[Bug] UTF-8 string indexing panic with multi-byte characters (Korean text)

Bug Description
thread '<unnamed>' (5207549) panicked at /rustc/ed61e7d7e242494fb7057f2657300d9e77bb4fcb/library/core/src/str/mod.rs:833:21:
byte index 12 is not a char boundary; it is inside '원' (bytes 10..13) of 7.5천만원 이하 조건이 적용됩니다."
note: run with RUST_BACKTRACE=1 environment variable to display a backtrace
fatal runtime error: failed to initiate panic, error 5, aborting
[1] 93879 abort claude --dangerously-skip-permissions

I can see that Claude Code crashed with a string indexing error while processing Korean text. This is a bug in the CLI itself - it tried to split a multi-byte UTF-8 character (한글) at an invalid byte boundary.

Environment Info

• Platform: darwin
• Terminal: iTerm.app
• Version: 2.0.76
• Feedback ID: 3f177102-07b5-463d-b7b4-45dc9a77c66f

Errors

[{"error":"Error: NON-FATAL: Lock acquisition failed for /Users/haseongpark/.local/share/claude/versions/2.0.76 (expected in multi-process scenarios)\n    at XZR (/$bunfs/root/claude:2430:2165)\n    at fUA (/$bunfs/root/claude:2430:1885)\n    at processTicksAndRejections (native:7:39)","timestamp":"2026-01-04T01:10:40.223Z"},{"error":"AbortError: The operation was aborted.\n    at unknown\n    at abortChildProcess (node:child_process:935:42)\n    at onAbortListener2 (node:child_process:35:24)\n    at abort (unknown)\n    at <anonymous> (/$bunfs/root/claude:4923:14420)","timestamp":"2026-01-04T01:10:42.540Z"}]