From d1d10f3c7a57f87d0533c579f9ddc24cf33be8ad Mon Sep 17 00:00:00 2001
From: Maxim <maxim.zubarev@icloud.com>
Date: Sun, 1 Nov 2026 02:45:34 +0100
Subject: [PATCH] fix(react): render streamed repeat items before completion

---
 packages/react/src/chat-streaming.test.tsx | 131 +++++++++++++++++++++
 packages/react/src/hooks.ts                |  26 ++--
 2 files changed, 142 insertions(+), 15 deletions(-)
 create mode 100644 packages/react/src/chat-streaming.test.tsx

diff --git a/packages/react/src/chat-streaming.test.tsx b/packages/react/src/chat-streaming.test.tsx
new file mode 100644
index 00000000..b73c9d5e
--- /dev/null
+++ b/packages/react/src/chat-streaming.test.tsx
@@ -0,0 +1,131 @@
+import React from "react";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { act, cleanup, render, screen, waitFor } from "@testing-library/react";
+import type { JsonPatch, Spec } from "@json-render/core";
+import { useChatUI } from "./hooks";
+import { JSONUIProvider, Renderer, type ComponentRegistry } from "./renderer";
+
+afterEach(() => {
+  cleanup();
+  vi.unstubAllGlobals();
+});
+
+const registry: ComponentRegistry = {
+  List: ({ children }) => <ul>{children}</ul>,
+  Item: ({ element }) => <li>{String(element.props.label)}</li>,
+};
+
+describe("useChatUI streamed state", () => {
+  it("renders appended, edited, and removed repeat items before the stream ends", async () => {
+    let controller!: ReadableStreamDefaultController<Uint8Array>;
+    const stream = new ReadableStream<Uint8Array>({
+      start(value) {
+        controller = value;
+      },
+    });
+    vi.stubGlobal(
+      "fetch",
+      vi.fn(async () => new Response(stream)),
+    );
+
+    let chat!: ReturnType<typeof useChatUI>;
+    const onComplete = vi.fn();
+    function App() {
+      chat = useChatUI({ api: "/api/chat", onComplete });
+      const spec = chat.messages.at(-1)?.spec;
+      return (
+        <JSONUIProvider registry={registry} initialState={spec?.state}>
+          <Renderer
+            spec={spec ?? null}
+            registry={registry}
+            loading={chat.isStreaming}
+          />
+        </JSONUIProvider>
+      );
+    }
+    render(<App />);
+
+    let request!: Promise<void>;
+    await act(async () => {
+      request = chat.send("Show the items");
+    });
+
+    async function push(...patches: JsonPatch[]) {
+      await act(async () => {
+        controller.enqueue(
+          new TextEncoder().encode(
+            patches.map((patch) => JSON.stringify(patch)).join("\n") + "\n",
+          ),
+        );
+      });
+    }
+
+    const labels = () =>
+      screen.queryAllByRole("listitem").map((item) => item.textContent);
+    const currentSpec = () => chat.messages.at(-1)!.spec as Spec;
+
+    try {
+      await push(
+        { op: "add", path: "/root", value: "list" },
+        {
+          op: "add",
+          path: "/elements/list",
+          value: {
+            type: "List",
+            props: {},
+            repeat: { statePath: "/items", key: "id" },
+            children: ["item"],
+          },
+        },
+        {
+          op: "add",
+          path: "/elements/item",
+          value: { type: "Item", props: { label: { $item: "label" } } },
+        },
+        { op: "add", path: "/state", value: { items: [] } },
+      );
+      const empty = currentSpec();
+      expect(labels()).toEqual([]);
+
+      await push({
+        op: "add",
+        path: "/state/items/0",
+        value: { id: "a", label: "First" },
+      });
+      await waitFor(() => expect(labels()).toEqual(["First"]));
+      const first = currentSpec();
+      expect(empty.state?.items).toEqual([]);
+      expect(chat.isStreaming).toBe(true);
+
+      await push({
+        op: "add",
+        path: "/state/items/-",
+        value: { id: "b", label: "Second" },
+      });
+      await waitFor(() => expect(labels()).toEqual(["First", "Second"]));
+
+      await push({
+        op: "replace",
+        path: "/state/items/0/label",
+        value: "Updated",
+      });
+      await waitFor(() => expect(labels()).toEqual(["Updated", "Second"]));
+
+      await push({ op: "remove", path: "/state/items/1" });
+      await waitFor(() => expect(labels()).toEqual(["Updated"]));
+      expect(first.state?.items).toEqual([{ id: "a", label: "First" }]);
+      expect(chat.isStreaming).toBe(true);
+      expect(onComplete).not.toHaveBeenCalled();
+    } finally {
+      await act(async () => {
+        controller.close();
+        await request;
+      });
+    }
+
+    expect(chat.error).toBeNull();
+    expect(chat.isStreaming).toBe(false);
+    expect(onComplete).toHaveBeenCalledOnce();
+    expect(onComplete.mock.calls[0]![0].spec).toEqual(currentSpec());
+  });
+});
diff --git a/packages/react/src/hooks.ts b/packages/react/src/hooks.ts
index e222d501..a898e2b1 100644
--- a/packages/react/src/hooks.ts
+++ b/packages/react/src/hooks.ts
@@ -832,21 +832,17 @@ export function useChatUI({
           onPatch(patch) {
             hasSpec = true;
             applySpecPatch(currentSpec, patch);
+            // Detach state from the mutable accumulator so later patches cannot
+            // mutate published arrays without notifying StateProvider.
+            const spec: Spec = {
+              root: currentSpec.root,
+              elements: { ...currentSpec.elements },
+              ...(currentSpec.state
+                ? { state: structuredClone(currentSpec.state) }
+                : {}),
+            };
             setMessages((prev) =>
-              prev.map((m) =>
-                m.id === assistantId
-                  ? {
-                      ...m,
-                      spec: {
-                        root: currentSpec.root,
-                        elements: { ...currentSpec.elements },
-                        ...(currentSpec.state
-                          ? { state: { ...currentSpec.state } }
-                          : {}),
-                      },
-                    }
-                  : m,
-              ),
+              prev.map((m) => (m.id === assistantId ? { ...m, spec } : m)),
             );
           },
           onText(line) {
@@ -876,7 +872,7 @@ export function useChatUI({
                 root: currentSpec.root,
                 elements: { ...currentSpec.elements },
                 ...(currentSpec.state
-                  ? { state: { ...currentSpec.state } }
+                  ? { state: structuredClone(currentSpec.state) }
                   : {}),
               }
             : null,