[BUG] Filesystem Breakoff

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?

Adding a data point from my own troubleshooting session (Windows 11, build 26200.8655, Claude 1.15962.0.0 MSIX/Store install):

• Confirmed only one claude_desktop_config.json exists (at %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\) — no stale duplicate
• Confirmed no stuck node/claude processes via Get-Process
• Confirmed no port conflicts on 3000-3999 via Get-NetTCPConnection
• Same large file read (~15KB TypeScript file) via Filesystem MCP hung for the full 4-minute timeout 3 times consecutively, then succeeded instantly on a later retry with zero changes made in between
• This rules out the usual local-environment causes and points at session/transport state inside the Desktop client itself

What Should Happen?

Adding a data point from my own troubleshooting session (Windows 11, build 26200.8655, Claude 1.15962.0.0 MSIX/Store install):

• Confirmed only one claude_desktop_config.json exists (at %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\) — no stale duplicate
• Confirmed no stuck node/claude processes via Get-Process
• Confirmed no port conflicts on 3000-3999 via Get-NetTCPConnection
• Same large file read (~15KB TypeScript file) via Filesystem MCP hung for the full 4-minute timeout 3 times consecutively, then succeeded instantly on a later retry with zero changes made in between
• This rules out the usual local-environment causes and points at session/transport state inside the Desktop client itself

Error Messages/Logs

Steps to Reproduce

Adding a data point from my own troubleshooting session (Windows 11, build 26200.8655, Claude 1.15962.0.0 MSIX/Store install):

• Confirmed only one claude_desktop_config.json exists (at %LOCALAPPDATA%\Packages\Claude_pzs8sxrjxfjjc\LocalCache\Roaming\Claude\) — no stale duplicate
• Confirmed no stuck node/claude processes via Get-Process
• Confirmed no port conflicts on 3000-3999 via Get-NetTCPConnection
• Same large file read (~15KB TypeScript file) via Filesystem MCP hung for the full 4-minute timeout 3 times consecutively, then succeeded instantly on a later retry with zero changes made in between
• This rules out the usual local-environment causes and points at session/transport state inside the Desktop client itself

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

Claude 1.15962.0.0

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_