[BUG] Diff tool selection is not remembered

Environment

• Platform (select one):
• [x] Anthropic API
• [ ] AWS Bedrock
• [ ] Google Vertex AI
• [ ] Other: <!-- specify -->
• Claude CLI version: 1.0.3
• Operating System: macOS 15.4.1
• Terminal: PHPStorm's terminal, iTerm2

Bug Description

Diff tool selection on a project level is not remembered between sessions. I have to use /config and select the diff tool every time.

Steps to Reproduce

1. claude
2. /config -> change diff tool from auto to terminal
3. exit
4. claude
5. /config
6. Observe that diff tool is set to auto

Expected Behavior

The selection of the diff tool is preserved.

Actual Behavior

The diff tool is reset to auto

Additional Context

This is extremely annoying and disruptive, because Claude keeps opening files in IDE interrupting my flow.

Maybe there is already a config/setting somewhere, but I could not find any docs about this.