google payloads with anthropic models don't work with tool calls

[knjiang]

the original payload for toolCallRequest with google is https://github.com/braintrustdata/lingua/blob/main/payloads/cases/simple.ts#L405C1-L432C7:

{
    google: {
      contents: [
        {
          role: "user",
          parts: [{ text: "What's the weather like in San Francisco?" }],
        },
      ],
      tools: [
        {
          functionDeclarations: [
            {
              name: "get_weather",
              description: "Get the current weather for a location",
              parameters: {
                type: Type.OBJECT,
                properties: {
                  location: {
                    type: Type.STRING,
                    description: "The city and state, e.g. San Francisco, CA",
                  },
                },
                required: ["location"],
              },
            },
          ],
        },
      ],
    },
}

example of the google payload -> transformed anthropic request that results in an API error from anthropic:

{
  "max_tokens": 4096,
  "messages": [
    {
      "content": "What's the weather like in San Francisco?",
      "role": "user",
    },
  ],
  "model": "claude-sonnet-4-5-20250929",
  "tools": [
    {
      "description": "Get the current weather for a location",
      "input_schema": {
        "properties": {
          "location": {
            "description": "The city and state, e.g. San Francisco, CA",
            "type": "string",
          },
        },
        "required": [
          "location",
        ],
        "type": "object",
      },
      "name": "get_weather",
    },
  ],
}

the anthropic response when we trying translating google payloads to anthropic by using an anthropic model -> https://github.com/braintrustdata/lingua/blob/main/payloads/transforms/google_to_anthropic/toolCallRequest.json

{
  "error": "400 {\"type\":\"error\",\"error\":{\"type\":\"invalid_request_error\",\"message\":\"tools.0.custom.input_schema.type: Input should be 'object'\"},\"request_id\":\"req_011CZbYt6Kw83ZmAdNZQzYZA\"}",
  "name": "Error"
}

this specific issue should cover the following cases from transform_errors.json:

  "google_to_anthropic": {
    "toolCallRequest": "Anthropic rejected: tool input_schema type must be 'object', not null",
    "toolChoiceRequiredParam": "Anthropic rejected: tool input_schema type must be 'object', not null",
    "toolChoiceAutoParam": "Anthropic rejected: tool input_schema type must be 'object', not null",
    "toolChoiceAnyParam": "Anthropic rejected: tool input_schema type must be 'object', not null",
    "toolChoiceNoneParam": "Anthropic rejected: tool input_schema type must be 'object', not null",
    "toolModeValidatedParam": "Anthropic rejected: tool input_schema type must be 'object', not null"
  },