agent.generate() result does not contain reasoning.

import { openai } from "@ai-sdk/openai";
import { Agent } from "@mastra/core/agent";
import { describe, expect, it } from "vitest";

const reasoningAgent = new Agent({
  name: 'reasoningAgent',
  instructions: `You are a reasoning agent. Think very carefully about the problem you are given and come up with the best solution.`,
  model: openai('gpt-5'),
});

describe('reasoning tests', () => {
  it('should provide reasoning text', async () => {
    const result = await reasoningAgent.generate(
      [
        {
         role: 'user',
         content: 'If John has 2 apples and Jane has 3 apples, then John gives one apple to Jane, how many apples does John have left?',
        }
      ],
      {
        providerOptions:
        {
          openai:
          {
            reasoningEffort: 'high',
          },
        },
      },
    );
    expect(result.text.length).toBeGreaterThan(0);
    expect(result.reasoningText).toBeDefined();
    expect(result.reasoningText?.length).toBeGreaterThan(0);
  });
});