[BUG] Edit tool fails with "File has been unexpectedly modified" when file hasn't changed (Windows)

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?

Description:

The Edit tool consistently fails with the error "File has been unexpectedly modified. Read it again before attempting to write it." even when:

• No editors are open
• No dev servers or file watchers running
• No manual edits being made
• File timestamp remains unchanged between Read and Edit calls

The issue accumulates over a session and temporarily resolves after restarting the PC.

Environment:

• OS: Windows 11
• Claude Code version: Latest (installed via npm)
• Node.js version: 18+
• Working directory: C:\Users\[username]
• Target files: D:\Work\[project] (different drive)

Observed Behavior:
```

● Read(D:\Work\project\src\file.ts)
⎿  Error reading file

● # Read succeeds
Read file D:/Work/project/src/file.ts

# Immediate Edit fails
Edit tool error: "File has been unexpectedly modified. Read it again before attempting to write it."

# Verify file wasn't modified
$ stat file.ts | grep Modify
Modify: 2026-01-12 04:04:01.268346800 -0800 # Timestamp unchanged

Verification that file is stable:
# File timestamp doesn't change on its own
$ stat file.ts | grep Modify
Modify: 2026-01-12 04:04:01.268346800 -0800

$ sleep 5

$ stat file.ts | grep Modify
Modify: 2026-01-12 04:04:01.268346800 -0800 # Same

Additional observations:

• Happens on ALL files after the bug starts occurring (tested .ts, .tsx, .json files)
• sed commands via Bash tool work fine as a workaround
• The Write tool (full file replacement) may also work
• Cross-drive scenario: Working directory on C:, files on D: drive
• Restarting PC temporarily fixes the issue
• Issue returns after ~30-60 minutes of usage

Expected Behavior:
Edit tool should succeed when the file hasn't been modified between Read and Edit calls.

Workarounds:

• Use sed via Bash tool for edits
• Restart Claude Code / PC
• Provide full file content for manual pasting

Possible Causes:

• File hash/checksum tracking getting corrupted over time
• Windows NTFS timestamp precision issues
• Cross-drive path handling issues
• Memory/state leak in file tracking

What Should Happen?

Edit tool should succeed when the file hasn't been modified between Read and Edit calls.

Error Messages/Logs

Error: File has been unexpectedly modified. Read it again before attempting to write it.

Steps to Reproduce

1. Use Claude Code for an extended session (30+ minutes)
2. Read a file using the Read tool
3. Immediately attempt to Edit the same file
4. Error occurs even with no external modifications

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.5 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

IntelliJ IDEA terminal

Additional Information

tried it also on powershell terminal same thing