[BUG] VS Code Extension hangs indefinitely - process spawns but never registers IDE lock or responds (macOS darwin-arm64)

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

Claude Code extension version: 2.1.63
VS Code version: Visual Studio Code 2.app (latest stable)
OS: macOS darwin-arm64 (Apple Silicon)
Platform: darwin-arm64

What's Wrong?

The Claude Code VS Code extension intermittently hangs indefinitely after sending a message. The spinner shows but no response ever arrives or arrives after 8+ minutes. The CLI works correctly at all times.
After extensive debugging, the specific failure mode is:

• Extension spawns the Claude process successfully
• The process never writes a lock file to ~/.claude/ide/
• The process writes no output to ~/.claude/debug/latest (the symlink is not updated)
• The process dies silently with no error in the extension output log
• The extension UI shows the "Germinating/Clauding" spinner indefinitely

This is intermittent — sometimes it works, sometimes it doesn't. It can fail immediately after a working session with no changes to the environment.

What Should Happen?

Claude should respond to the message within a few seconds.

Error Messages/Logs

**Double spawn at identical millisecond:**
Spawning Claude... cwd: /Users/myuser/myproject, version: 2.1.63 [x2 same timestamp]
Both processes race to write ~/.claude.json simultaneously.

**Lock file PID mismatch:**
Filename: ~/.claude/ide/55667.lock
Contents: {"pid":62772,...}
PID 62772 is the VS Code Electron process itself, not Claude.

**Every session:**
[ERROR] MCP server "claude-vscode" Failed to fetch tools: MCP error -32601: Method not found

Steps to Reproduce

1. Open VS Code with the Claude Code extension installed
2. Open a new chat with the + button
3. Send any message (e.g. "Hello")
4. Observe: spinner runs indefinitely, no response

What I've Tried

Clean uninstall and reinstall of extension via VS Code marketplace
Removed old Cursor extension versions (~/.cursor/extensions/anthropic.claude-code-2.1.44 and 2.1.45) that were being picked up by VS Code
Re-authenticated via claude auth logout + claude auth login
Deleted stale sessions from ~/.claude/projects/
Killed all orphaned native-binary/claude processes
Deleted stale lock files from ~/.claude/ide/
Changed claudeCode.preferredLocation from "panel" to "sidebar"
Confirmed binary works correctly when run directly:

$ ~/.vscode/extensions/anthropic.claude-code-2.1.63-darwin-arm64/resources/native-binary/claude --version
2.1.63 (Claude Code)
None of these resolved the issue.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.63

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

VS Code integrated terminal

Additional Information

The CLI (claude in terminal) works correctly at all times
When the extension does work, it works well — the issue is purely intermittent
The first successful response after a hang can take 8+ minutes
Related issues: #25253, #27820
Appears related to the multi-client stdio race condition acknowledged in the 2.0.61 changelog