gemini-cli - 💡(How to fix) Fix BUG FIGMA MCP HTTP 400: Image MIME type mismatch, WebP images incorrectly labeled as image/png in tool_result payloads [1 pull requests]

What happened?

When using Antigravity Desktop (Version 2.0.11) with the official Figma MCP integration, tool results containing images occasionally fail with an HTTP 400 error.

The API reports that an image was declared as image/png, but the actual image data is WebP:

messages.48.content.0.tool_result.content.1.image.source.base64: The image was specified using the image/png media type, but the image appears to be a image/webp image

Trace ID: 0xb7ecf751f1ab1d77 Request ID: req_vrtx_011CbpH8KZBfF4SscpfGt5U1

The issue has occurred repeatedly across multiple conversations and agent runs and causes the session to fail.

What did you expect to happen?

The platform should correctly detect the actual image format and send the correct MIME type, or convert the image to the declared format before sending it to the model API.

The conversation should continue without the request being rejected.

Client information

Run gemini to enter the interactive CLI, then run the /about command.

> /about
│ About Gemini CLI                                                                                                     │
│                                                                                                                      │
│ CLI Version                              0.45.2                                                                      │
│ Git Commit                               dfa8394ca                                                                   │
│ Model                                    Auto                                                                        │
│ Sandbox                                  no sandbox                                                                  │
│ OS                                       win32                                                                       │
│ Auth Method                              Signed in with Google (REDACTED)                                │
│ Tier                                     Gemini Code Assist in Google One AI Pro

Login information

Google Account

Using Antigravity Desktop with the official Figma MCP server.

Anything else we need to know?

Platform: Windows

The issue appears when processing Figma content through the official Figma MCP integration.

No custom MCP code or middleware is being used.

The error appears to indicate that a WebP image is being packaged as image/png before being sent to the model API.

Trajectory ID: 694421d2-c3df-4a81-a365-0503ffa7c7d1

Trace ID: 0xb7ecf751f1ab1d77