stream: pipeTo treats writer transform() method as pipeline transform

[trivikr]

Version

26.2.0

Platform

macOS 26.5.0

Subsystem

stream

What steps will reproduce the bug?

import { pipeTo, from } from 'node:stream/iter';

const chunks = [];

const writer = {
  transform() {
    console.log('BUG: writer.transform() was called');
    return null;
  },
  write(chunk) {
    chunks.push(new TextDecoder().decode(chunk));
  },
};

await pipeTo(from('hello'), writer);

console.log(chunks.join(''));

How often does it reproduce? Is there a required condition?

Always

What is the expected behavior? Why is that the expected behavior?

hello

The final pipeTo() argument should be treated only as the destination writer; transform objects are only the arguments before the writer.

What do you see instead?

BUG: writer.transform() was called
node:internal/streams/iter/pull:584
  for await (const item of output) {
                           ^

TypeError: Cannot read properties of null (reading 'Symbol(Symbol.asyncIterator)')
    at applyStatefulAsyncTransform (node:internal/streams/iter/pull:584:28)
    at applyStatefulAsyncTransform.next (<anonymous>)
    at createAsyncPipeline (node:internal/streams/iter/pull:703:22)
    at createAsyncPipeline.next (<anonymous>)
    at pipeTo (node:internal/streams/iter/pull:1000:26)
    at file:///Users/trivikram/workspace/test-repro/repro.js:15:7
    at ModuleJob.run (node:internal/modules/esm/module_job:439:25)
    at process.processTicksAndRejections (node:internal/process/task_queues:104:5)
    at async node:internal/modules/esm/loader:646:26
    at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:101:5)

pipeTo() calls writer.transform() when the destination writer object also has a transform() method, so the writer is treated as a transform as well as the destination.

Additional information

No response