fix(bun): polyfill ReadableStream to strip unsupported type direct

src/presets/bun/runtime/bun.ts

@@ -1,4 +1,36 @@
 import "#nitro/virtual/polyfills";
+
+// React 19's server.edge.js uses ReadableStream({ type: "direct", ... }), a
+// Cloudflare Workers extension. Bun follows the web spec strictly and throws
+// ERR_INVALID_ARG_VALUE for unknown `type` values. Strip it before it reaches
+// Bun's constructor so prerendering works without switching to the node preset.
+const _OriginalReadableStream = globalThis.ReadableStream;
+const _PatchedReadableStream = function ReadableStream(
+  underlyingSource?: UnderlyingDefaultSource | UnderlyingByteSource,
+  strategy?: QueuingStrategy,
+) {
+  if (
+    underlyingSource &&
+    (underlyingSource as Record<string, unknown>).type === "direct"
+  ) {
+    const { type: _type, ...rest } = underlyingSource as Record<string, unknown>;
+    return new _OriginalReadableStream(
+      rest as UnderlyingDefaultSource,
+      strategy,
+    );
+  }
+  return new _OriginalReadableStream(
+    underlyingSource as UnderlyingDefaultSource,
+    strategy,
+  );
+} as unknown as typeof ReadableStream;
+
+Object.setPrototypeOf(_PatchedReadableStream, _OriginalReadableStream);
+_PatchedReadableStream.prototype = _OriginalReadableStream.prototype;
+
+// @ts-expect-error -- intentional global override for compat
+globalThis.ReadableStream = _PatchedReadableStream;
+
 import type { ServerRequest } from "srvx";
 import { serve } from "srvx/bun";
 import wsAdapter from "crossws/adapters/bun";

test/fixture/server/routes/bun-direct-stream.ts

@@ -0,0 +1,15 @@
+export default () => {
+  const encoder = new TextEncoder();
+  const stream = new ReadableStream({
+    // @ts-expect-error - direct is a Cloudflare extension
+    type: "direct",
+    start(controller) {
+      controller.enqueue(encoder.encode("bun-direct"));
+      controller.close();
+    },
+  });
+
+  return {
+    isStream: stream instanceof ReadableStream,
+  };
+};

test/presets/bun.test.ts

@@ -1,7 +1,7 @@
 import { execa, execaCommandSync } from "execa";
 import { getRandomPort, waitForPort } from "get-port-please";
 import { resolve } from "pathe";
-import { describe } from "vitest";
+import { describe, it, expect } from "vitest";
 import { setupTest, testNitro } from "../tests.ts";
 
 const hasBun = execaCommandSync("bun --version", { stdio: "ignore", reject: false }).exitCode === 0;
@@ -25,5 +25,10 @@ describe.runIf(hasBun)("nitro:preset:bun", async () => {
       const res = await ctx.fetch(url, opts);
       return res;
     };
+  }, (ctx, callHandler) => {
+    it("bun: ReadableStream polyfill works", async () => {
+      const { data } = await callHandler({ url: "/bun-direct-stream" });
+      expect(data.isStream).toBe(true);
+    });
   });
 });