[BUG] non-ASCII string parameters for remote MCP servers are converted to null

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?

The model is trying to use an http-based mcp tool and pass strings with non-ASCII chars. But the string is converted to null before it's passed on the the server. (I can see that because in Claude Caude the log line with the call to the mcp tool contains "calling MCP tool tool_name("param1": null, "param2": null).

Trying to isolate the bug, I found:

• ASCII chars and int params are passed correctly
• If the server is local (stdio), non-ASCII chars are passed correctly

So, the bug exists only when it's a remote server + non-ASCII strings.

What Should Happen?

Non-ASCII chars should be passed to remote MCP servers as the model intends, not as nulls.

Error Messages/Logs

Steps to Reproduce

1. Install a remote MCP server.
2. Ask the model to call an MCP tool and pass parameters in Cyrillic.

Claude Model

Other (MiniMax-M2.7)

Is this a regression?

No, this never worked

Last Working Version

_No response_

Claude Code Version

2.1.104

Platform

Other

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

_No response_