fix: opening /ai-assistant opens 2 new conversations instead of one

frontend/src/pages/AIAssistantPage/AIAssistantPage.tsx

@@ -26,8 +26,8 @@ export default function AIAssistantPage(): JSX.Element {
 
 	// Skip the mount-time Opened fire when the user expanded an already-open
 	// drawer/modal — that surface already emitted Opened with the right source.
-	// Router state (vs a module flag) survives StrictMode double-mount and
-	// aborted navigations.
+	// Router state (vs a module flag) survives page remounts and aborted
+	// navigations.
 	const fromInApp = location.state?.fromInApp === true;
 	useEffect(() => {
 		if (fromInApp) {
@@ -52,18 +52,34 @@ export default function AIAssistantPage(): JSX.Element {
 		(s) => s.startNewConversation,
 	);
 
-	// Keep a ref so the effect can read latest conversations without re-firing
-	// when startNewConversation mutates the store mid-effect.
+	// Keep refs so the effect can read the latest store state without re-firing
+	// when it mutates the store mid-effect (it only depends on the URL param).
 	const conversationsRef = useRef(conversations);
 	conversationsRef.current = conversations;
+	const activeConversationIdRef = useRef(activeConversationId);
+	activeConversationIdRef.current = activeConversationId;
 
 	useEffect(() => {
-		if (conversationsRef.current[conversationId]) {
+		// URL points at a known conversation → just activate it.
+		if (conversationId && conversationsRef.current[conversationId]) {
 			setActiveConversation(conversationId);
-		} else {
-			const newId = startNewConversation();
-			history.replace(ROUTES.AI_ASSISTANT.replace(':conversationId', newId));
+			return;
 		}
+
+		// The URL has no usable conversation id (bare `/ai-assistant`, or a stale
+		// param). Prefer resuming the active conversation — including the
+		// rehydrating placeholder for the persisted thread — over minting a new
+		// one. This is what stops a throwaway blank chat from flashing as a
+		// second thread during load, and stops a duplicate when the page
+		// remounts during startup route churn (the active id is already set, so
+		// we resume instead of create). Starting fresh is the last resort, only
+		// when there is genuinely nothing to resume.
+		const activeId = activeConversationIdRef.current;
+		const resumeId =
+			activeId && conversationsRef.current[activeId]
+				? activeId
+				: startNewConversation();
+		history.replace(ROUTES.AI_ASSISTANT.replace(':conversationId', resumeId));
 		// Only re-run when the URL param changes, not when conversations mutates.
 		// eslint-disable-next-line react-hooks/exhaustive-deps
 	}, [conversationId]);

frontend/src/pages/AIAssistantPage/__tests__/AIAssistantPage.test.tsx

@@ -0,0 +1,181 @@
+import { MemoryRouter, Route } from 'react-router-dom';
+// eslint-disable-next-line no-restricted-imports
+import { render } from '@testing-library/react';
+import ROUTES from 'constants/routes';
+import { useAIAssistantStore } from 'container/AIAssistant/store/useAIAssistantStore';
+
+jest.mock('api/common/logEvent', () => ({
+	__esModule: true,
+	default: jest.fn(),
+}));
+
+jest.mock('container/AIAssistant/ConversationView', () => ({
+	__esModule: true,
+	default: (): JSX.Element => <div data-testid="conversation-view" />,
+}));
+
+jest.mock('container/AIAssistant/components/ConversationsList', () => ({
+	__esModule: true,
+	default: (): JSX.Element => <div data-testid="conversations-list" />,
+}));
+
+jest.mock('components/Noz/Noz', () => ({
+	__esModule: true,
+	default: (): JSX.Element => <div data-testid="noz" />,
+}));
+
+jest.mock('container/AIAssistant/hooks/useAIAssistantAnalyticsContext', () => ({
+	normalizePage: (page: string): string => page,
+	useAIAssistantAnalyticsContext: (): unknown => ({ mode: 'page' }),
+}));
+
+// eslint-disable-next-line import/first
+import AIAssistantPage from '../AIAssistantPage';
+
+function renderAt(entry: string): { unmount: () => void } {
+	return render(
+		<MemoryRouter initialEntries={[entry]}>
+			<Route
+				exact
+				path={[ROUTES.AI_ASSISTANT_BASE, ROUTES.AI_ASSISTANT]}
+				component={AIAssistantPage}
+			/>
+		</MemoryRouter>,
+	);
+}
+
+function renderAtBase(): { unmount: () => void } {
+	return renderAt(ROUTES.AI_ASSISTANT_BASE);
+}
+
+function conversationCount(): number {
+	return Object.keys(useAIAssistantStore.getState().conversations).length;
+}
+
+function conversationIds(): string[] {
+	return Object.keys(useAIAssistantStore.getState().conversations);
+}
+
+function activeId(): string | null {
+	return useAIAssistantStore.getState().activeConversationId;
+}
+
+describe('AIAssistantPage', () => {
+	beforeEach(() => {
+		useAIAssistantStore.setState({
+			conversations: {},
+			streams: {},
+			activeConversationId: null,
+		});
+	});
+
+	it('opens exactly one conversation when navigating to /ai-assistant', () => {
+		const { unmount } = renderAtBase();
+
+		expect(conversationCount()).toBe(1);
+
+		unmount();
+	});
+
+	it('does not stack a second conversation when the page remounts at the bare URL (route churn)', () => {
+		// First mount at `/ai-assistant` creates one blank conversation and
+		// redirects to `/ai-assistant/:id`.
+		const { unmount } = renderAtBase();
+		expect(conversationCount()).toBe(1);
+		const firstId = conversationIds()[0];
+
+		// Startup route-list churn unmounts and remounts the page while the URL
+		// is momentarily back at the bare `/ai-assistant`. This previously
+		// created a second blank conversation — now it reuses the first.
+		unmount();
+		const { unmount: unmount2 } = renderAtBase();
+
+		expect(conversationCount()).toBe(1);
+		// The surviving conversation is the original one, resumed — not a fresh mint.
+		expect(conversationIds()).toStrictEqual([firstId]);
+		expect(activeId()).toBe(firstId);
+
+		unmount2();
+	});
+
+	it('activates the conversation named in the URL without creating a new one', () => {
+		useAIAssistantStore.setState({
+			conversations: {
+				existing: {
+					id: 'existing',
+					messages: [],
+					createdAt: 1,
+					updatedAt: 1,
+				},
+			},
+			streams: {},
+			activeConversationId: null,
+		});
+
+		const { unmount } = renderAt(
+			ROUTES.AI_ASSISTANT.replace(':conversationId', 'existing'),
+		);
+
+		expect(conversationCount()).toBe(1);
+		expect(activeId()).toBe('existing');
+
+		unmount();
+	});
+
+	it('resumes the active conversation on /ai-assistant/new instead of minting a new one', () => {
+		// The sidenav only routes to `/ai-assistant/new` as a fallback, but if an
+		// active conversation exists the page must resume it rather than spawn a
+		// throwaway blank thread for the unknown "new" param.
+		useAIAssistantStore.setState({
+			conversations: {
+				active: {
+					id: 'active',
+					messages: [],
+					createdAt: 1,
+					updatedAt: 1,
+				},
+			},
+			streams: {},
+			activeConversationId: 'active',
+		});
+
+		const { unmount } = renderAt(
+			ROUTES.AI_ASSISTANT.replace(':conversationId', 'new'),
+		);
+
+		expect(conversationCount()).toBe(1);
+		expect(conversationIds()).toStrictEqual(['active']);
+		expect(activeId()).toBe('active');
+
+		unmount();
+	});
+
+	it('resumes the persisted (hydrating) conversation during load instead of creating a second', () => {
+		// Simulates `onRehydrateStorage` priming the persisted active
+		// conversation as a hydrating placeholder before `fetchThreads` resolves.
+		useAIAssistantStore.setState({
+			conversations: {
+				persisted: {
+					id: 'persisted',
+					messages: [],
+					createdAt: 1,
+					updatedAt: 1,
+					isHydrating: true,
+				},
+			},
+			streams: {},
+			activeConversationId: 'persisted',
+		});
+
+		const { unmount } = renderAtBase();
+
+		// Opening the bare URL must resume the persisted conversation, not mint a
+		// throwaway blank alongside it (which flashed as a 2nd thread during load).
+		expect(conversationCount()).toBe(1);
+		expect(
+			Object.keys(useAIAssistantStore.getState().conversations),
+		).toStrictEqual(['persisted']);
+
+		unmount();
+	});
+});