[BUG] MCP: structuredContent overrides content field, losing actual tool response

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?

Claude Code seems to be unable to properly read MCP responses that contain both structuredContent and content data.

This has been reported numerous times already (#45575, #59480). This is a significant issue for me so I really am hoping to get more eyes on this one, since the others seem to have gotten lost.

I am experiencing this issue with the Roblox Studio MCP, where Claude is unable to see the full response from certain tools such as inspect_instance (I confirmed that those tools do actually return more data than Claude seems to be able to see)

What Should Happen?

Claude should be able to read both fields if supplied.

Error Messages/Logs

Steps to Reproduce

1. Make/Run any MCP server that has tools that contain both fields in their responses (Roblox Studio MCP inspect_instance is a concrete example of this)
2. Have Claude run the command and tell you what it sees
3. Notice that the response Claude sees is significantly lacking in information despite the MCP being configured to deliver more

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.1.159 (Claude Code)

Platform

Anthropic API

Operating System

Windows

Terminal/Shell

VS Code integrated terminal

Additional Information

_No response_