[BUG] IME composition Enter key triggers submission on claude.ai/code (Chrome)

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?

On claude.ai/code (Claude Code Web), pressing the Enter key to confirm an IME (Input Method Editor) conversion unintentionally submits the message. This makes it nearly impossible to type Japanese text that requires kanji conversion.

This issue was previously fixed for the VS Code extension (#8405, closed Oct 2025) but is occurring on the Claude Code Web platform.

Steps to Reproduce

1. Open https://claude.ai/code in Google Chrome on macOS
2. Focus on the chat input field
3. Switch to Japanese IME
4. Type a phrase that requires conversion (e.g., type "nihongo" to get 「日本語」)
5. Press Enter to confirm the IME conversion candidate

Expected Behavior

The Enter key should only confirm the IME conversion. The message should not be submitted until the user presses Enter again after composition is complete.

Actual Behavior

The Enter key immediately submits the message with the partially composed text, before the user finishes typing their full message.

Related Issues

• #8405 — Same issue in VS Code extension (fixed)
• #30540 — Same issue in Claude Desktop Plan feedback (closed as duplicate of #8405)

Root Cause (likely)

The compositionstart / compositionend events are not being handled to suppress Enter key submission during active IME composition, similar to the original cause in #8405.

Environment

• Platform: claude.ai/code (Claude Code Web)
• Browser: Google Chrome
• OS: macOS