diff --git a/mobile/src/lib/auth-helpers.test.ts b/mobile/src/lib/auth-helpers.test.ts
new file mode 100644
index 0000000..1d92b98
--- /dev/null
+++ b/mobile/src/lib/auth-helpers.test.ts
@@ -0,0 +1,23 @@
+import { beforeEach, describe, expect, it } from 'vitest';
+import { PRODUCT_ID } from '../api/config';
+import { mmkvStorage } from '../store/mmkv-storage';
+import { AUTH_ACCESS_TOKEN_KEY, getAccessToken } from './auth-helpers';
+
+describe('mobile auth helpers', () => {
+  beforeEach(() => {
+    mmkvStorage.removeItem(`${PRODUCT_ID}_access_token`);
+    mmkvStorage.removeItem(`${PRODUCT_ID}-auth-token`);
+  });
+
+  it('reads the shared auth-client access token key', () => {
+    mmkvStorage.setItem(AUTH_ACCESS_TOKEN_KEY, 'platform-token');
+
+    expect(getAccessToken()).toBe('platform-token');
+  });
+
+  it('does not read the legacy mobile-only token key', () => {
+    mmkvStorage.setItem(`${PRODUCT_ID}_access_token`, 'legacy-token');
+
+    expect(getAccessToken()).toBeNull();
+  });
+});
diff --git a/mobile/src/lib/auth-helpers.ts b/mobile/src/lib/auth-helpers.ts
index 182bad9..d99875b 100644
--- a/mobile/src/lib/auth-helpers.ts
+++ b/mobile/src/lib/auth-helpers.ts
@@ -1,6 +1,8 @@
 import { PRODUCT_ID } from '../api/config';
 import { mmkvStorage } from '../store/mmkv-storage';
 
+export const AUTH_ACCESS_TOKEN_KEY = `${PRODUCT_ID}-auth-token`;
+
 export function getAccessToken(): string | null {
-  return mmkvStorage.getItem(`${PRODUCT_ID}_access_token`);
+  return mmkvStorage.getItem(AUTH_ACCESS_TOKEN_KEY);
 }
diff --git a/mobile/src/store/auth-store.test.ts b/mobile/src/store/auth-store.test.ts
index 7da8368..69d52e6 100644
--- a/mobile/src/store/auth-store.test.ts
+++ b/mobile/src/store/auth-store.test.ts
@@ -1,10 +1,13 @@
 import { describe, expect, it, vi, beforeEach } from 'vitest';
+import { PRODUCT_ID } from '../api/config';
+import { mmkvStorage } from './mmkv-storage';
 
 const isAuthenticatedMock = vi.fn();
 const getMeMock = vi.fn();
 const loginMock = vi.fn();
 const registerMock = vi.fn();
 const clearTokensMock = vi.fn();
+const refreshAccessTokenMock = vi.fn();
 
 vi.mock('../api/auth', () => ({
   getAuthClient: () => ({
@@ -12,6 +15,7 @@ vi.mock('../api/auth', () => ({
     getMe: getMeMock,
     login: loginMock,
     register: registerMock,
+    refreshAccessToken: refreshAccessTokenMock,
     clearTokens: clearTokensMock,
     getAccessToken: vi.fn(() => null),
   }),
@@ -20,6 +24,7 @@ vi.mock('../api/auth', () => ({
 import { useAuthStore } from './auth-store';
 
 function resetStore() {
+  mmkvStorage.removeItem(`${PRODUCT_ID}-auth-email`);
   useAuthStore.setState({
     hasBootstrapped: false,
     isAuthenticated: false,
@@ -41,67 +46,143 @@ describe('useAuthStore', () => {
     expect(useAuthStore.getState().hasBootstrapped).toBe(true);
     expect(useAuthStore.getState().isAuthenticated).toBe(true);
     expect(useAuthStore.getState().email).toBe('test@example.com');
+    expect(mmkvStorage.getItem(`${PRODUCT_ID}-auth-email`)).toBe('test@example.com');
   });
 
   it('bootstrap sets unauthenticated when no token', async () => {
     isAuthenticatedMock.mockReturnValue(false);
+    mmkvStorage.setItem(`${PRODUCT_ID}-auth-email`, 'cached@example.com');
     await useAuthStore.getState().bootstrap();
     expect(useAuthStore.getState().hasBootstrapped).toBe(true);
     expect(useAuthStore.getState().isAuthenticated).toBe(false);
     expect(useAuthStore.getState().email).toBeNull();
+    expect(mmkvStorage.getItem(`${PRODUCT_ID}-auth-email`)).toBeNull();
   });
 
-  it('bootstrap clears tokens on getMe failure', async () => {
+  it('bootstrap preserves a valid local session during offline startup', async () => {
     isAuthenticatedMock.mockReturnValue(true);
-    getMeMock.mockRejectedValueOnce(new Error('expired'));
+    mmkvStorage.setItem(`${PRODUCT_ID}-auth-email`, 'cached@example.com');
+    getMeMock.mockRejectedValueOnce(new Error('Network request failed'));
+    await useAuthStore.getState().bootstrap();
+    expect(clearTokensMock).not.toHaveBeenCalled();
+    expect(useAuthStore.getState().hasBootstrapped).toBe(true);
+    expect(useAuthStore.getState().isAuthenticated).toBe(true);
+    expect(useAuthStore.getState().email).toBe('cached@example.com');
+  });
+
+  it('bootstrap refreshes an expired token before clearing the session', async () => {
+    isAuthenticatedMock.mockReturnValue(true);
+    getMeMock.mockRejectedValueOnce(new Error('HTTP 401'));
+    refreshAccessTokenMock.mockResolvedValueOnce(true);
+    getMeMock.mockResolvedValueOnce({ email: 'fresh@example.com' });
+    await useAuthStore.getState().bootstrap();
+    expect(refreshAccessTokenMock).toHaveBeenCalled();
+    expect(clearTokensMock).not.toHaveBeenCalled();
+    expect(useAuthStore.getState().hasBootstrapped).toBe(true);
+    expect(useAuthStore.getState().isAuthenticated).toBe(true);
+    expect(useAuthStore.getState().email).toBe('fresh@example.com');
+  });
+
+  it('bootstrap clears tokens on non-refreshable getMe failure', async () => {
+    isAuthenticatedMock.mockReturnValue(true);
+    mmkvStorage.setItem(`${PRODUCT_ID}-auth-email`, 'cached@example.com');
+    getMeMock.mockRejectedValueOnce(new Error('invalid account'));
     await useAuthStore.getState().bootstrap();
     expect(clearTokensMock).toHaveBeenCalled();
     expect(useAuthStore.getState().hasBootstrapped).toBe(true);
     expect(useAuthStore.getState().isAuthenticated).toBe(false);
+    expect(mmkvStorage.getItem(`${PRODUCT_ID}-auth-email`)).toBeNull();
   });
 
   it('signIn sets authenticated on success', async () => {
-    loginMock.mockResolvedValueOnce(undefined);
+    loginMock.mockResolvedValueOnce({
+      accessToken: 'access',
+      refreshToken: 'refresh',
+      user: { email: 'test@example.com' },
+    });
     const ok = await useAuthStore.getState().signIn('test@example.com', 'pass');
     expect(ok).toBe(true);
+    expect(loginMock).toHaveBeenCalledWith('test@example.com', 'pass');
     expect(useAuthStore.getState().hasBootstrapped).toBe(true);
     expect(useAuthStore.getState().isAuthenticated).toBe(true);
     expect(useAuthStore.getState().email).toBe('test@example.com');
+    expect(mmkvStorage.getItem(`${PRODUCT_ID}-auth-email`)).toBe('test@example.com');
+  });
+
+  it('signIn returns false when the platform requires MFA', async () => {
+    loginMock.mockResolvedValueOnce({ mfaRequired: true, mfaChallenge: 'challenge', methods: ['totp'] });
+    const ok = await useAuthStore.getState().signIn('test@example.com', 'pass');
+    expect(ok).toBe(false);
+    expect(useAuthStore.getState().isAuthenticated).toBe(false);
+    expect(clearTokensMock).toHaveBeenCalled();
   });
 
   it('signIn returns false on failure', async () => {
     loginMock.mockRejectedValueOnce(new Error('bad credentials'));
+    mmkvStorage.setItem(`${PRODUCT_ID}-auth-email`, 'old@example.com');
     const ok = await useAuthStore.getState().signIn('bad@example.com', 'wrong');
     expect(ok).toBe(false);
     expect(useAuthStore.getState().hasBootstrapped).toBe(true);
     expect(useAuthStore.getState().isAuthenticated).toBe(false);
     expect(clearTokensMock).toHaveBeenCalled();
+    expect(mmkvStorage.getItem(`${PRODUCT_ID}-auth-email`)).toBeNull();
   });
 
   it('register sets authenticated on success', async () => {
-    registerMock.mockResolvedValueOnce(undefined);
+    registerMock.mockResolvedValueOnce({
+      accessToken: 'access',
+      refreshToken: 'refresh',
+      user: { email: 'new@example.com' },
+    });
     const ok = await useAuthStore.getState().register('new@example.com', 'pass', 'New User');
     expect(ok).toBe(true);
+    expect(registerMock).toHaveBeenCalledWith('new@example.com', 'pass', 'New User');
     expect(useAuthStore.getState().hasBootstrapped).toBe(true);
     expect(useAuthStore.getState().isAuthenticated).toBe(true);
     expect(useAuthStore.getState().email).toBe('new@example.com');
+    expect(mmkvStorage.getItem(`${PRODUCT_ID}-auth-email`)).toBe('new@example.com');
   });
 
   it('register returns false on failure', async () => {
     registerMock.mockRejectedValueOnce(new Error('register failed'));
+    mmkvStorage.setItem(`${PRODUCT_ID}-auth-email`, 'old@example.com');
     const ok = await useAuthStore.getState().register('bad@example.com', 'wrong', 'Bad');
     expect(ok).toBe(false);
     expect(useAuthStore.getState().hasBootstrapped).toBe(true);
     expect(useAuthStore.getState().isAuthenticated).toBe(false);
     expect(clearTokensMock).toHaveBeenCalled();
+    expect(mmkvStorage.getItem(`${PRODUCT_ID}-auth-email`)).toBeNull();
+  });
+
+  it('refreshSession keeps authenticated state on refresh success', async () => {
+    isAuthenticatedMock.mockReturnValue(true);
+    refreshAccessTokenMock.mockResolvedValueOnce(true);
+    getMeMock.mockResolvedValueOnce({ email: 'fresh@example.com' });
+    const ok = await useAuthStore.getState().refreshSession();
+    expect(ok).toBe(true);
+    expect(refreshAccessTokenMock).toHaveBeenCalled();
+    expect(useAuthStore.getState().isAuthenticated).toBe(true);
+    expect(useAuthStore.getState().email).toBe('fresh@example.com');
+  });
+
+  it('refreshSession clears state when refresh fails', async () => {
+    isAuthenticatedMock.mockReturnValue(true);
+    refreshAccessTokenMock.mockResolvedValueOnce(false);
+    mmkvStorage.setItem(`${PRODUCT_ID}-auth-email`, 'old@example.com');
+    const ok = await useAuthStore.getState().refreshSession();
+    expect(ok).toBe(false);
+    expect(useAuthStore.getState().isAuthenticated).toBe(false);
+    expect(mmkvStorage.getItem(`${PRODUCT_ID}-auth-email`)).toBeNull();
   });
 
   it('signOut clears state', () => {
+    mmkvStorage.setItem(`${PRODUCT_ID}-auth-email`, 'test@example.com');
     useAuthStore.setState({ hasBootstrapped: true, isAuthenticated: true, email: 'test@example.com' });
     useAuthStore.getState().signOut();
     expect(useAuthStore.getState().hasBootstrapped).toBe(true);
     expect(useAuthStore.getState().isAuthenticated).toBe(false);
     expect(useAuthStore.getState().email).toBeNull();
     expect(clearTokensMock).toHaveBeenCalled();
+    expect(mmkvStorage.getItem(`${PRODUCT_ID}-auth-email`)).toBeNull();
   });
 });
diff --git a/mobile/src/store/auth-store.ts b/mobile/src/store/auth-store.ts
index 6b37b4a..eb3bad1 100644
--- a/mobile/src/store/auth-store.ts
+++ b/mobile/src/store/auth-store.ts
@@ -1,5 +1,52 @@
 import { create } from 'zustand';
 import { getAuthClient } from '../api/auth';
+import { PRODUCT_ID } from '../api/config';
+import { mmkvStorage } from './mmkv-storage';
+
+const AUTH_EMAIL_CACHE_KEY = `${PRODUCT_ID}-auth-email`;
+
+function getCachedEmail(): string | null {
+  return mmkvStorage.getItem(AUTH_EMAIL_CACHE_KEY);
+}
+
+function setCachedEmail(email: string): void {
+  mmkvStorage.setItem(AUTH_EMAIL_CACHE_KEY, email);
+}
+
+function clearCachedEmail(): void {
+  mmkvStorage.removeItem(AUTH_EMAIL_CACHE_KEY);
+}
+
+function isOfflineStartupError(error: unknown): boolean {
+  if (!(error instanceof Error)) {
+    return false;
+  }
+
+  const message = error.message.toLowerCase();
+  return (
+    message.includes('network') ||
+    message.includes('failed to fetch') ||
+    message.includes('fetch failed') ||
+    message.includes('offline') ||
+    message.includes('timeout') ||
+    message.includes('abort')
+  );
+}
+
+function isRefreshableAuthError(error: unknown): boolean {
+  if (!(error instanceof Error)) {
+    return false;
+  }
+
+  const message = error.message.toLowerCase();
+  return (
+    message.includes('http 401') ||
+    message.includes('http 403') ||
+    message.includes('unauthorized') ||
+    message.includes('forbidden') ||
+    message.includes('expired')
+  );
+}
 
 export type AuthState = {
   hasBootstrapped: boolean;
@@ -7,6 +54,7 @@ export type AuthState = {
   isLoading: boolean;
   email: string | null;
   bootstrap: () => Promise<void>;
+  refreshSession: () => Promise<boolean>;
   signIn: (email: string, password: string) => Promise<boolean>;
   register: (email: string, password: string, displayName: string) => Promise<boolean>;
   signOut: () => void;
@@ -20,6 +68,7 @@ export const useAuthStore = create<AuthState>((set) => ({
   async bootstrap() {
     const client = getAuthClient();
     if (!client.isAuthenticated()) {
+      clearCachedEmail();
       set({ hasBootstrapped: true, isAuthenticated: false, email: null, isLoading: false });
       return;
     }
@@ -28,21 +77,86 @@ export const useAuthStore = create<AuthState>((set) => ({
 
     try {
       const me = await client.getMe();
+      setCachedEmail(me.email);
       set({ hasBootstrapped: true, isAuthenticated: true, email: me.email, isLoading: false });
-    } catch {
+    } catch (error) {
+      if (isOfflineStartupError(error) && client.isAuthenticated()) {
+        set({
+          hasBootstrapped: true,
+          isAuthenticated: true,
+          email: getCachedEmail(),
+          isLoading: false,
+        });
+        return;
+      }
+
+      if (isRefreshableAuthError(error) && (await client.refreshAccessToken())) {
+        try {
+          const me = await client.getMe();
+          setCachedEmail(me.email);
+          set({ hasBootstrapped: true, isAuthenticated: true, email: me.email, isLoading: false });
+          return;
+        } catch (refreshError) {
+          if (isOfflineStartupError(refreshError) && client.isAuthenticated()) {
+            set({
+              hasBootstrapped: true,
+              isAuthenticated: true,
+              email: getCachedEmail(),
+              isLoading: false,
+            });
+            return;
+          }
+        }
+      }
+
       client.clearTokens();
+      clearCachedEmail();
       set({ hasBootstrapped: true, isAuthenticated: false, email: null, isLoading: false });
     }
   },
+  async refreshSession() {
+    const client = getAuthClient();
+    if (!client.isAuthenticated()) {
+      clearCachedEmail();
+      set({ hasBootstrapped: true, isAuthenticated: false, email: null, isLoading: false });
+      return false;
+    }
+
+    set({ isLoading: true });
+    const refreshed = await client.refreshAccessToken();
+    if (!refreshed) {
+      clearCachedEmail();
+      set({ hasBootstrapped: true, isAuthenticated: false, email: null, isLoading: false });
+      return false;
+    }
+
+    try {
+      const me = await client.getMe();
+      setCachedEmail(me.email);
+      set({ hasBootstrapped: true, isAuthenticated: true, email: me.email, isLoading: false });
+    } catch {
+      set({ hasBootstrapped: true, isAuthenticated: true, email: getCachedEmail(), isLoading: false });
+    }
+
+    return true;
+  },
   async signIn(email: string, password: string) {
     set({ isLoading: true });
 
     try {
-      await getAuthClient().login(email, password);
-      set({ hasBootstrapped: true, isAuthenticated: true, email, isLoading: false });
+      const result = await getAuthClient().login(email, password);
+      if ('mfaRequired' in result) {
+        getAuthClient().clearTokens();
+        clearCachedEmail();
+        set({ hasBootstrapped: true, isAuthenticated: false, email: null, isLoading: false });
+        return false;
+      }
+      setCachedEmail(result.user.email);
+      set({ hasBootstrapped: true, isAuthenticated: true, email: result.user.email, isLoading: false });
       return true;
     } catch {
       getAuthClient().clearTokens();
+      clearCachedEmail();
       set({ hasBootstrapped: true, isAuthenticated: false, email: null, isLoading: false });
       return false;
     }
@@ -51,17 +165,20 @@ export const useAuthStore = create<AuthState>((set) => ({
     set({ isLoading: true });
 
     try {
-      await getAuthClient().register(email, password, displayName);
-      set({ hasBootstrapped: true, isAuthenticated: true, email, isLoading: false });
+      const result = await getAuthClient().register(email, password, displayName);
+      setCachedEmail(result.user.email);
+      set({ hasBootstrapped: true, isAuthenticated: true, email: result.user.email, isLoading: false });
       return true;
     } catch {
       getAuthClient().clearTokens();
+      clearCachedEmail();
       set({ hasBootstrapped: true, isAuthenticated: false, email: null, isLoading: false });
       return false;
     }
   },
   signOut() {
     getAuthClient().clearTokens();
+    clearCachedEmail();
     set({ hasBootstrapped: true, isAuthenticated: false, email: null, isLoading: false });
   },
 }));