Basic checks

• I searched existing issues - this hasn't been reported
• I can reproduce this consistently
• This is a RubyLLM bug, not my application code

What's broken?

When using the Gemini-3-Pro-Preview model with RubyLLM and tools (function calling), the API returns an error about a missing thought_signature in functionCall parts. This prevents tool use with Gemini-3-Pro-Preview.

How to reproduce

• Configure RubyLLM with model = "gemini-3-pro-preview"
• Add a tool and call it via chat.
• Observe the error from the Gemini API.

Expected behavior

Tool calls should work with Gemini-3-Pro-Preview, and the required thought_signature should be included in the functionCall parts automatically.

What actually happened

The Gemini API returns:

RubyLLM::BadRequestError (Function call is missing a thought_signature in functionCall parts. This is required for tools to work correctly, and missing thought_signature may lead to degraded model performance. Additional data, Please refer to https://ai.google.dev/gemini-api/docs/thought-signatures for more details.)

Debug logs show the error occurs every time a tool is called.

Environment

• Ruby version: 3.3.6
• RubyLLM version: 1.9.1
• Provider: Gemini-3-Pro-Preview
• OS: macOS