Empty function tool parameters cause 500 error with Anthropic provider

Type: Bug

Description

When a function tool is defined with empty parameters ("parameters": {}), the Responses API forwards it as-is to the inference provider. Anthropic's OpenAI-compatible endpoint rejects this because parameters.type is a required field, returning:

500 - tools.0.function.parameters.type: Field required

Similarly, if parameters contains properties but no type field, the request is also rejected.

Steps to Reproduce

1. Configure OGX with remote::anthropic provider
2. Create a response with a no-argument function tool:

client.responses.create(
    model="anthropic/claude-sonnet-4-6",
    input=[{"role": "user", "content": "what's the current time?"}],
    tools=[{
        "type": "function",
        "name": "get_current_time",
        "description": "Get the current time",
        "parameters": {},
    }],
)

3. Server returns 500

Verified Against Anthropic API