stream/iter: push writer.end() resolves before readable drains buffered data

[trivikr]

Version

26.2.0

Platform

macOS 26.5.0

Subsystem

stream

What steps will reproduce the bug?

import { push } from 'node:stream/iter';

const { writer, readable } = push();
writer.writeSync('hello');
const events = [];

writer.end().then(() => {
  events.push('end resolved');
});

await Promise.resolve();

events.push('after microtask');
for await (const _ of readable) {
  events.push('readable drained');
}
console.log(events);

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

Always

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

[ 'after microtask', 'readable drained', 'end resolved' ]

writer.end() should stay pending until the readable drains, so end resolved should appear after readable drained.

What do you see instead?

[ 'end resolved', 'after microtask', 'readable drained' ]

writer.end() currently resolves before the readable side consumes the buffered "hello" chunk

Additional information

No response