Write tool fails with EEXIST error on paths containing non-ASCII (Japanese) characters on Windows

Bug Description

The Write tool fails with an EEXIST error when the file path contains non-ASCII characters (specifically Japanese characters). This was working previously and appears to be a regression.

Error Message

EEXIST: file already exists, mkdir 'D:\日本語パス\project'

Steps to Reproduce

1. Have an existing directory with Japanese characters in the path (e.g., D:\日本語パス\project\)
2. Use the Write tool to create a new file in that directory:

• file_path: D:/日本語パス/project/write_test.txt
• content: any text content

1. The tool fails with the EEXIST error

Expected Behavior

The file should be created successfully, as it was working before.

Actual Behavior

The Write tool throws EEXIST: file already exists, mkdir 'D:\日本語パス\project' and fails to create the file.

Additional Context

• Platform: Windows 11 Home 10.0.26200
• Shell: bash
• Writing to a path without Japanese characters (e.g., D:/newfile/write_test.txt) works fine
• Using Bash tool with printf > "D:/日本語パス/project/write_test.txt" as a workaround also works fine
• The Read tool works correctly with the same Japanese path
• The issue appears to be in the fs.mkdir call within the Write tool's directory creation logic — the recursive: true option may not be functioning correctly for non-ASCII paths on Windows

Workaround

Use the Bash tool to write files to paths containing non-ASCII characters instead of the Write tool.