fix(auth): redirect to login page on session expiry

Previously when the session expired, the API client cleared tokens but
the UI displayed "Invalid or expired token" instead of redirecting to
the login page. The root cause was that isAuthenticatedAtom was derived
from userAtom only as a re-evaluation trigger, while the actual value
came from apiClient.isAuthenticated(). On page reload userAtom is null,
so setting it to null on session expiry did not trigger a re-render and
ProtectedRoute never redirected.

Make userAtom (persisted via atomWithStorage) the single source of truth
for auth state, derive isAuthenticatedAtom from it, drop the redundant
apiClient.isAuthenticated(), and explicitly navigate to /login on
session expiry. Also trigger session expiry when a 401 comes back with
no refresh token available.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

11 files changed, 44 insertions, 79 deletions

diff --git a/src/client/App.test.tsx b/src/client/App.test.tsx
index 189a8e1..5b1607c 100644
--- a/src/client/App.test.tsx
+++ b/src/client/App.test.tsx
@@ -8,13 +8,12 @@ import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { Router } from "wouter";
 import { memoryLocation } from "wouter/memory-location";
 import { App } from "./App";
-import { authLoadingAtom } from "./atoms";
+import { authLoadingAtom, userAtom } from "./atoms";
 
 vi.mock("./api/client", () => ({
 	apiClient: {
 		login: vi.fn(),
 		logout: vi.fn(),
-		isAuthenticated: vi.fn(),
 		getTokens: vi.fn(),
 		getAuthHeader: vi.fn(),
 		onSessionExpired: vi.fn(() => vi.fn()),
@@ -52,10 +51,17 @@ function mockResponse(data: {
 	>;
 }
 
-function renderWithRouter(path: string) {
+function renderWithRouter(
+	path: string,
+	{ isAuthenticated = false }: { isAuthenticated?: boolean } = {},
+) {
 	const { hook } = memoryLocation({ path, static: true });
 	const store = createStore();
 	store.set(authLoadingAtom, false);
+	store.set(
+		userAtom,
+		isAuthenticated ? { id: "u1", username: "tester" } : null,
+	);
 	return render(
 		<Provider store={store}>
 			<Router hook={hook}>
@@ -68,7 +74,6 @@ function renderWithRouter(path: string) {
 beforeEach(() => {
 	vi.clearAllMocks();
 	vi.mocked(apiClient.getTokens).mockReturnValue(null);
-	vi.mocked(apiClient.isAuthenticated).mockReturnValue(false);
 });
 
 afterEach(() => {
@@ -83,7 +88,6 @@ describe("App routing", () => {
 				accessToken: "access-token",
 				refreshToken: "refresh-token",
 			});
-			vi.mocked(apiClient.isAuthenticated).mockReturnValue(true);
 			vi.mocked(apiClient.getAuthHeader).mockReturnValue({
 				Authorization: "Bearer access-token",
 			});
@@ -96,7 +100,7 @@ describe("App routing", () => {
 		});
 
 		it("renders home page at /", () => {
-			renderWithRouter("/");
+			renderWithRouter("/", { isAuthenticated: true });
 			expect(screen.getByRole("heading", { name: "Kioku" })).toBeDefined();
 			expect(screen.getByRole("heading", { name: "Your Decks" })).toBeDefined();
 		});
@@ -105,7 +109,6 @@ describe("App routing", () => {
 	describe("when not authenticated", () => {
 		beforeEach(() => {
 			vi.mocked(apiClient.getTokens).mockReturnValue(null);
-			vi.mocked(apiClient.isAuthenticated).mockReturnValue(false);
 		});
 
 		it("redirects to login when accessing / without authentication", () => {
diff --git a/src/client/api/client.test.ts b/src/client/api/client.test.ts
index 27c3a0a..e2d314f 100644
--- a/src/client/api/client.test.ts
+++ b/src/client/api/client.test.ts
@@ -119,27 +119,6 @@ describe("ApiClient", () => {
 		});
 	});
 
-	describe("isAuthenticated", () => {
-		it("returns true when tokens exist", () => {
-			const mockStorage = createMockTokenStorage();
-			mockStorage.getTokens.mockReturnValue({
-				accessToken: "token",
-				refreshToken: "refresh",
-			});
-			const client = new ApiClient({ tokenStorage: mockStorage });
-
-			expect(client.isAuthenticated()).toBe(true);
-		});
-
-		it("returns false when no tokens", () => {
-			const mockStorage = createMockTokenStorage();
-			mockStorage.getTokens.mockReturnValue(null);
-			const client = new ApiClient({ tokenStorage: mockStorage });
-
-			expect(client.isAuthenticated()).toBe(false);
-		});
-	});
-
 	describe("getAuthHeader", () => {
 		it("returns auth header when tokens exist", () => {
 			const mockStorage = createMockTokenStorage();
diff --git a/src/client/api/client.ts b/src/client/api/client.ts
index fc718a2..539df8b 100644
--- a/src/client/api/client.ts
+++ b/src/client/api/client.ts
@@ -101,16 +101,22 @@ export class ApiClient {
 
 		const response = await fetch(input, { ...init, headers });
 
-		if (response.status === 401 && tokens?.refreshToken) {
-			// Try to refresh the token
-			const refreshed = await this.refreshToken();
-			if (refreshed) {
-				// Retry with new token
-				const newTokens = this.tokenStorage.getTokens();
-				if (newTokens?.accessToken) {
-					headers.set("Authorization", `Bearer ${newTokens.accessToken}`);
+		if (response.status === 401 && tokens?.accessToken) {
+			if (tokens.refreshToken) {
+				// Try to refresh the token
+				const refreshed = await this.refreshToken();
+				if (refreshed) {
+					// Retry with new token
+					const newTokens = this.tokenStorage.getTokens();
+					if (newTokens?.accessToken) {
+						headers.set("Authorization", `Bearer ${newTokens.accessToken}`);
+					}
+					return fetch(input, { ...init, headers });
 				}
-				return fetch(input, { ...init, headers });
+			} else {
+				// No refresh token available — treat as session expiry
+				this.tokenStorage.clearTokens();
+				this.sessionExpiredCallback?.();
 			}
 		}
 
@@ -205,10 +211,6 @@ export class ApiClient {
 		this.tokenStorage.clearTokens();
 	}
 
-	isAuthenticated(): boolean {
-		return this.tokenStorage.getTokens() !== null;
-	}
-
 	getTokens(): Tokens | null {
 		return this.tokenStorage.getTokens();
 	}
diff --git a/src/client/atoms/auth.ts b/src/client/atoms/auth.ts
index f618ccf..9ee69cf 100644
--- a/src/client/atoms/auth.ts
+++ b/src/client/atoms/auth.ts
@@ -1,17 +1,18 @@
 import { atom, useSetAtom } from "jotai";
+import { atomWithStorage } from "jotai/utils";
 import { useEffect } from "react";
+import { useLocation } from "wouter";
 import { apiClient, type User } from "../api/client";
 
-// Primitive atoms
-export const userAtom = atom<User | null>(null);
+// userAtom is the single source of truth for auth state. Persisted to
+// localStorage so that the authenticated user survives page reloads alongside
+// the tokens in apiClient's token storage.
+export const userAtom = atomWithStorage<User | null>("kioku_user", null);
 export const authLoadingAtom = atom<boolean>(true);
 
-// Derived atom - checks if user is authenticated via apiClient
-export const isAuthenticatedAtom = atom<boolean>((get) => {
-	// We need to trigger re-evaluation when user changes
-	get(userAtom);
-	return apiClient.isAuthenticated();
-});
+export const isAuthenticatedAtom = atom<boolean>(
+	(get) => get(userAtom) !== null,
+);
 
 // Action atom - login
 export const loginAtom = atom(
@@ -36,22 +37,18 @@ export const logoutAtom = atom(null, (_get, set) => {
 export function useAuthInit() {
 	const setAuthLoading = useSetAtom(authLoadingAtom);
 	const setUser = useSetAtom(userAtom);
+	const [, navigate] = useLocation();
 
 	useEffect(() => {
-		// Check for existing auth on mount
-		const tokens = apiClient.getTokens();
-		if (tokens) {
-			// We have tokens stored, but we don't have user info cached
-			// For now, just set authenticated state. User info will be fetched when needed.
-		}
 		setAuthLoading(false);
 
 		// Subscribe to session expired events from the API client
 		const unsubscribe = apiClient.onSessionExpired(() => {
 			apiClient.logout();
 			setUser(null);
+			navigate("/login", { replace: true });
 		});
 
 		return unsubscribe;
-	}, [setAuthLoading, setUser]);
+	}, [setAuthLoading, setUser, navigate]);
 }
diff --git a/src/client/components/ProtectedRoute.test.tsx b/src/client/components/ProtectedRoute.test.tsx
index 64a0678..0cf97e3 100644
--- a/src/client/components/ProtectedRoute.test.tsx
+++ b/src/client/components/ProtectedRoute.test.tsx
@@ -6,14 +6,13 @@ import { createStore, Provider } from "jotai";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { Router } from "wouter";
 import { memoryLocation } from "wouter/memory-location";
-import { authLoadingAtom } from "../atoms";
+import { authLoadingAtom, userAtom } from "../atoms";
 import { ProtectedRoute } from "./ProtectedRoute";
 
 vi.mock("../api/client", () => ({
 	apiClient: {
 		login: vi.fn(),
 		logout: vi.fn(),
-		isAuthenticated: vi.fn(),
 		getTokens: vi.fn(),
 		onSessionExpired: vi.fn(() => vi.fn()),
 	},
@@ -29,20 +28,17 @@ vi.mock("../api/client", () => ({
 	},
 }));
 
-import { apiClient } from "../api/client";
-
 function renderWithProvider(
 	path: string,
 	atomValues: { isAuthenticated: boolean; isLoading: boolean },
 ) {
-	// Mock the apiClient.isAuthenticated to control isAuthenticatedAtom value
-	vi.mocked(apiClient.isAuthenticated).mockReturnValue(
-		atomValues.isAuthenticated,
-	);
-
 	const { hook } = memoryLocation({ path });
 	const store = createStore();
 	store.set(authLoadingAtom, atomValues.isLoading);
+	store.set(
+		userAtom,
+		atomValues.isAuthenticated ? { id: "u1", username: "tester" } : null,
+	);
 
 	return render(
 		<Provider store={store}>
diff --git a/src/client/pages/DeckCardsPage.test.tsx b/src/client/pages/DeckCardsPage.test.tsx
index 6e8f444..c498056 100644
--- a/src/client/pages/DeckCardsPage.test.tsx
+++ b/src/client/pages/DeckCardsPage.test.tsx
@@ -22,7 +22,6 @@ vi.mock("../api/client", () => ({
 	apiClient: {
 		login: vi.fn(),
 		logout: vi.fn(),
-		isAuthenticated: vi.fn(),
 		getTokens: vi.fn(),
 		getAuthHeader: vi.fn(),
 		onSessionExpired: vi.fn(() => vi.fn()),
@@ -228,7 +227,6 @@ describe("DeckCardsPage", () => {
 			accessToken: "access-token",
 			refreshToken: "refresh-token",
 		});
-		vi.mocked(apiClient.isAuthenticated).mockReturnValue(true);
 		vi.mocked(apiClient.getAuthHeader).mockReturnValue({
 			Authorization: "Bearer access-token",
 		});
diff --git a/src/client/pages/DeckDetailPage.test.tsx b/src/client/pages/DeckDetailPage.test.tsx
index c473275..a63d8a9 100644
--- a/src/client/pages/DeckDetailPage.test.tsx
+++ b/src/client/pages/DeckDetailPage.test.tsx
@@ -20,7 +20,6 @@ vi.mock("../api/client", () => ({
 	apiClient: {
 		login: vi.fn(),
 		logout: vi.fn(),
-		isAuthenticated: vi.fn(),
 		getTokens: vi.fn(),
 		getAuthHeader: vi.fn(),
 		onSessionExpired: vi.fn(() => vi.fn()),
@@ -165,7 +164,6 @@ describe("DeckDetailPage", () => {
 			accessToken: "access-token",
 			refreshToken: "refresh-token",
 		});
-		vi.mocked(apiClient.isAuthenticated).mockReturnValue(true);
 		vi.mocked(apiClient.getAuthHeader).mockReturnValue({
 			Authorization: "Bearer access-token",
 		});
diff --git a/src/client/pages/HomePage.test.tsx b/src/client/pages/HomePage.test.tsx
index adcc651..a552c7f 100644
--- a/src/client/pages/HomePage.test.tsx
+++ b/src/client/pages/HomePage.test.tsx
@@ -22,7 +22,6 @@ vi.mock("../api/client", () => ({
 	apiClient: {
 		login: vi.fn(),
 		logout: vi.fn(),
-		isAuthenticated: vi.fn(),
 		getTokens: vi.fn(),
 		getAuthHeader: vi.fn(),
 		onSessionExpired: vi.fn(() => vi.fn()),
@@ -152,7 +151,6 @@ describe("HomePage", () => {
 			accessToken: "access-token",
 			refreshToken: "refresh-token",
 		});
-		vi.mocked(apiClient.isAuthenticated).mockReturnValue(true);
 		vi.mocked(apiClient.getAuthHeader).mockReturnValue({
 			Authorization: "Bearer access-token",
 		});
diff --git a/src/client/pages/LoginPage.test.tsx b/src/client/pages/LoginPage.test.tsx
index 6ed4011..b559bff 100644
--- a/src/client/pages/LoginPage.test.tsx
+++ b/src/client/pages/LoginPage.test.tsx
@@ -7,14 +7,13 @@ import { createStore, Provider } from "jotai";
 import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
 import { Router } from "wouter";
 import { memoryLocation } from "wouter/memory-location";
-import { authLoadingAtom } from "../atoms";
+import { authLoadingAtom, userAtom } from "../atoms";
 import { LoginPage } from "./LoginPage";
 
 vi.mock("../api/client", () => ({
 	apiClient: {
 		login: vi.fn(),
 		logout: vi.fn(),
-		isAuthenticated: vi.fn(),
 		getTokens: vi.fn(),
 		onSessionExpired: vi.fn(() => vi.fn()),
 	},
@@ -49,7 +48,6 @@ describe("LoginPage", () => {
 	beforeEach(() => {
 		vi.clearAllMocks();
 		vi.mocked(apiClient.getTokens).mockReturnValue(null);
-		vi.mocked(apiClient.isAuthenticated).mockReturnValue(false);
 	});
 
 	afterEach(() => {
@@ -147,7 +145,6 @@ describe("LoginPage", () => {
 	});
 
 	it("redirects when already authenticated", async () => {
-		vi.mocked(apiClient.isAuthenticated).mockReturnValue(true);
 		vi.mocked(apiClient.getTokens).mockReturnValue({
 			accessToken: "access-token",
 			refreshToken: "refresh-token",
@@ -162,6 +159,7 @@ describe("LoginPage", () => {
 
 		const store = createStore();
 		store.set(authLoadingAtom, false);
+		store.set(userAtom, { id: "u1", username: "tester" });
 
 		render(
 			<Provider store={store}>
diff --git a/src/client/pages/NoteTypesPage.test.tsx b/src/client/pages/NoteTypesPage.test.tsx
index ac68e35..612cf16 100644
--- a/src/client/pages/NoteTypesPage.test.tsx
+++ b/src/client/pages/NoteTypesPage.test.tsx
@@ -29,7 +29,6 @@ vi.mock("../api/client", () => ({
 	apiClient: {
 		login: vi.fn(),
 		logout: vi.fn(),
-		isAuthenticated: vi.fn(),
 		getTokens: vi.fn(),
 		getAuthHeader: vi.fn(),
 		onSessionExpired: vi.fn(() => vi.fn()),
@@ -126,7 +125,6 @@ describe("NoteTypesPage", () => {
 			accessToken: "access-token",
 			refreshToken: "refresh-token",
 		});
-		vi.mocked(apiClient.isAuthenticated).mockReturnValue(true);
 		vi.mocked(apiClient.getAuthHeader).mockReturnValue({
 			Authorization: "Bearer access-token",
 		});
diff --git a/src/client/pages/StudyPage.test.tsx b/src/client/pages/StudyPage.test.tsx
index 860777a..d9e9d64 100644
--- a/src/client/pages/StudyPage.test.tsx
+++ b/src/client/pages/StudyPage.test.tsx
@@ -74,7 +74,6 @@ vi.mock("../api/client", () => ({
 	apiClient: {
 		login: vi.fn(),
 		logout: vi.fn(),
-		isAuthenticated: vi.fn(),
 		getTokens: vi.fn(),
 		getAuthHeader: vi.fn(),
 		onSessionExpired: vi.fn(() => vi.fn()),
@@ -212,7 +211,6 @@ describe("StudyPage", () => {
 			accessToken: "access-token",
 			refreshToken: "refresh-token",
 		});
-		vi.mocked(apiClient.isAuthenticated).mockReturnValue(true);
 		vi.mocked(apiClient.getAuthHeader).mockReturnValue({
 			Authorization: "Bearer access-token",
 		});