Custom LLM client fails on act

[Dor256]

I defined a custom LLM client and passed it to stagehand like so:

export class MyAiGatewayClient extends LLMClient {
  constructor(private model: Model) {
    super(model);    
  }
  
  async createChatCompletion<T>({ options }: CreateChatCompletionOptions): Promise<T> {
    invariant(options.response_model, "No response model");

    const request = {
      prompt: {
        openAiChatCompletionRequest: {
          model: this.model,
          messages: options.messages.map(this.toGatewayMessage),
          responseFormat: {
            type: "json_schema",
            schema: {
              name: options.response_model.name,
              schema: zodToJsonSchema(options.response_model.schema as any)
            }
          }
        }
      },
    };

    const response = await myLLMClient.request(request);

    const chatCompletionResponse = response.response?.openAiChatCompletionResponse;
    invariant(chatCompletionResponse, "No chat completion response");

    const { choices, object, model } = chatCompletionResponse;
    invariant(choices, "No choices");

    const parsedContent = JSON.parse(choices[0]?.message?.content
    return {
      data: parsedContent
    } as T;
  }
}

Everything works perfectly until the model decides to use act (e.g. click, scroll, whatever) and then I get an error with

/Users/dorb/Workspace/test/node_modules/@browserbasehq/stagehand/dist/index.js:22008
            throw new StagehandMissingArgumentError(
                  ^

StagehandMissingArgumentError: MissingArgumentError: No arguments provided to `act()`. Please ensure that all required arguments are passed in.
    at StagehandOperatorHandler.<anonymous> (test/node_modules/@browserbasehq/stagehand/dist/index.js:22008:19)
    at Generator.next (<anonymous>)
    at test/node_modules/@browserbasehq/stagehand/dist/index.js:79:61
    at new Promise (<anonymous>)
    at __async (test/node_modules/@browserbasehq/stagehand/dist/index.js:63:10)
    at StagehandOperatorHandler.executeAction (test/node_modules/@browserbasehq/stagehand/dist/index.js:21999:12)
    at StagehandOperatorHandler.<anonymous> (test/node_modules/@browserbasehq/stagehand/dist/index.js:21936:20)
    at Generator.next (<anonymous>)
    at fulfilled (test/node_modules/@browserbasehq/stagehand/dist/index.js:66:24)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

When I dug deeper into the code it looks like this line
Is not yielding anything and playwrightArguments is undefined.
Am I doing something wrong?