[BUG] MCP fails when reponse has unsupported image format

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 an MCP server returns tool results containing images with unsupported media types (e.g., image/svg+xml), Claude Code fails with a 400 API error. The Claude API only supports image/jpeg, image/png, image/gif, and image/webp, but Claude Code doesn't filter out unsupported formats from MCP tool responses.

Steps to Reproduce

1. Configure an MCP server that returns multiple image formats (e.g., mermaid-mcp, https://docs.mermaidchart.com/ai/mcp-server)
2. Call the tool: validate_and_render_mermaid_diagram
3. The response has a png and a svg, there is no way to skip the invalid format.
4. Claude errors, and it just replies with the error over and over again

What Should Happen?

I would expect, one of the following:

• The error to happen but have a way to ignore that value
• Claude identifying that there is a supported image and use it
• Claude providing a better messaging.

Error Messages/Logs

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.2.content.0.tool_result.content.2.image.source.base64.media_type: Input should be 'image/jpeg', 'image/png', 'image/gif' or 
     'image/webp'"},"request_id":"req_011CWd26zFQxj5Qjwj6psSAY"}

Steps to Reproduce

1. Configure an MCP server that returns multiple image formats (e.g., mermaid-mcp, https://docs.mermaidchart.com/ai/mcp-server)
2. Call the tool: validate_and_render_mermaid_diagram
3. The response has a png and a svg, there is no way to skip the invalid format.
4. Claude errors, and it just replies with the error over and over again

Example:
Prompt:

Validate this mermaid diagram
sequenceDiagram
    participant Customer
    participant Website
    participant "PaymentGateway" as PG
    participant Warehouse

    Customer->>Website: Browse products
    Customer->>Website: Place order
    Website->>Customer: Show order summary<br/>Request payment
    Website->>PG: Request payment authorization
    PG-->>Website: Payment status (approved/declined)
    alt Payment approved
        Website->>Warehouse: Send order details
        Warehouse-->>Website: Confirm order processing
        Website->>Customer: Order placed, confirmation sent
    else Payment declined
        Website->>Customer: Payment failed, request new method
    end 

Response:

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"messages.2.content.0.tool_result.content.2.image.source.base64.media_type: Input should be 'image/jpeg', 'image/png', 'image/gif' or 
     'image/webp'"},"request_id":"req_011CWd26zFQxj5Qjwj6psSAY"}

Claude Model

Opus

Is this a regression?

I don't know

Last Working Version

_No response_

Claude Code Version

2.0.76

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

I'm using kitty-terminal
Screen shot:

<img width="2242" height="1091" alt="Image" src="https://github.com/user-attachments/assets/fa2043f9-d7f8-4385-a886-f9a5d1358893" />