Crash when editing Markdown files with Chinese text (byte boundary error)

Claude Code crashes frequently when editing Markdown files containing Chinese text.

Error

thread '<unnamed>' panicked at library/core/src/str/mod.rs:833:21:
byte index 120 is not a char boundary; it is inside '表' (bytes 118..121)
fatal runtime error: failed to initiate panic, error 5, aborting
zsh: abort      claude

Environment

• Version: 2.0.73
• OS: macOS (Darwin 25.1.0)
• Locale: zh_CN.UTF-8
• Files: UTF-8 encoded

When it happens

• Trigger: When executing file edit commands on Markdown files with Chinese content
• Frequency: Started happening frequently after updating to 2.0.73
• Use case: Editing documents with tables containing longer Chinese text (e.g., PRD documents)

Root cause

The code is slicing strings at fixed byte indices (e.g., byte 120) without checking UTF-8 character boundaries. Chinese characters use 3 bytes each, so slicing in the middle causes the panic.

Suggested fix

Use char_indices() or check is_char_boundary() before slicing strings to properly handle multi-byte UTF-8 characters.