test: cover stale conversation switching (#18211)

## Summary

Add focused frontend regression coverage for stale conversation messages
during chat session switching.

Related: #18140.

Replaces #18208.

web/src/pages/next-chats/chat/chat-box/single-chat-box.test.tsx

@@ -0,0 +1,123 @@
+import { render, waitFor } from '@testing-library/react';
+import React from 'react';
+
+import { MessageType } from '@/constants/chat';
+import { SingleChatBox } from './single-chat-box';
+
+const mockHydrateFromServer = jest.fn();
+const mockUseGetChatSearchParams = jest.fn();
+
+jest.mock('@/components/message-input/next', () => ({
+  NextMessageInput: () => null,
+}));
+jest.mock('@/components/message-item', () => () => null);
+jest.mock('@/components/pdf-drawer', () => () => null);
+jest.mock('@/components/pdf-drawer/hooks', () => ({
+  useClickDrawer: () => ({
+    visible: false,
+    hideModal: jest.fn(),
+    documentId: '',
+    selectedChunk: undefined,
+    clickDocumentButton: jest.fn(),
+  }),
+}));
+jest.mock('@/hooks/use-chat-request', () => ({
+  useFetchChat: () => ({ data: { icon: '' } }),
+  useGetChatSearchParams: () => mockUseGetChatSearchParams(),
+}));
+jest.mock('@/hooks/use-user-setting-request', () => ({
+  useFetchUserInfo: () => ({ data: { nickname: '', avatar: '' } }),
+}));
+jest.mock('@/utils/chat', () => ({
+  buildMessageUuidWithRole: () => 'message-key',
+}));
+jest.mock('../../hooks/use-button-disabled', () => ({
+  useGetSendButtonDisabled: () => false,
+  useSendButtonDisabled: () => false,
+}));
+jest.mock('../../hooks/use-create-conversation', () => ({
+  useCreateConversationBeforeUploadDocument: () => ({
+    createConversationBeforeUploadDocument: jest.fn(),
+  }),
+}));
+jest.mock('../../hooks/use-send-chat-message', () => ({
+  useSendMessage: () => ({
+    value: '',
+    scrollRef: { current: null },
+    messageContainerRef: { current: null },
+    sendLoading: false,
+    messages: [],
+    isUploading: false,
+    handleInputChange: jest.fn(),
+    handlePressEnter: jest.fn(),
+    regenerateMessage: jest.fn(),
+    removeMessageById: jest.fn(),
+    handleUploadFile: jest.fn(),
+    removeFile: jest.fn(),
+    hydrateFromServer: mockHydrateFromServer,
+    stopOutputMessage: jest.fn(),
+  }),
+}));
+jest.mock('../../utils', () => ({
+  buildMessageItemReference: () => undefined,
+}));
+jest.mock('../use-show-internet', () => ({
+  useShowInternet: () => false,
+}));
+
+function buildConversation(id: string) {
+  return {
+    id,
+    chat_id: 'chat-id',
+    name: 'Conversation',
+    avatar: '',
+    create_date: '',
+    create_time: 0,
+    update_date: '',
+    update_time: 0,
+    is_new: true as const,
+    reference: [],
+    messages: [
+      {
+        id: 'old-message',
+        role: MessageType.User,
+        content: 'Old conversation message',
+      },
+    ],
+  };
+}
+
+describe('SingleChatBox conversation hydration', () => {
+  beforeEach(() => {
+    mockHydrateFromServer.mockClear();
+    mockUseGetChatSearchParams.mockReset();
+  });
+
+  it('ignores stale messages while the URL points to a new conversation', () => {
+    mockUseGetChatSearchParams.mockReturnValue({
+      conversationId: 'new-conversation',
+    });
+
+    render(
+      <SingleChatBox conversation={buildConversation('old-conversation')} />,
+    );
+
+    expect(mockHydrateFromServer).not.toHaveBeenCalled();
+  });
+
+  it('hydrates messages when the conversation matches the URL', async () => {
+    const conversation = buildConversation('current-conversation');
+    mockUseGetChatSearchParams.mockReturnValue({
+      conversationId: conversation.id,
+    });
+
+    render(<SingleChatBox conversation={conversation} />);
+
+    await waitFor(() => {
+      expect(mockHydrateFromServer).toHaveBeenCalledWith(
+        conversation.id,
+        conversation.messages,
+      );
+    });
+  });
+});