Unhandled rejection event in web streams when stream error is piped

### Version 21.1.0 ### Platform Linux kunigunde 6.5.9-arch2-1 #1 SMP PREEMPT_DYNAMIC Thu, 26 Oct 2023 00:52:20 +0000 x86_64 GNU/Linux ### Subsystem streams/web ### What steps will reproduce the bug? Run the following code: ```javascript import { ReadableStream } from "stream/web"; process.on('unhandledRejection', (err) => { console.log(`Unhandled rejection: ${err.message}`); }); const stream1 = new ReadableStream({ start(controller) { controller.error(new Error('Test')); }, }); const stream2 = new TransformStream(); stream1.pipeTo(stream2.writable); try { await stream2.readable.getReader().read(); } catch (err) { console.log(`Caught error: ${err.message}`); } ``` ### How often does it reproduce? Is there a required condition? With the given code example, it happens every time. It does _not_ happen in the following situations: * Reading from `stream1` directly rather than piping it to `stream2` * Reading from `stream2` but not `catch`ing the error but letting the app crash instead ### What is the expected behavior? Why is that the expected behavior? No `unhandledRejection` event should be triggered, since the exception is actually handled. ### What do you see instead? An `unhandledRejection` event is triggered. The output of the sample script is: ``` Caught error: Test Unhandled rejection: Test ``` ### Workaround I’m not sure if this has any unintended side effects, but catching the rejection by the promise returned by `pipeTo()` seems to solve the problem: ```javascript stream1.pipeTo(stream2.writable).catch(() => {}); ```