[BUG] Claude Code VSCode extension webview "Not responding" on Windows 11 - terminal works, GUI does not

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

• OS: Windows 11 Pro 25H2 (Build 26200.8039)
• Claude Code extension: v2.1.85
• VSCode version: 1.113.0 (user setup) — Electron 39.8.3, Chromium 142.0.7444.265, Node.js 22.22.1
• Claude CLI: v2.1.85
• Project drive: C: (NTFS) — also reproduced on F: DevDrive (ReFS)

Bug Description

The Claude Code VSCode extension webview consistently shows "Not responding" when sending messages through the GUI panel. The terminal-based interface within the same extension works correctly. The CLI (claude) also works normally.

Steps to Reproduce

1. Install Claude Code extension v2.1.85 on Windows 11
2. Open any project in VSCode
3. Click "New Session" in the Claude Code panel
4. Type any message and send
5. Webview shows "Not responding · try stopping" indefinitely

Expected Behavior

Webview responds normally like the terminal interface.

What Works

• Claude CLI in terminal
• Claude Code terminal interface (within the extension)
• Claude Code web (claude.ai/code)

What Doesn't Work

• Claude Code VSCode extension webview (GUI panel)

Logs

Ctrl+Shift+U → Claude Code output shows ide_backend_stall_detected with idleMs: 60000+ after every message attempt.

Additional Context

Tried full reinstall (npm uninstall/install, extension uninstall/reinstall, cleared globalStorage and .claude config) — issue persists across fresh installs.

Related issues: #39229 (heartbeat timeout), #39183 (WSL2 WebSocket loop)

What Should Happen?

The Claude Code VSCode extension webview responds normally like the terminal interface does — messages are sent, processed, and responses are displayed in the GUI panel.

Error Messages/Logs

ide_backend_stall_detected {"idleMs":60000}
(repeated after every message attempt — visible in Ctrl+Shift+U > Claude Code output panel)

Steps to Reproduce

1. Install Claude Code extension v2.1.85 on Windows 11 Pro 25H2
2. Open any project folder in VSCode 1.113.0
3. Open the Claude Code panel (sidebar)
4. Click "New Session"
5. Type any message and press Enter or click Send
6. Webview shows "Not responding · try stopping" indefinitely
7. Check output panel (Ctrl+Shift+U > Claude Code): ide_backend_stall_detected {"idleMs":60000} appears

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.1.85 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_