[BUG] Edit tool fails in subdirectories (works in root directory)

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?

Summary

I've discovered a specific pattern for the "File has been unexpectedly modified" error that hasn't been documented yet: The Edit tool consistently fails in subdirectories but works perfectly in the root directory.

Environment

• Platform: Windows (MINGW64_NT-10.0-26200)
• Claude Code Version: 2.0.74
• File System: NTFS
• Shell: Git Bash

What Should Happen?

The file should be edited successfully.

Error Messages/Logs

Steps to Reproduce

Reproduction Steps

Setup

cd "C:/path/to/your/project"
echo "line 1" > root_test.txt
mkdir -p subdirectory
echo "line 1" > subdirectory/subdir_test.txt

Test 1: Edit file in ROOT directory (✅ WORKS)

Read: C:/path/to/your/project/root_test.txt
Edit: Change "line 1" to "line 1 EDITED"
Result: ✅ SUCCESS - File edited successfully

Test 2: Edit file in SUBDIRECTORY (❌ FAILS)

Read: C:/path/to/your/project/subdirectory/subdir_test.txt
Edit: Change "line 1" to "line 1 EDITED"
Result: ❌ ERROR - "File has been unexpectedly modified"

Comprehensive Testing Results

I tested multiple scenarios to isolate the cause:

| Test Scenario | Root Directory | Subdirectory |
|--------------|----------------|--------------|
| Small text file (33 bytes) | ✅ Works | ❌ Fails |
| Large HTML file (43KB) | ✅ Works | ❌ Fails |
| Freshly created file | ✅ Works | ❌ Fails |
| File copied from subdirectory | ✅ Works | ❌ Fails |
| .txt extension | ✅ Works | ❌ Fails |
| .html extension | ✅ Works | ❌ Fails |
| .md extension | ✅ Works | ❌ Fails |
| Different subdirectory names | ✅ Works | ❌ Fails |

Key Findings

What DOESN'T cause the issue

• ❌ File sync services (OneDrive disabled)
• ❌ Antivirus software (disabled during testing)
• ❌ File size
• ❌ File type/extension
• ❌ Directory permissions (identical between root and subdirectories)
• ❌ Specific directory names
• ❌ External processes modifying files

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.74 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

Root Cause Hypothesis

The Edit tool's file change detection mechanism appears to have a path resolution or file watcher bug that breaks when working with files in subdirectories. The issue is likely in how the tool:

1. Stores the initial file state during Read operation
2. Retrieves the file path for comparison during Edit operation
3. Compares file metadata (timestamps/checksums) between operations

The discrepancy between root and subdirectory behavior suggests the tool may be:

• Using different path formats (relative vs absolute)
• Having path normalization issues (forward slashes vs backslashes)
• Accessing different file handles or inodes for the same file

Workaround

Confirmed workaround: Move files to the root directory temporarily for editing:

# Move to root
mv subdirectory/file.html ./

# Claude can now edit successfully
# (Edit operations work)

# Move back
mv file.html subdirectory/

Additional Evidence

File system timestamps show no external modifications:

# File in subdirectory (fails to edit)
stat subdirectory/subdir_test.txt
Access: 2025-12-20 11:32:xx
Modify: 2025-12-20 11:32:xx
Change: 2025-12-20 11:32:xx

# No changes between Read and Edit operations