diff --git a/src/stores/__tests__/calendar-store.test.ts b/src/stores/__tests__/calendar-store.test.ts
index 6f23568b..f24db0f1 100644
--- a/src/stores/__tests__/calendar-store.test.ts
+++ b/src/stores/__tests__/calendar-store.test.ts
@@ -20,6 +20,7 @@ vi.mock('@react-native-async-storage/async-storage', () => ({
 vi.mock('../../api/jmap-client', () => ({
   jmapClient: {
     accountId: 'acc-1',
+    isConnected: true,
   },
 }));
 
diff --git a/src/stores/__tests__/contacts-store.test.ts b/src/stores/__tests__/contacts-store.test.ts
index cc63f4cd..8390926f 100644
--- a/src/stores/__tests__/contacts-store.test.ts
+++ b/src/stores/__tests__/contacts-store.test.ts
@@ -20,6 +20,7 @@ vi.mock('@react-native-async-storage/async-storage', () => ({
 vi.mock('../../api/jmap-client', () => ({
   jmapClient: {
     accountId: 'acc-1',
+    isConnected: true,
   },
 }));
 
diff --git a/src/stores/__tests__/email-store.test.ts b/src/stores/__tests__/email-store.test.ts
index 4417b167..5f202a43 100644
--- a/src/stores/__tests__/email-store.test.ts
+++ b/src/stores/__tests__/email-store.test.ts
@@ -17,7 +17,18 @@ vi.mock('../../api/email', () => ({
 // trip on react-native's Flow-typed entrypoint under vitest. The store only
 // reads archiveMode in archiveEmail, so a minimal stub is enough.
 vi.mock('../settings-store', () => ({
-  useSettingsStore: { getState: () => ({ archiveMode: 'single' }) },
+  useSettingsStore: { getState: () => ({ archiveMode: 'single', emailsPerPage: 25 }) },
+}));
+
+// email-store now early-returns from fetch actions when jmapClient.isConnected
+// is false (cold-start guard). The tests exercise those actions, so present
+// a connected stub.
+vi.mock('../../api/jmap-client', () => ({
+  jmapClient: {
+    isConnected: true,
+    accountId: 'acc-1',
+    currentSession: { apiUrl: 'https://mail.example.com/jmap/' },
+  },
 }));
 
 import * as emailApi from '../../api/email';
diff --git a/src/stores/auth-store.ts b/src/stores/auth-store.ts
index b979728f..86823a95 100644
--- a/src/stores/auth-store.ts
+++ b/src/stores/auth-store.ts
@@ -225,17 +225,42 @@ export const useAuthStore = create<AuthState>((set, get) => ({
 
     set({ isLoading: true, error: null });
 
-    jmapClient.reset();
-    resetFeatureStores();
-
-    const ok = await jmapClient.loadAccount(accountId);
-    if (!ok) {
-      // Credentials missing - evict stale entry and surface error
-      accountStore.removeAccount(accountId);
-      set({ isLoading: false, error: 'Session expired for this account' });
+    // Load the new account's session BEFORE clearing jmapClient or feature
+    // stores. The previous order (reset → resetFeatureStores → loadAccount)
+    // left jmapClient with no accountId during the loadAccount await, and
+    // any fetch fired by a screen effect reacting to the emptied stores
+    // (e.g. EmailListScreen retrying fetchMailboxes when mailboxes goes to
+    // []) threw "Not authenticated - call connect() first". loadAccount
+    // overwrites credentials/session/_accountId itself, so the pre-reset
+    // is unnecessary.
+    try {
+      const ok = await jmapClient.loadAccount(accountId);
+      if (!ok) {
+        // Credentials missing - evict stale entry and surface error
+        accountStore.removeAccount(accountId);
+        set({ isLoading: false, error: 'Session expired for this account' });
+        return;
+      }
+    } catch (err) {
+      if (err instanceof AuthenticationError) {
+        await jmapClient.clearAccountCredentials(accountId).catch(() => undefined);
+        accountStore.removeAccount(accountId);
+        set({ isLoading: false, error: 'Session expired for this account' });
+        return;
+      }
+      // NetworkError or anything else - keep the previous active account
+      // intact instead of stranding the user on a half-switched state.
+      set({
+        isLoading: false,
+        error: err instanceof Error ? err.message : 'Failed to switch account',
+      });
       return;
     }
 
+    // Session is in place under the new account. Safe now to wipe the
+    // previous account's cached feature data; the refetch below repopulates.
+    resetFeatureStores();
+
     accountStore.setActiveAccount(accountId);
     accountStore.updateAccount(accountId, {
       isConnected: true,
diff --git a/src/stores/calendar-store.ts b/src/stores/calendar-store.ts
index 375b8fb9..2490cd8d 100644
--- a/src/stores/calendar-store.ts
+++ b/src/stores/calendar-store.ts
@@ -89,6 +89,11 @@ export const useCalendarStore = create<CalendarState>()(
   },
 
   fetchCalendars: async () => {
+    // CalendarScreen fires this on mount; on cold start that happens before
+    // restoreSession has connected jmapClient. Bail rather than surfacing
+    // a "Not authenticated" error - the refetch driven by the auth-store
+    // will run this again once the session is live.
+    if (!jmapClient.isConnected) return;
     try {
       const calendars = (await fetchCalendars()) ?? [];
       set({ calendars });
@@ -98,6 +103,7 @@ export const useCalendarStore = create<CalendarState>()(
   },
 
   fetchEvents: async (calendarIds, after, before) => {
+    if (!jmapClient.isConnected) return;
     set({ loading: true, error: null });
     try {
       const ids = (await queryEvents(calendarIds, after, before)) ?? [];
@@ -142,6 +148,7 @@ export const useCalendarStore = create<CalendarState>()(
   },
 
   handleStateChange: async (change) => {
+    if (!jmapClient.isConnected) return;
     const accountId = jmapClient.accountId;
     const accountChanges = change.changed?.[accountId];
     if (!accountChanges) return;
diff --git a/src/stores/contacts-store.ts b/src/stores/contacts-store.ts
index 16819857..47f72438 100644
--- a/src/stores/contacts-store.ts
+++ b/src/stores/contacts-store.ts
@@ -87,6 +87,10 @@ export const useContactsStore = create<ContactsState>()(
   },
 
   fetchAddressBooks: async () => {
+    // No-op until a JMAP session exists. ContactsScreen fires this from a
+    // mount-time useEffect, which on cold start runs before restoreSession
+    // has set up the client.
+    if (!jmapClient.isConnected) return;
     try {
       const addressBooks = (await fetchAddressBooks()) ?? [];
       set({ addressBooks });
@@ -96,6 +100,7 @@ export const useContactsStore = create<ContactsState>()(
   },
 
   fetchContacts: async (filter) => {
+    if (!jmapClient.isConnected) return;
     set({ loading: true, error: null });
     try {
       const ids = (await queryContacts(filter)) ?? [];
@@ -111,6 +116,7 @@ export const useContactsStore = create<ContactsState>()(
   },
 
   handleStateChange: async (change) => {
+    if (!jmapClient.isConnected) return;
     const accountId = jmapClient.accountId;
     const accountChanges = change.changed?.[accountId];
     if (!accountChanges) return;
diff --git a/src/stores/email-store.ts b/src/stores/email-store.ts
index 4a81b296..a7b25ea4 100644
--- a/src/stores/email-store.ts
+++ b/src/stores/email-store.ts
@@ -129,6 +129,13 @@ export const useEmailStore = create<EmailState>()(
   pendingUndo: null,
 
   fetchMailboxes: async () => {
+    // Skip silently when there's no live session. Screens fire this from
+    // mount-time useEffects, and on cold start App.tsx renders MainTabs
+    // before restoreSession() finishes; without this guard the underlying
+    // API call would throw "Not authenticated - call connect() first" and
+    // surface as a user-visible error before the real fetch (kicked off by
+    // refetchFeatureStores() once the session is live) replaces it.
+    if (!jmapClient.isConnected) return;
     try {
       const mailboxes = await fetchMailboxes();
       set({ mailboxes });
@@ -171,6 +178,15 @@ export const useEmailStore = create<EmailState>()(
       }
     }
 
+    // Stop here if there's no live session yet — the cached seed already
+    // gave the user something to look at, and the refetch driven by
+    // restoreSession() / switchAccount will run the network half once the
+    // client is connected.
+    if (!jmapClient.isConnected) {
+      set({ loading: false });
+      return;
+    }
+
     try {
       const filter = buildJmapFilter(mailboxId, '', {});
       const { ids, total } = await queryEmails(mailboxId, { limit, filter });
@@ -195,6 +211,7 @@ export const useEmailStore = create<EmailState>()(
   loadMoreEmails: async () => {
     const { currentMailboxId, emails, totalEmails, loading, searchQuery, filters } = get();
     if (!currentMailboxId || loading || emails.length >= totalEmails) return;
+    if (!jmapClient.isConnected) return;
 
     set({ loading: true });
     try {
@@ -215,6 +232,7 @@ export const useEmailStore = create<EmailState>()(
   refreshEmails: async () => {
     const { currentMailboxId, searchQuery, filters, emails: existing } = get();
     if (!currentMailboxId) return;
+    if (!jmapClient.isConnected) return;
     // Keep existing emails visible while refreshing - swap atomically once
     // the new list is ready so pull-to-refresh doesn't flash an empty list.
     set({ loading: true, error: null });