[BUG] Rust panic when handling Arabic text - byte index not on char boundary

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?

Claude Code crashes (panics) when processing Arabic text in code comments or console output. The Rust code is indexing into a UTF-8 string at a byte position that falls in the middle of a multi-byte Arabic character, causing an immediate panic and complete crash of the CLI.

What Should Happen?

Claude Code should handle multi-byte UTF-8 characters (Arabic, Chinese, Hebrew, Persian, etc.) correctly without crashing. The string slicing should use character boundaries, not byte boundaries.

Error Messages/Logs

thread '<unnamed>' panicked at /rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb/library/core/src/str/mod.rs:833:21:
byte index 7 is not a char boundary; it is inside 'ر' (bytes 6..8) of 'state تقرير (من الـ'
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5, aborting
zsh: abort      claude

Steps to Reproduce

1. Open a React/TypeScript project
2. Edit a JavaScript file containing Arabic text in console.log:

   console.log('✅ تم تحديث الملاحظة في الـ state:', { observationId, updates });

1. Let Claude Code process and display the changes
2. Claude Code crashes immediately when trying to slice/display the Arabic string

Claude Model

Opus

Is this a regression?

Yes, this worked in a previous version

Last Working Version

_No response_

Claude Code Version

2.0.76

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

This is a UTF-8 string slicing bug in Rust. Arabic characters use 2 bytes each in UTF-8 encoding. The code attempts to slice at byte index 7, which falls in the middle of the Arabic character 'ر' (bytes 6-8).

This issue affects:

• Arabic speakers
• Hebrew speakers
• Persian/Farsi speakers
• Urdu speakers
• Potentially Chinese, Japanese, Korean users

The fix should use Rust's .chars() iterator or .char_indices() instead of direct byte indexing when slicing strings that may contain non-ASCII characters.