stream: remove transform-writer handling in pipeTo

The pipeTo() and pipeToSync() argument parser already requires the
destination argument to be a writer. Remove the later transform-writer
handling so writer objects with a transform() method are treated only
as destinations.

Fixes: #63683

Signed-off-by: Kamat, Trivikram <16024985+trivikr@users.noreply.github.com>
Assisted-by: openai:gpt-5.5
PR-URL: #63684
Fixes: #63683
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>

Author: trivikr

lib/internal/streams/iter/pull.js

@@ -946,11 +946,6 @@ function pull(source, ...args) {
 function pipeToSync(source, ...args) {
   const { transforms, writer, options } = parsePipeToArgs(args, 'writeSync');
 
-  // Handle transform-writer
-  if (isTransformObject(writer)) {
-    ArrayPrototypePush(transforms, writer);
-  }
-
   // Normalize source and create pipeline
   const normalized = fromSync(source);
   const pipeline = transforms.length > 0 ?
@@ -1017,11 +1012,6 @@ async function pipeTo(source, ...args) {
     validateAbortSignal(options.signal, 'options.signal');
   }
 
-  // Handle transform-writer
-  if (isTransformObject(writer)) {
-    ArrayPrototypePush(transforms, writer);
-  }
-
   const signal = options?.signal;
 
   // Check for abort

test/parallel/test-stream-iter-pipeto.js

@@ -141,6 +141,31 @@ async function testPipeToSyncWithTransforms() {
   assert.strictEqual(chunks.join(''), 'HELLO');
 }
 
+async function testPipeToWriterTransformMethodIgnored() {
+  const chunks = [];
+  const writer = {
+    transform: common.mustNotCall(),
+    write(chunk) { chunks.push(new TextDecoder().decode(chunk)); },
+  };
+
+  await pipeTo(from('hello'), writer);
+  assert.strictEqual(chunks.join(''), 'hello');
+}
+
+async function testPipeToSyncWriterTransformMethodIgnored() {
+  const chunks = [];
+  const writer = {
+    transform: common.mustNotCall(),
+    writeSync(chunk) {
+      chunks.push(new TextDecoder().decode(chunk));
+      return true;
+    },
+  };
+
+  pipeToSync(fromSync('hello'), writer);
+  assert.strictEqual(chunks.join(''), 'hello');
+}
+
 // PipeTo with writev writer
 async function testPipeToWithWritevWriter() {
   const allChunks = [];
@@ -301,6 +326,8 @@ Promise.all([
   testPipeToWithSignal(),
   testPipeToWithTransforms(),
   testPipeToSyncWithTransforms(),
+  testPipeToWriterTransformMethodIgnored(),
+  testPipeToSyncWriterTransformMethodIgnored(),
   testPipeToWithWritevWriter(),
   testPipeToSyncFallback(),
   testPipeToPreventFail(),