fix(ext/node): yield to I/O in http2 write path so stream pipeline finishes (#33541)

Enables `test-stream-pipeline-http2` in node_compat suite.

---------

Signed-off-by: Divy Srivastava <dj.srivastava23@gmail.com>
Co-authored-by: divybot <divybot@users.noreply.github.com>
Co-authored-by: Divy Srivastava <me@littledivy.com>
Co-authored-by: Divy Srivastava <dj.srivastava23@gmail.com>

Author: divybot

ext/node/polyfills/http2.ts

@@ -1738,8 +1738,19 @@ class Http2Stream extends Duplex {
       done();
     };
     // Shutdown write stream right after last chunk is sent
-    // so final DATA frame can include END_STREAM flag
-    process.nextTick(() => {
+    // so final DATA frame can include END_STREAM flag.
+    //
+    // We diverge from Node here: upstream uses process.nextTick. Node can get
+    // away with that because their writeGeneric callback fires asynchronously
+    // via libuv I/O completion, so each write yields to the event loop. In
+    // our polyfill, the http2 handle's writev pushes data straight into
+    // nghttp2's send buffer and afterWriteDispatched invokes the write
+    // callback synchronously, so a Readable.pipe(req) loop becomes a tight
+    // sync-write -> nextTick -> sync-write chain that never yields. Once the
+    // peer's flow-control window fills, the inbound WINDOW_UPDATE never gets
+    // read and the pipeline deadlocks. setImmediate forces a check-phase
+    // boundary between write batches so I/O can run.
+    setImmediate(() => {
       if (
         writeCallbackErr ||
         !this._writableState.ending ||

tests/node_compat/config.jsonc

@@ -2671,6 +2671,7 @@
     "parallel/test-stream-pipe-without-listenerCount.js": {},
     "parallel/test-stream-pipeline-async-iterator.js": {},
     "parallel/test-stream-pipeline-duplex.js": {},
+    "parallel/test-stream-pipeline-http2.js": {},
     "parallel/test-stream-pipeline-listeners.js": {},
     "parallel/test-stream-pipeline-queued-end-in-destroy.js": {},
     "parallel/test-stream-pipeline-uncaught.js": {},