~13%
5. Fails with net::ERR_QUIC_PROTOCOL_ERROR

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

opus 4.6

Claude Code Version

Opus 4.6

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Related Issue

This is the same root cause as #23991 (closed by bot as "not Claude Code"), but Cowork is built on Claude Code's architecture, so filing here as the only available public repo.

Environment

• Platform: macOS (Apple Silicon)
• App: Claude Desktop (latest version as of Feb 13, 2026)
• Plan: Paid (Pro/Max)
• Feature affected: Cowork only — regular Chat works fine, claude.ai in browser works fine