Edit tool fails with EEXIST error on Windows (Git Bash) in v2.1.69

Description

The Edit tool consistently fails with EEXIST: file already exists, mkdir error on Windows when using Git Bash as the shell. This affects all Edit tool calls — no file can be edited.

Environment

• OS: Windows 11 Pro
• Shell: Git Bash (via bash)
• Claude Code version: 2.1.69 (broken), 2.1.61 (works fine)
• Node.js: bundled with Claude Code

Steps to Reproduce

1. Install Claude Code v2.1.69 on Windows with Git Bash as the default shell
2. Attempt any Edit tool operation on any file

Expected Behavior

The Edit tool should successfully modify the file.

Actual Behavior

Every Edit call fails with:

EEXIST: file already exists, mkdir

Root Cause Analysis

The issue appears to be in how path.dirname() handles Windows backslash paths inside Git Bash's POSIX environment.

In Git Bash on Windows:

path.dirname('C:\Foo\Bar\file.txt')
// Returns: 'C:' (incorrect — treats entire backslash path as filename)
// Expected: 'C:\Foo\Bar'

This causes mkdirSync('C:') to be called, which fails with EEXIST because C: already exists as a drive root.

Additionally, the broken path handling creates junk directories in the working directory with concatenated path segments (e.g., a directory named Projectskurumsalxhaberv4KurumsalxHaberLib appeared in the repo root).

Workaround

Downgrading to v2.1.61 resolves the issue:

claude install 2.1.61

Additional Context

• The issue is specific to the combination of Windows + Git Bash
• v2.1.61 does not have this problem, suggesting a regression was introduced in a later version
• The path module behavior differs between native Windows Node.js and Git Bash's POSIX layer — path.dirname() needs to handle both forward and backslash separators correctly