[BUG] Japanese characters in custom title cause malformed JSON, rename doesn't persist

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?

When I rename a conversation to a title containing Japanese characters (e.g. "ミカサ商事"), the rename appears to save but does not persist. After navigating to another conversation and returning, the title reverts to the auto-generated English AI title.

After investigating the JSONL file (~/.claude/projects/.../[session-id].jsonl), I found the root cause: the custom-title record is written with malformed JSON — the closing double-quote of the customTitle string value is missing, making the JSON unparseable.

Actual entry written:
{"type":"custom-title","sessionId":"...","customTitle":"ミカサ商事}

Expected entry:
{"type":"custom-title","sessionId":"...","customTitle":"ミカサ商事"}

Because the JSON cannot be parsed, the extension falls back to the ai-title entry (which contains the English auto-generated title), making the rename ineffective.

Environment: Windows 11, VS Code extension (entrypoint: claude-vscode), Claude Code v2.1.131

What Should Happen?

Renaming a conversation to a title containing Japanese (or other multibyte) characters should persist correctly. The custom-title entry in the JSONL file should be valid JSON with a properly terminated string value.

Error Messages/Logs

Steps to Reproduce

1. Open Claude Code in VS Code on Windows
2. Start a conversation in Japanese (e.g. ask something in Japanese)
3. In the conversation list sidebar, hover over the conversation and click the pencil (rename) icon
4. Type a Japanese title (e.g. "ミカサ商事") and press Enter
5. Navigate to a different conversation
6. Return to the renamed conversation
7. Observe that the title has reverted to the auto-generated English title

Claude Model

None

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.131

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_