[BUG] `Write` and `Update` tools normalize unicode double quotes to standard ASCII double quote

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?

For some reason both Write and Update tools convert typographic unicode Quotes U+201C (“) and U+201D (”) to the standard double ASCI Quote U+0022 (").

This is particularly problematic when editing json files, as it corrupts them.

What Should Happen?

Preserve the correct unicode symbol.

Error Messages/Logs

Claude code Prompt:

>
1. create a test.txt file and use the Write tool to write the unicode symbol U+201C in it
2. then check the unicode contents of that file
3. if something is unusual, please explain 

⏺ Write(test.txt)
  ⎿  Wrote 1 lines to test.txt
     "

⏺ Bash(xxd /Users/janpaepke/dev/test.txt)
  ⎿  00000000: 22                                       "

⏺ Unusual finding: The file contains 0x22 (1 byte), which is the ASCII straight double quote " (U+0022).

  However, U+201C is the left double quotation mark " (curly quote), which in UTF-8 should be encoded as 3 bytes: E2 80 9C.

Steps to Reproduce

Use prompt above to reproduce.
It gets even more concerning, if you ask to make the file contents the unicode symbols U+201C and U+201D. This will be normalized to "" and result in an empty file. 😳

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.64

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_