stream: fix pipeTo to defer writes per WHATWG spec

The WHATWG Streams spec requires that pipeTo's chunk handling must
queue a microtask before calling the write algorithm. This ensures
that enqueue() does not synchronously trigger writes.

Previously, PipeToReadableStreamReadRequest[kChunk] would synchronously
call writableStreamDefaultWriterWrite(), which violated the spec and
caused the WPT test "enqueue() must not synchronously call write
algorithm" to fail.

Fix by wrapping the write operation in queueMicrotask(), which defers
it to the next microtask as required by the spec.

Refs: whatwg/streams#1243

Author: mcollina

lib/internal/webstreams/readablestream.js

@@ -1584,9 +1584,14 @@ class PipeToReadableStreamReadRequest {
   }
 
   [kChunk](chunk) {
-    this.state.currentWrite = writableStreamDefaultWriterWrite(this.writer, chunk);
-    setPromiseHandled(this.state.currentWrite);
-    this.promise.resolve(false);
+    // Per spec, pipeTo must queue a microtask for the write to avoid
+    // synchronous write during enqueue(). See WHATWG Streams spec
+    // "ReadableStreamPipeTo" step 15's "chunk steps".
+    queueMicrotask(() => {
+      this.state.currentWrite = writableStreamDefaultWriterWrite(this.writer, chunk);
+      setPromiseHandled(this.state.currentWrite);
+      this.promise.resolve(false);
+    });
   }
 
   [kClose]() {

test/wpt/status/streams.json

@@ -2,14 +2,6 @@
   "idlharness-shadowrealm.window.js": {
     "skip": "ShadowRealm support is not enabled"
   },
-  "piping/general-addition.any.js": {
-    "fail": {
-      "note": "Blocked on https://github.com/whatwg/streams/issues/1243",
-      "expected": [
-        "enqueue() must not synchronously call write algorithm"
-      ]
-    }
-  },
   "queuing-strategies-size-function-per-global.window.js": {
     "skip": "Browser-specific test"
   },