[BUG] --worktree flag fails with EEXIST on second worktree creation (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?

When using claude --worktree <name> on Windows, the first worktree is created successfully, but every subsequent call fails with:

Error creating worktree: EEXIST: file already exists, mkdir 'C:\users\lucho\desktop\SISTEMASDATIX\.claude\worktrees'

The error is on the parent directory .claude\worktrees, not on the new worktree itself. The parent already exists from the first worktree creation, and the code tries to create it again without checking.

What Should Happen?

Each claude --worktree <name> call should create only the new subdirectory .claude\worktrees\<name>, without trying to recreate the parent .claude\worktrees every time. The fix would be using mkdir with { recursive: true } or checking if the directory already exists first.

Error Messages/Logs

Error creating worktree: EEXIST: file already exists, mkdir

'C:\users<user><project>.claude\worktrees'

The error is on the **parent directory** `.claude\worktrees`, not on the new 
worktree itself. The parent already exists from the first worktree creation, and 
the code tries to create it again without checking.

Steps to Reproduce

1. Open a project with a git repo
2. Run claude --worktree first-task → ✅ works
3. Run claude --worktree second-task → ❌ EEXIST error

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.186 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Warp

Additional Information

The --worktree implementation calls mkdir('.claude/worktrees') unconditionally
instead of mkdir('.claude/worktrees', { recursive: true }) or checking if the
directory already exists first. On Windows, mkdir throws EEXIST on existing
directories instead of silently succeeding (unlike POSIX).

Related to other EEXIST/Windows issues: #37306, #31030, #55427

Environment

• Claude Code version: 2.1.186
• OS: Windows 11
• Terminal: Warp
• Shell: PowerShell