Using the MockAgent and the pipeline method

Bug Description

Pipeline mock fails when node:stream/promise pipeline is used.

Reproducible By

The first test passes. For the second test, the await pipeline(...) fails. The error is not catched.

// Import Node.js Dependencies
import { describe, it, afterEach } from "node:test";
import { pipeline } from "node:stream/promises";
import stream, { PassThrough, Readable } from "node:stream";
import assert from "node:assert";
import timers from "node:timers/promises";

// Import Third-Party Dependencies
import undici, { MockAgent } from "undici";

describe("undici.pipeline", async() => {
  let kMockAgent: MockAgent;

  afterEach(async() => {
    await kMockAgent.close();
  });

  it("OK : stream.pipeline", async() => {
    kMockAgent = new MockAgent();
    kMockAgent.disableNetConnect();
    undici.setGlobalDispatcher(kMockAgent);

    kMockAgent
      .get("https://boz.com")
      .intercept({ method: "POST", path: "/" })
      .reply(200, "Bar");

    const readable = Readable.from("Some text.".repeat(10_000));
    const request = undici.pipeline(
      "https://boz.com",
      { method: "POST" },
      ({ body }) => body
    );

    stream.pipeline(readable, request, new PassThrough(), () => void 0);
    await timers.setTimeout(100);

    assert.ok(1);
  });

  it("KO : stream/promises.pipeline", async() => {
    kMockAgent = new MockAgent();
    kMockAgent.disableNetConnect();
    undici.setGlobalDispatcher(kMockAgent);

    kMockAgent
      .get("https://boz.com")
      .intercept({ method: "POST", path: "/" })
      .reply(200, "Bar");

    const readable = Readable.from("Some text.".repeat(10_000));
    const request = undici.pipeline(
      "https://boz.com",
      { method: "POST" },
      ({ body }) => body
    );

    try {
      await pipeline(readable, request, new PassThrough());
    }
    catch (error) {
      console.error(error);
    }

    assert.ok(1);
  });
});

Expected Behavior

stream/promises.pipeline should work in the same way as stream/pipeline ?

Logs & Screenshots

Environment

Node 20.x
Undici 6.6.2

Start by running the provided Node 20 reproduction and compare undici.pipeline with node:stream/pipeline and node:stream/promises.pipeline. Inspect the pipeline and MockAgent behavior involved in the example, then add a regression test covering the promise-based pipeline. Done means the mocked request completes without an uncaught error and both pipeline forms behave consistently.