First workable server.

vendor/deno.land/std@0.191.0/streams/merge_readable_streams.ts

@@ -0,0 +1,42 @@
+// Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
+
+import { deferred } from "../async/deferred.ts";
+
+/**
+ * Merge multiple streams into a single one, not taking order into account.
+ * If a stream ends before other ones, the other will continue adding data,
+ * and the finished one will not add any more data.
+ */
+export function mergeReadableStreams<T>(
+  ...streams: ReadableStream<T>[]
+): ReadableStream<T> {
+  const resolvePromises = streams.map(() => deferred<void>());
+  return new ReadableStream<T>({
+    start(controller) {
+      let mustClose = false;
+      Promise.all(resolvePromises)
+        .then(() => {
+          controller.close();
+        })
+        .catch((error) => {
+          mustClose = true;
+          controller.error(error);
+        });
+      for (const [key, stream] of Object.entries(streams)) {
+        (async () => {
+          try {
+            for await (const data of stream) {
+              if (mustClose) {
+                break;
+              }
+              controller.enqueue(data);
+            }
+            resolvePromises[+key].resolve();
+          } catch (error) {
+            resolvePromises[+key].reject(error);
+          }
+        })();
+      }
+    },
+  });
+}