Panic when --continue with Japanese text in todo/history

## Description
Claude Code crashes with a Rust panic when using
--continue flag with Japanese text in the conversation
history or todo list.

## Error
thread '' (1409884) panicked at /rustc/ed61e7d7e242494fb70
57f2657300d9e77bb4fcb/library/core/src/str/mod.rs:833:21:
byte index 26 is not a char boundary; it is inside '除'
(bytes 24..27) of と深夜トリガー削除 ✅ 2025-12-16
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 --continue

## Environment

• OS: macOS (Darwin 25.1.0)
• Claude Code version: latest

## Steps to Reproduce

1. Have a session with Japanese text in todo list (e.g.,

深夜トリガー削除 ✅ 2025-12-16)

1. Exit the session
2. Run claude --continue
3. Crash occurs

## Expected Behavior
Should handle UTF-8 multibyte characters correctly when
slicing strings.

## Root Cause (suspected)
The Rust code is slicing a string at a byte index that
falls in the middle of a multibyte UTF-8 character
(Japanese kanji '除' spans bytes 24-27, but the code tries
to slice at index 26).