[BUG] Panic on UTF-8 character boundary with Arabic text

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?

Describe the bug
Claude Code panics when processing strings containing Arabic characters. The panic occurs when the code attempts to slice a UTF-8 string at a byte index that falls in the middle of a multi-byte character.

Context
Working with content containing Arabic text ("أولوية السلامة" - "Safety Priority") as part of a skill that includes multilingual quotes. The crash occurred during string processing/truncation.

Expected behavior
Claude Code should handle UTF-8 strings with multi-byte characters (Arabic, Chinese, emoji, etc.) without panicking. String slicing should use character boundaries, not raw byte indices.

Additional context
The panic handler itself failed (error 5), causing an abort rather than a graceful error message. This suggests the panic recovery mechanism also has issues.

What Should Happen?

Expected behavior
Claude Code should handle UTF-8 strings with multi-byte characters (Arabic, Chinese, emoji, etc.) without panicking. String slicing should use character boundaries, not raw byte indices.

Additional context
The panic handler itself failed (error 5), causing an abort rather than a graceful error message. This suggests the panic recovery mechanism also has issues.

Error Messages/Logs

Error message
thread '' (1652572) panicked at /rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb/library/core/src/str/mod.rs:833:21:
byte index 46 is not a char boundary; it is inside 'ة' (bytes 45..47) of  "Arabic Proverb", "أولوية السلامة", "Nothing
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

Environment

OS: macOS (Darwin 25.2.0)
Claude Code version: (please add your version from claude --version)
Shell: zsh

Steps to Reproduce

Claude Code
Error message
thread '' (1652572) panicked at /rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb/library/core/src/str/mod.rs:833:21:
byte index 46 is not a char boundary; it is inside 'ة' (bytes 45..47) of "Arabic Proverb", "أولوية السلامة", "Nothing
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

Environment

OS: macOS (Darwin 25.2.0)
Claude Code version: (please add your version from claude --version)
Shell: zsh

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.76

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_