[BUG] Diff panel opens automatically in fullscreen mode without running /diff

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?

Since the diff panel was introduced in v2.1.260, it opens on its own beside the conversation in fullscreen mode without me ever running /diff. The changelog describes the panel as something you toggle with /diff, but in my sessions it appears unprompted whenever there are uncommitted changes in the working tree (e.g., untracked files created during the session).

Example: when I created a directory with 4 untracked files, a panel appeared on the side showing "4 files changed" with a per-file breakdown ("New file not yet staged. Run git add ... to see line counts") and a "+N files edited before this session (show)" footer — with no /diff invocation from me at any point in the session.

I can close it with the ✕ or by running /diff. It doesn't reappear when I exit and restart the session.

What Should Happen?

The diff panel should only open when explicitly toggled with /diff, per the v2.1.260 changelog entry ("Added a diff panel that opens beside the conversation in fullscreen mode and shows your uncommitted changes as Claude edits; toggle it with /diff"). Alternatively, if auto-opening is intended behavior, there should be a setting to disable it so it stays closed.

Error Messages/Logs

Steps to Reproduce

1. Create new untracked files in a git repo
2. Start claude in fullscreen mode inside that repo
3. Observe the diff panel opens on the side automatically, without /diff being run

Claude Model

Opus

Is this a regression?

No, this never worked

Last Working Version

N/A

Claude Code Version

2.1.266 (Claude Code)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_