[BUG] MCP Filesystem extension — UtilityProcess spawn timeout on Windows

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?

The Filesystem MCP extension consistently fails to connect with a UtilityProcess spawn timeout error. The MCP server process starts successfully but takes ~8–10 seconds to report ready, while Claude Desktop's hardcoded UtilityProcess timeout fires after ~5 seconds — causing the connection to be dropped before the server is usable.

What Should Happen?

The Filesystem extension connects successfully and is available for use in conversations.

Error Messages/Logs

2026-03-17 17:43:15 [info] Launching MCP Server: Filesystem
2026-03-17 17:43:15 [info] Using UtilityProcess for extension Filesystem: appConfig.isUsingBuiltInNodeForMcp is true
2026-03-17 17:43:20 [error] Failed to start UtilityProcess: UtilityProcess spawn timeout ← fires at +5s
2026-03-17 17:43:23 [info] [UtilityProcess stderr] Secure MCP Filesystem Server running on stdio ← server ready at +8s

Steps to Reproduce

1. Install Claude Desktop v1.1.7053 via Windows Store on Windows 11
2. Install the Filesystem extension from the Connectors panel
3. Configure at least one allowed directory
4. Observe the error notifications on startup: "Could not connect to MCP server Filesystem" and "MCP Filesystem: UtilityProcess spawn timeout"

Claude Model

None

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

Claude Desktop v1.1.7053 (Windows Store / MSIX package)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Non-interactive/CI environment

Additional Information

Environment

• Product: Claude Desktop v1.1.7053 (Windows Store / MSIX package)
• OS: Windows 11 x64
• Extension: Filesystem v0.2.0 (ant.dir.ant.anthropic.filesystem)
• Node.js (system): v22.22.0
• Node.js (Claude built-in): v24.13.0

Workarounds attempted (all failed)

• Reinstalling the extension
• Cleaning claude_desktop_config.json and re-adding via UI
• Uninstalling and reinstalling Claude Desktop
• Adding Windows Defender exclusion for the Claude WindowsApps folder
• Manual claude_desktop_config.json entry using absolute node.exe path
• Killing all Claude processes before restart

Root cause hypothesis

The UtilityProcess spawn timeout is hardcoded and too short for this environment. The MSIX packaging (Windows Store) appears to add overhead to child process startup — the server starts successfully but consistently exceeds the timeout window. A configurable timeout (similar to MCP_TIMEOUT in Claude Code CLI) would resolve this.

Related issues

• anthropics/claude-code#22542 — "Make MCP Tool Execution Timeout Configurable in Claude Desktop"
• anthropics/claude-code#22299 — "MCP tool call responses dropped by client (Windows, regression in CCD v2.1.22)"

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