Korean IME composition text appears below cursor position instead of at cursor

Bug Description

When typing Korean text in Claude Code CLI, the composing character (the character being typed with IME) appears on a separate line below the cursor position instead of at the actual cursor location.

Steps to Reproduce

1. Open Claude Code CLI in iTerm2
2. Switch to Korean input method (한글)
3. Start typing Korean text
4. Observe that the character being composed appears below the cursor line

Expected Behavior

The composing Korean character should appear at the cursor position, inline with the rest of the text.

Actual Behavior

The composing character renders on a line below the cursor position. Once the character is fully composed (e.g., by pressing space or continuing to the next syllable), it moves to the correct position.

Screenshot

<img width="350" height="239" alt="Image" src="https://github.com/user-attachments/assets/bc391fbd-4d0a-492c-a14a-c7764308008c" />

(The composing character "글" appears below the line where cursor is positioned after "한")

Environment

• Claude Code version: 2.1.23
• Terminal: iTerm2
• OS: macOS 15.6.1 (Build 24G90)
• Input Method: macOS Korean IME (2-Set Korean)

Additional Notes

• This issue does NOT occur in the regular iTerm2 shell - only within Claude Code CLI
• This suggests the issue is with Claude Code's terminal UI rendering, not iTerm2 itself