[BUG] Desktop (Windows): session worktree creation fails with "already exists" because the worktree path is sent without the drive letter (/work/... instead of C:/work/...)

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?

On Windows, creating a session worktree through the Claude desktop app fails with:

git worktree add failed: Preparing worktree (new branch 'claude/<slug>') fatal: '/work/myrepo/.claude/worktrees/<slug>' already exists (reported by the remote host)

The repository is at C:\work\myrepo (path anonymized). The path in the error has lost its drive letter. Afterwards the target folder does not exist, and every failed attempt leaves a branch claude/<slug> that points at HEAD with 0 commits. On 2026-10-15 this happened 4 times within 10 minutes on the same repo (4 orphan branches).

What I could pin down:

1. The path passed to git worktree add is drive-less: /work/myrepo/.claude/worktrees/<slug> instead of C:/work/myrepo/.claude/worktrees/<slug>. (On 2026-09-02 ~/.claude/remote/run/*/remote-server.log also showed chdir \work\myrepo/.claude/worktrees/....)
2. The target folder is created empty before git worktree add runs (seen on 2026-09-02).
3. Git for Windows 2.45.1, given a drive-less absolute path, reports the empty pre-created folder as "already exists". It succeeds when the path has the drive letter, or when the folder is not pre-created (tested 2026-09-02). Step 3 was re-tested today with the commands under Steps to Reproduce.
4. After the failure the folder is removed, so only the orphan branch remains.

What Should Happen?

The worktree path should keep its drive letter (C:/work/myrepo/.claude/worktrees/<slug>) so the worktree is created. A failed attempt should not leave a 0-commit orphan branch behind.

Error Messages/Logs

git worktree add failed: Preparing worktree (new branch 'claude/<slug>') fatal: '/work/myrepo/.claude/worktrees/<slug>' already exists (reported by the remote host)

Steps to Reproduce

1. Windows 11, git repository on drive C: (e.g. C:\work\myrepo), Git for Windows 2.45.1.
2. Start a session on that repository with worktree isolation in a way that goes through the desktop app's host bridge. Seen with:

a) a session started on this PC from another device (Remote Control) with worktree isolation (2026-09-02), and
b) a session started from a "start a new session" suggestion card in the desktop app with its own worktree (2026-10-15).

1. The session fails to start with the error above; git branch --list "claude/*" shows a new 0-commit branch, and there is no folder under .claude\worktrees.

Step 3 of the cause alone, PowerShell at the repo root:

New-Item -ItemType Directory .claude\worktrees\x
git worktree add "/work/myrepo/.claude/worktrees/x" -b t/x
# fatal: '/work/myrepo/.claude/worktrees/x' already exists   (branch t/x is still created)

Claude Model

Not sure / Multiple models

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude desktop app 2.37337.1 (MSIX), bundled Claude Code 2.1.295; standalone CLI 2.1.263 also installed

Platform

Other

Operating System

Windows

Terminal/Shell

Other

Additional Information

• Windows 11 (10.0.26200), Git for Windows 2.45.1.windows.1, claude.ai subscription through the Claude desktop app (Code tab).
• Version note: the desktop app's bundled Claude Code is 2.1.295; npm latest is 2.1.300.
• Workaround: open the session without worktree isolation (repository root), then create the worktree from inside the session with a full path (git worktree add C:/work/myrepo/.claude/worktrees/<name> -b <branch>); that works every time.
• Cleanup needed after each failure: git branch -d claude/<slug> for the 0-commit branch.