[BUG] --worktree <name> silently falls back to parent repo cwd when worktree name already exists

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?

claude -w/--worktree <name> is documented as "Create a new git worktree for this session". When the requested name collides with an existing worktree at .claude/worktrees/<name>/, the flag neither attaches to it nor errors visibly — the session silently starts bound to the parent repo's cwd (and parent's checked-out branch). Any edits land on the parent branch, giving the impression the worktree was selected when it wasn't.

What Should Happen?

One of:

• Attach to the existing worktree of that name and chdir into it, or
• Fail loudly with a message like:

``
Error: worktree 'bugfix-blocker' already exists at <path>.
cd into it and run claude, or choose a different name.
``

Error Messages/Logs

Steps to Reproduce

1. Have a worktree at .claude/worktrees/bugfix-blocker/ (branch worktree-bugfix-blocker) — created from a previous claude --worktree bugfix-blocker session, for example.
2. From the parent repo (on a different branch, e.g. test):

``bash
cd /path/to/repo
claude --worktree bugfix-blocker
``

1. Inside the new session:

``bash
pwd # → /path/to/repo (parent, NOT the worktree)
git branch --show-current # → test (parent's branch)
``

1. Any file edits go to test, not worktree-bugfix-blocker.

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.128 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

iTerm2

Additional Information

_No response_