[BUG] Crash when processing Chinese text: byte index not a 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 with a Rust panic when processing Chinese text. The error occurs during string slicing where the byte index falls inside a multi-byte UTF-8 character.

This happens both when:

1. Resuming sessions containing Chinese text (claude --resume)
2. Normal usage with Chinese todo items in the status bar

What Should Happen?

Claude Code should handle Chinese/CJK text without crashing. UTF-8 string operations should use character-aware slicing.

Error Messages/Logs

thread '<unnamed>' panicked at /rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb/library/core/src/str/mod.rs:833:21:
byte index 17 is not a char boundary; it is inside '。' (bytes 15..18) of `是内置命令。`
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5, aborting
Aborted (core dumped)

Steps to Reproduce

1. Start Claude Code and have a conversation in Chinese
2. Exit the session with /exit
3. Run claude --resume --verbose
4. Select the session containing Chinese text
5. Program crashes immediately

Alternative reproduction:

1. Use Claude Code normally with Chinese text
2. When Claude's todo list shows Chinese content in status bar, it may crash

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.3 (Claude Code)

Platform

Anthropic API

Operating System

Ubuntu/Debian Linux

Terminal/Shell

WSL (Windows Subsystem for Linux)

Additional Information

Environment: Windows 11 + WSL2 + Windows Terminal

This bug affects ALL Chinese/CJK users. Multiple issues have been reported:

• #14310
• #15268
• #15394
• #15647
• #15769

The fix is straightforward: use str::floor_char_boundary() or char_indices() instead of raw byte indexing.

I'm a Max subscriber ($100/month) and this makes Claude Code unreliable for daily use in Chinese.