[BUG] Panic when handling Korean (UTF-8) characters in file/folder names

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 panics when processing HTML files containing Korean text. The Rust code attempts to
slice a UTF-8 string at a byte index that falls in the middle of a multi-byte Korean character.

Error Message:
thread '' panicked at
/rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb\library\core\src\str\mod.rs:833:21:
byte index 12 is not a char boundary; it is inside '드' (bytes 10..13) of 수 가이드
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace

The string 수 가이드 is part of 필수 가이드 (Korean text meaning "essential guide"). The
panic occurs because byte index 12 falls inside the character '드' which occupies bytes 10-13.

What Should Happen?

Claude Code should correctly handle UTF-8 multi-byte characters (Korean, Chinese, Japanese,
etc.) in file contents without panicking. String slicing should use character boundaries, not
raw byte indices.

Error Messages/Logs

thread '<unnamed>' panicked at 
  /rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb\library\core\src\str\mod.rs:833:21:
  byte index 12 is not a char boundary; it is inside '드' (bytes 10..13) of `수 가이드`
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Steps to Reproduce

1. Create an HTML file with Korean text in meta tags:

```html
<meta name="description" content="필수 가이드">

1. Run Claude Code in the project directory
2. Perform any operation that causes Claude Code to process/read the HTML file
3. Panic occurs during string processing

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.4

Platform

Other

Operating System

Windows

Terminal/Shell

Terminal.app (macOS)

Additional Information

Root Cause Analysis:
Korean characters use 3 bytes each in UTF-8 encoding. The code appears to use byte indexing
instead of character-aware indexing when slicing strings, which causes a panic when the index
falls in the middle of a multi-byte character.

Affected text: 필수 가이드 (in HTML meta description tag)

• '필' = bytes 0-2
• '수' = bytes 3-5
• ' ' = byte 6
• '가' = bytes 7-9
• '이' = bytes 10-12
• '드' = bytes 13-15

Byte index 12 is inside '이', not '드' as shown in error - the error message itself may be
truncating the string incorrectly.