Write tool EEXIST error when writing to existing directories on Windows

Description

The Write tool fails with EEXIST: file already exists, mkdir '<path>' when creating new files in any existing subdirectory on Windows. The tool internally calls fs.mkdir() on the parent directory before writing, but does not use { recursive: true }, causing it to throw when the directory already exists.

Reproduction Steps

1. Have any existing subdirectory in your project (e.g., docs/, src/, etc.)
2. Use the Write tool to create a new file in that directory:

• Write file_path: K:\Workspace\MyProject\docs\new-file.md

1. Error: EEXIST: file already exists, mkdir 'K:\Workspace\MyProject\docs'

Test Matrix

| Scenario | Result |
|----------|--------|
| Write to project root (parent = repo root) | SUCCESS |
| Write to any existing subdirectory (docs/, bot/, cloudflare/) | EEXIST ERROR |
| Write to existing nested subdirectories (docs/reviews/, docs/audit/) | EEXIST ERROR |
| Write to a brand-new directory that doesn't exist yet | SUCCESS (mkdir creates it) |
| Bash echo > to same directories | SUCCESS (filesystem is fine) |

Root Cause

The Write tool's internal fs.mkdir() call on the parent directory path does not use { recursive: true }. Without that flag, mkdir throws EEXIST when the target directory already exists. With { recursive: true }, it silently succeeds (equivalent to mkdir -p).

Expected Behavior

The Write tool should create files in any directory — existing or new — without errors.

Suggested Fix

Change the internal fs.mkdir(parentDir) to fs.mkdir(parentDir, { recursive: true }).

Environment

• Platform: Windows 11 Pro 10.0.26200
• Shell: Git Bash
• Claude Code model: claude-opus-4-6