fix issue with tool calling using gemini 3.0 pro perview

[lukemilby]

issue where gemini 3.0 pro preview would error because google's thought_signature was missing

response I would get

Error processing message: LLM call failed after retries: API request failed:
  Status: 400
  Body:   [{
  "error": {
    "code": 400,
    "message": "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, function call default_api:read_file , position 20. Please refer to https://ai.google.dev/gemini-api/docs/thought-signatures for more details.",
    "status": "INVALID_ARGUMENT"
  }
}

[Leeaandrob]

@Zepan Fixes tool calling with Gemini 3.0 Pro Preview. Gemini is a popular provider and tool calling is a core feature.

Recommendation: Merge. +47/-16, targeted fix for a widely-used provider.