[BUG] Cowork (Windows): project context folders never mount in new sessions; Add-folder dialog cannot confirm — reproduced on two machines after latest update

TL;DR for maintainers: Since the July 8 update, Cowork on Windows silently detaches any connected folder that contains another connected folder. Connected folders "dropping" mid-session is cloud execution mode, not nested folders. Cloud sessions reach the desktop over a bridge that drops; the folder card stays false-green "attached" while file tools silently die. Workaround: Settings → Cowork → "Run new tasks in the cloud" → OFF (global; new tasks only). Root causes to fix: (1) cloud-on default is generating the volume; (2) UI shows "attached" when the bridge is dead — should show a broken state. Nesting and symlinks are ruled out.

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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

• App: Claude Desktop (Cowork mode), version 1.19367.0 (Electron 42.5.1)
• OS: Windows 11 Pro, both machines
• Plan: Max (20x)
• Started: July 8, 2026, immediately after the desktop app update (the one that also enabled mobile Cowork). Second machine received the same update July 9 and broke within the hour.

Summary

Since the update, Cowork folder mounts are completely broken:

1. Projects still show their context folders in the Context panel, but every new session starts with zero folders actually attached. Claude confirms from inside the session that connectedFolders is empty on the device bridge.
2. Re-adding is impossible: in the Add folder dialog, when the folder list already contains an entry, the confirm action is dead — Enter and the confirm button do nothing. No error is shown.

Steps to reproduce

1. Open an existing Cowork project that has a context folder attached (visible in the Context panel)
2. Start a new session in that project (any first message)
3. Ask Claude to list the connected folder → it reports no folders are connected to the device
4. Click + → Add folder, select the folder → the dialog will not confirm

Expected

New sessions inherit the project's context folders and mount them; Add folder attaches a folder mid-session.

Actual

Sessions start with nothing attached despite the UI showing the folder; Add folder silently refuses to confirm. get_device_info from the session shows "connectedFolders": [] while the project UI shows the folder as attached.

Ruled out (extensive troubleshooting)

• Full app quit (from tray) and relaunch — no change
• Full PC reboot — no change
• Sign out / sign back in — no change (state appears device-local)
• Windows privacy settings: File system access ON, Documents library access ON, per-app access ON
• Windows Controlled folder access: OFF
• Account mix-up: same account everywhere, verified in Settings → Account
• Not machine-specific: reproduced on a second Windows 11 PC, different account, untouched configuration — identical symptoms starting within an hour of that machine receiving the update

Additional diagnostics

• The device bridge itself is healthy: get_device_info responds normally, and the Filesystem MCP extension works perfectly (Claude can list/read/write the same directories through it). Only the native Cowork folder-mount path is broken — this isolates the failure to mount registration/attachment, not device connectivity or OS file permissions.
• Around the same time, unexplained OS-native-looking folder access prompts appeared, and plan usage meters displayed inconsistently (weekly usage showing 94%/100% used, then 0% with a different reset time ~15 minutes later after an app restart).

Possibly related

• #76183 — folder mount unavailable until after first message. May be the same underlying change, but our failure persists after the first message: the Add-folder confirm stays dead mid-session whenever the list already has an entry.

Impact

All project-based Cowork workflows relying on connected folders are unusable. Current workaround is routing all file access through the Filesystem MCP extension, which bypasses native mounts entirely (no staging/commit, no local sandbox shell).

What Should Happen?

New sessions should inherit and mount the project's context folders automatically, and the Add folder dialog should let me confirm a selected folder and attach it mid-session. Both worked exactly this way before the July 8 update.

Error Messages/Logs

Steps to Reproduce

Every new session starts with zero folders attached even though the project's Context panel shows them. The device reports "connectedFolders": [] from inside the session. In the Add folder dialog, when the folder list already contains an entry, Enter and the confirm button do nothing — no error, the folder just never attaches.

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

1.19367.0

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_