[BUG] Claude Code intermittently switches between Update and Edit tools for files with no way to enforce Update only

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?

For most of my workflow experience, Claude Code uses its Update tool for modifying files. In this mode, it shows you a diff before you accept with Yes / No.

Sometimes, without warning, it starts to use its Edit tool, which only shows you a path to the file it wants to change, without warning you ahead of time what diff it wants to apply. Only after you accept the Edit does it show you the diff it applied after-the-fact.

What Should Happen?

I expect to be able to force Claude Code to use Update only and never Edit mode. I need to review diffs ahead of time before accepting them. This breaks my workflow badly and it feels like a bug that I can't force Claude to use Update instead of Edit. Restarting my claude session often fixes it.

Error Messages/Logs

Steps to Reproduce

I have no way of replicating this behavior reliably. Most of the time it uses Update mode when working, but without warning it switches to Edit with no way to get back until I restart Claude Code.

Claude Model

Sonnet (default)

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.39 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

Xterm

Additional Information

_No response_