[BUG] Korean IME: Shift+Enter splits composed characters into separate lines on Windows

Bug Description

When typing Korean (Hangul) in Claude Code and pressing Shift+Enter to create a newline, the composed characters get split — each character drops to a separate line instead of inserting a single newline at the cursor position.

Example of what happens:

Instead of:

한글을 치다가 shift enter를 치면
이렇게 되어야 하는데

It becomes:

한
글
을
치
다
가

Each character gets separated onto its own line.

English input works fine — this only affects Korean (and likely other CJK IME) input.

Steps to Reproduce

1. Open Claude Code in VSCode integrated terminal on Windows
2. Type a Korean sentence (e.g. "한글을 입력하다가")
3. Press Shift+Enter while still in Korean input mode
4. Observe: characters split into separate lines

Expected Behavior

Shift+Enter should insert a single newline without breaking the composed Korean text.

Workaround

• Press Space (to finalize IME composition) before pressing Shift+Enter
• Or switch to English mode before pressing Shift+Enter

Environment Info

• Platform: Windows 11 (10.0.26100)
• Terminal: VSCode integrated terminal (bash shell)
• Claude Code version: latest
• Keyboard: Korean IME (Microsoft 한글 입력기)
• keybindings.json: Shift+Enter configured with \^[\r (via /terminal-setup)

Related Issues

• #5126 (Korean Text Input Rendering Breaks — closed)
• #2620 (IME Composition Failure for Korean Character Input)
• #19207 (IME cursor position support for CJK input)