[BUG] "File has been unexpectedly modified"

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?

Title: Edit/Write tools fail with "File has been unexpectedly modified" after Read due to system-reminder injection

Description:

When attempting to edit a file using the Edit or Write tools, the operation fails repeatedly with one of these errors:

• "File has been unexpectedly modified. Read it again before attempting to write it."
• "File has not been read yet. Read it first before writing to it."

This occurs even immediately after a successful Read operation on the same file.

Steps to reproduce:

1. Read a file using the Read tool
2. Immediately attempt to Edit or Write to that file
3. Error: "File has been unexpectedly modified"
4. Read the file again
5. Attempt Edit/Write again
6. Same error - infinite loop

Root cause (suspected):

The <system-reminder> tags that are injected into tool results appear to mark the file as "modified" from the tool's perspective, even though the actual file content hasn't
changed. Each Read operation triggers a system-reminder injection, which then invalidates the read state.

Workaround:

Create a new file with a different name using Write, then use Bash mv to replace the original:
# Instead of editing original.py directly:
Write new content to original_v2.py
mv original_v2.py original.py

Environment:

• Platform: Windows (MINGW64_NT-10.0)
• Claude Code CLI

Impact:

• Significant time wasted in loops (10+ retry attempts)
• Poor user experience
• Forces use of workaround for basic file editing

---

What Should Happen?

Claude should be able to edit any of the code files

Error Messages/Logs

Steps to Reproduce

I don't know, it happens sometimes but not always

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

Claude Code 2.0.57

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

Windows Terminal

Additional Information

_No response_