[Flight] Ensure we dedupe references if we later discover that it's the model root (#33666)

I noticed we weren't deduping these cases.

Author: sebmarkbage

packages/react-server-dom-webpack/src/__tests__/ReactFlightDOMBrowser-test.js

@@ -2574,4 +2574,54 @@ describe('ReactFlightDOMBrowser', () => {
     expect(errors).toEqual([new Error('Connection closed.')]);
     expect(container.innerHTML).toBe('');
   });
+
+  it('can dedupe references inside promises', async () => {
+    const foo = {};
+    const bar = {
+      foo: foo,
+    };
+    foo.bar = bar;
+
+    const object = {
+      foo: Promise.resolve(foo),
+      bar: Promise.resolve(bar),
+    };
+
+    const stream = await serverAct(() =>
+      ReactServerDOMServer.renderToReadableStream(object, webpackMap),
+    );
+
+    const response = await ReactServerDOMClient.createFromReadableStream(
+      passThrough(stream),
+    );
+
+    const responseFoo = await response.foo;
+    const responseBar = await response.bar;
+    expect(responseFoo.bar).toBe(responseBar);
+    expect(responseBar.foo).toBe(responseFoo);
+  });
+
+  it('can deduped outlined references inside promises', async () => {
+    const foo = {};
+    const bar = new Set([foo]); // This will be outlined which can create a future reference
+    foo.bar = bar;
+
+    const object = {
+      foo: Promise.resolve(foo),
+      bar: Promise.resolve(bar),
+    };
+
+    const stream = await serverAct(() =>
+      ReactServerDOMServer.renderToReadableStream(object, webpackMap),
+    );
+
+    const response = await ReactServerDOMClient.createFromReadableStream(
+      passThrough(stream),
+    );
+
+    const responseFoo = await response.foo;
+    const responseBar = await response.bar;
+    expect(responseFoo.bar).toBe(responseBar);
+    expect(Array.from(responseBar)[0]).toBe(responseFoo);
+  });
 });

packages/react-server/src/ReactFlightServer.js

@@ -3220,6 +3220,11 @@ function renderModelDestructive(
 
     if (existingReference !== undefined) {
       if (modelRoot === value) {
+        if (existingReference !== serializeByValueID(task.id)) {
+          // Turns out that we already have this root at a different reference.
+          // Use that after all.
+          return existingReference;
+        }
         // This is the ID we're currently emitting so we need to write it
         // once but if we discover it again, we refer to it by id.
         modelRoot = null;