Unified provider sends `max_tokens` to OpenAI reasoning models

[n1ckoates]

ai-gateway-provider’s Unified route currently creates its models via @ai-sdk/openai-compatible:

const unified = createUnified();
const model = aigateway(unified('openai/o1-mini'));

When used with AI SDK’s standardized maxOutputTokens, the outgoing Chat Completions request contains:

{
  "model": "openai/o1-mini",
  "max_tokens": 1000
}

OpenAI reasoning models reject this field and require max_completion_tokens instead:

Unsupported parameter: 'max_tokens' is not supported with this model.
Use 'max_completion_tokens' instead.

The native Cloudflare OpenAI adapter does not have the issue:

const openai = createOpenAI();
const model = aigateway(openai.chat('o1-mini'));

That route uses @ai-sdk/openai, which performs the correct OpenAI-specific parameter mapping.

Suggested fix: have createUnified() supply transformRequestBody to its createOpenAICompatible instance. When Cloudflare’s model-capability metadata identifies an OpenAI reasoning model, move max_tokens to max_completion_tokens.