doc: clarify mutable Web Stream chunk reuse

Document when a mutable chunk can be reused after writer.write()
fulfills, and prohibit mutation while the write is pending.

Explain copying in byte mode, reference passing in object mode, and
preservation of bytes retained by a Duplex readable side.

Signed-off-by: seungwoo <zoozoo1302@gmail.com>

Author: seungwoo505

doc/api/stream.md

@@ -3339,6 +3339,14 @@ changes:
 * `streamWritable` {stream.Writable}
 * Returns: {WritableStream}
 
+For streams not operating in object mode, a mutable {Buffer}, {TypedArray},
+{DataView}, {ArrayBuffer}, or {SharedArrayBuffer} passed to the returned stream's
+writer can be reused after the promise returned by `writer.write()` is
+fulfilled. Do not modify the chunk or its underlying bytes while that promise
+is pending. The adapter may copy the chunk, so the underlying Node.js stream is
+not guaranteed to receive the same object. Chunks written to streams operating
+in object mode are passed by reference without copying.
+
 ### `stream.Duplex.from(src)`
 
 <!-- YAML
@@ -3507,6 +3515,12 @@ changes:
   * `readable` {ReadableStream}
   * `writable` {WritableStream}
 
+The `writable` stream has the same mutable chunk reuse behavior as
+[`stream.Writable.toWeb()`][]. For streams not operating in writable object mode,
+reusing the chunk after `writer.write()` is fulfilled does not modify bytes
+retained by the Node.js stream's readable side. The adapter may copy chunks
+before passing them to the Node.js stream.
+
 ```mjs
 import { Duplex } from 'node:stream';
 
@@ -5088,6 +5102,7 @@ contain multi-byte characters.
 [`readable.push('')`]: #readablepush
 [`readable.setEncoding()`]: #readablesetencodingencoding
 [`stream.Readable.from()`]: #streamreadablefromiterable-options
+[`stream.Writable.toWeb()`]: #streamwritabletowebstreamwritable
 [`stream.addAbortSignal()`]: #streamaddabortsignalsignal-stream
 [`stream.compose(...streams)`]: #streamcomposestreams
 [`stream.cork()`]: #writablecork