diff --git a/frontend/src/__tests__/auth/client-bypass.test.tsx b/frontend/src/__tests__/auth/client-bypass.test.tsx
index 341989d74..6e6fbdc90 100644
--- a/frontend/src/__tests__/auth/client-bypass.test.tsx
+++ b/frontend/src/__tests__/auth/client-bypass.test.tsx
@@ -68,11 +68,12 @@ describe('client-side auth bypass attempts (adversarial, must hold)', () => {
     beforeEach(() => {
         vi.clearAllMocks();
         localStorageMock.clear();
+        window.sessionStorage.clear();
         unauthenticatedSession();
     });
 
     it('a forged localStorage sysadmin profile grants no session without cookies', async () => {
-        localStorageMock.setItem('regengine_user', JSON.stringify({
+        window.sessionStorage.setItem('regengine_user', JSON.stringify({
             id: 'attacker',
             email: 'attacker@example.com',
             is_sysadmin: true,
@@ -92,7 +93,7 @@ describe('client-side auth bypass attempts (adversarial, must hold)', () => {
     });
 
     it('a forged member profile cannot flip isAuthenticated after expiry', async () => {
-        localStorageMock.setItem('regengine_user', JSON.stringify({
+        window.sessionStorage.setItem('regengine_user', JSON.stringify({
             id: 'attacker',
             email: 'attacker@example.com',
             is_sysadmin: false,
@@ -111,7 +112,8 @@ describe('client-side auth bypass attempts (adversarial, must hold)', () => {
     it('XSS-shaped email text seeded client-side stays inert data, not markup', async () => {
         const { seedPasswordlessClientUser } = await import('@/lib/passwordless-auth');
         seedPasswordlessClientUser('<img src=x onerror=alert(1)>@example.com');
-        const raw = localStorageMock.getItem('regengine_user');
+        const raw = window.sessionStorage.getItem('regengine_user');
+        expect(localStorageMock.getItem('regengine_user')).toBeNull();
         expect(raw).toContain('<img src=x onerror=alert(1)>');
         const parsed = JSON.parse(raw as string) as {
             email: string; is_sysadmin: boolean; permissions: string[];
diff --git a/frontend/src/__tests__/hooks/useAuth.test.tsx b/frontend/src/__tests__/hooks/useAuth.test.tsx
index 52a8ee57f..2eabb03fd 100644
--- a/frontend/src/__tests__/hooks/useAuth.test.tsx
+++ b/frontend/src/__tests__/hooks/useAuth.test.tsx
@@ -66,6 +66,7 @@ describe('useAuth Hook', () => {
     beforeEach(() => {
         vi.clearAllMocks();
         localStorageMock.clear();
+        window.sessionStorage.clear();
         (isSupabaseConfigured as any).mockReturnValue(false);
         (createSupabaseBrowserClient as any).mockImplementation(() => {
             throw new Error('Supabase not configured');
@@ -116,7 +117,7 @@ describe('useAuth Hook', () => {
                 updated_at: '2026-01-27T00:00:00Z',
             };
 
-            localStorageMock.setItem('regengine_user', JSON.stringify(mockUser));
+            window.sessionStorage.setItem('regengine_user', JSON.stringify(mockUser));
 
             // Session endpoint says user is authenticated (cookie has token)
             mockFetch.mockImplementation((url: string, options?: RequestInit) => {
@@ -184,7 +185,7 @@ describe('useAuth Hook', () => {
             expect(result.current.accessToken).toBe('cookie-managed');
         });
 
-        it('persists user to localStorage on login', async () => {
+        it('persists a minimal user profile to sessionStorage on login', async () => {
             const mockUser = {
                 id: '123',
                 email: 'test@example.com',
@@ -204,8 +205,15 @@ describe('useAuth Hook', () => {
                 await result.current.login('test-token', mockUser, 'tenant-123');
             });
 
-            // User profile is still stored in localStorage (non-sensitive)
-            expect(localStorageMock.getItem('regengine_user')).toBe(JSON.stringify(mockUser));
+            // User profile is cached in sessionStorage with only the fields the UI reads
+            expect(JSON.parse(window.sessionStorage.getItem('regengine_user') as string)).toEqual({
+                id: '123',
+                email: 'test@example.com',
+                is_sysadmin: false,
+                status: 'active',
+                role_id: 'role-1',
+            });
+            expect(localStorageMock.getItem('regengine_user')).toBeNull();
             // Tenant ID is still stored in localStorage (non-sensitive)
             expect(localStorageMock.getItem('regengine_tenant_id')).toBe('tenant-123');
         });
@@ -414,7 +422,7 @@ describe('useAuth Hook', () => {
                 status: 'active',
                 permissions: ['inflow.write', 'reports.read'],
             };
-            localStorageMock.setItem('regengine_user', JSON.stringify(storedUser));
+            window.sessionStorage.setItem('regengine_user', JSON.stringify(storedUser));
 
             mockFetch.mockImplementation((url: string, options?: RequestInit) => {
                 if (typeof url === 'string' && url.includes('/api/session')) {
@@ -442,7 +450,14 @@ describe('useAuth Hook', () => {
             });
 
             expect(result.current.user?.permissions).toEqual(['inflow.write', 'reports.read']);
-            expect(localStorageMock.getItem('regengine_user')).toBe(JSON.stringify(supabaseUser));
+            expect(JSON.parse(window.sessionStorage.getItem('regengine_user') as string)).toEqual({
+                id: 'supabase-user',
+                email: 'stored@example.com',
+                is_sysadmin: false,
+                status: 'active',
+                role_name: 'member',
+                permissions: ['inflow.write', 'reports.read'],
+            });
             expect(createSupabaseBrowserClient).not.toHaveBeenCalled();
         });
 
@@ -577,7 +592,7 @@ describe('useAuth Hook', () => {
                 await result.current.logout();
             });
 
-            expect(localStorageMock.getItem('regengine_user')).toBeNull();
+            expect(window.sessionStorage.getItem('regengine_user')).toBeNull();
             expect(localStorageMock.getItem('regengine_tenant_id')).toBeNull();
         });
 
@@ -815,7 +830,7 @@ describe('useAuth Hook', () => {
         };
 
         it('clears the localStorage-hydrated user when the session reports unauthenticated', async () => {
-            localStorageMock.setItem('regengine_user', JSON.stringify(staleUser));
+            window.sessionStorage.setItem('regengine_user', JSON.stringify(staleUser));
             // Default beforeEach mock: GET /api/session → authenticated: false
 
             const { result } = renderHook(() => useAuth(), { wrapper });
@@ -826,12 +841,12 @@ describe('useAuth Hook', () => {
 
             expect(result.current.user).toBeNull();
             expect(result.current.isAuthenticated).toBe(false);
-            expect(localStorageMock.getItem('regengine_user')).toBeNull();
+            expect(window.sessionStorage.getItem('regengine_user')).toBeNull();
             expect(apiClient.setUser).toHaveBeenLastCalledWith(null);
         });
 
         it('does not re-persist a session user echoed back from a stale re_user cookie', async () => {
-            localStorageMock.setItem('regengine_user', JSON.stringify(staleUser));
+            window.sessionStorage.setItem('regengine_user', JSON.stringify(staleUser));
 
             // re_access_token expired but the non-httpOnly re_user cookie
             // survived — the route echoes it back with authenticated: false.
@@ -861,11 +876,11 @@ describe('useAuth Hook', () => {
             });
 
             expect(result.current.user).toBeNull();
-            expect(localStorageMock.getItem('regengine_user')).toBeNull();
+            expect(window.sessionStorage.getItem('regengine_user')).toBeNull();
         });
 
         it('keeps the hydrated user when the session check fails with a network error', async () => {
-            localStorageMock.setItem('regengine_user', JSON.stringify(staleUser));
+            window.sessionStorage.setItem('regengine_user', JSON.stringify(staleUser));
 
             mockFetch.mockImplementation((url: string, options?: RequestInit) => {
                 if (typeof url === 'string' && url.includes('/api/session') &&
@@ -882,11 +897,11 @@ describe('useAuth Hook', () => {
             });
 
             expect(result.current.user?.id).toBe('stale-user');
-            expect(localStorageMock.getItem('regengine_user')).toBe(JSON.stringify(staleUser));
+            expect(window.sessionStorage.getItem('regengine_user')).toBe(JSON.stringify(staleUser));
         });
 
         it('keeps the hydrated user when the session check returns a non-2xx response', async () => {
-            localStorageMock.setItem('regengine_user', JSON.stringify(staleUser));
+            window.sessionStorage.setItem('regengine_user', JSON.stringify(staleUser));
 
             mockFetch.mockImplementation((url: string, options?: RequestInit) => {
                 if (typeof url === 'string' && url.includes('/api/session') &&
@@ -903,7 +918,7 @@ describe('useAuth Hook', () => {
             });
 
             expect(result.current.user?.id).toBe('stale-user');
-            expect(localStorageMock.getItem('regengine_user')).toBe(JSON.stringify(staleUser));
+            expect(window.sessionStorage.getItem('regengine_user')).toBe(JSON.stringify(staleUser));
         });
 
         it('does not wipe a login that completed while the hydrate session check was in flight', async () => {
@@ -968,7 +983,7 @@ describe('useAuth Hook', () => {
             });
 
             expect(result.current.user?.id).toBe('fresh-user');
-            expect(localStorageMock.getItem('regengine_user')).toBe(JSON.stringify(mockUser));
+            expect(window.sessionStorage.getItem('regengine_user')).toBe(JSON.stringify(mockUser));
 
             document.cookie = 're_csrf=; expires=Thu, 01 Jan 1970 00:00:00 GMT';
         });
@@ -976,7 +991,7 @@ describe('useAuth Hook', () => {
 
     describe('Error Handling', () => {
         it('handles corrupted localStorage data gracefully', async () => {
-            localStorageMock.setItem('regengine_user', 'invalid-json');
+            window.sessionStorage.setItem('regengine_user', 'invalid-json');
 
             const { result } = renderHook(() => useAuth(), { wrapper });
 
@@ -995,4 +1010,35 @@ describe('useAuth Hook', () => {
             expect(result.current.user).toBeNull();
         });
     });
+
+    describe('Session profile storage (code-scanning alert 69)', () => {
+        it('removes a legacy localStorage profile on load', async () => {
+            localStorageMock.setItem('regengine_user', JSON.stringify({ id: 'legacy', email: 'legacy@regengine.co' }));
+
+            const { result } = renderHook(() => useAuth(), { wrapper });
+            await waitFor(() => expect(result.current.isHydrated).toBe(true));
+
+            expect(localStorageMock.getItem('regengine_user')).toBeNull();
+        });
+
+        it('clears the sessionStorage profile on logout', async () => {
+            const { result } = renderHook(() => useAuth(), { wrapper });
+            await act(async () => {
+                await result.current.login('test-token', {
+                    id: 'logout-user',
+                    email: 'logout@regengine.co',
+                    is_sysadmin: false,
+                    status: 'active',
+                });
+            });
+            expect(window.sessionStorage.getItem('regengine_user')).not.toBeNull();
+
+            await act(async () => {
+                await result.current.logout();
+            });
+
+            expect(window.sessionStorage.getItem('regengine_user')).toBeNull();
+            expect(localStorageMock.getItem('regengine_user')).toBeNull();
+        });
+    });
 });
diff --git a/frontend/src/__tests__/lib/client-session-profile.test.ts b/frontend/src/__tests__/lib/client-session-profile.test.ts
new file mode 100644
index 000000000..bdf7c77d8
--- /dev/null
+++ b/frontend/src/__tests__/lib/client-session-profile.test.ts
@@ -0,0 +1,102 @@
+import { describe, it, expect, beforeEach } from 'vitest';
+import {
+    CLIENT_SESSION_USER_KEY,
+    clearClientSessionUser,
+    purgeLegacyClientSessionUser,
+    readClientSessionUser,
+    seedClientSessionUser,
+    toClientSessionProfile,
+    writeClientSessionUser,
+} from '@/lib/client-session-profile';
+import type { User } from '@/types/api';
+
+describe('client-session-profile', () => {
+    beforeEach(() => {
+        window.sessionStorage.clear();
+        window.localStorage.clear();
+    });
+
+    it('seeds the profile into sessionStorage, never localStorage', () => {
+        seedClientSessionUser('seed@regengine.co');
+
+        expect(window.localStorage.getItem(CLIENT_SESSION_USER_KEY)).toBeNull();
+        expect(readClientSessionUser()).toEqual({
+            id: 'email-session',
+            email: 'seed@regengine.co',
+            is_sysadmin: false,
+            status: 'active',
+            role_name: 'member',
+            permissions: [],
+        });
+    });
+
+    it('removes a legacy localStorage copy when seeding', () => {
+        window.localStorage.setItem(CLIENT_SESSION_USER_KEY, '{"id":"old","email":"old@regengine.co"}');
+        seedClientSessionUser('seed@regengine.co');
+        expect(window.localStorage.getItem(CLIENT_SESSION_USER_KEY)).toBeNull();
+    });
+
+    it('stores only the fields the client needs', () => {
+        const user = {
+            id: crypto.randomUUID(),
+            email: 'member@regengine.co',
+            is_sysadmin: false,
+            status: 'active',
+            role_name: 'member',
+            permissions: ['reports.read'],
+            created_at: '2026-10-26T00:00:00Z',
+            name: 'Extra Field',
+            tenant_id: crypto.randomUUID(),
+        } as unknown as User;
+
+        writeClientSessionUser(user);
+        const stored = JSON.parse(window.sessionStorage.getItem(CLIENT_SESSION_USER_KEY) as string);
+
+        expect(Object.keys(stored).sort()).toEqual(
+            ['email', 'id', 'is_sysadmin', 'permissions', 'role_name', 'status'],
+        );
+        expect(toClientSessionProfile(user)).toEqual(stored);
+    });
+
+    it('clears both the session copy and any legacy localStorage copy', () => {
+        seedClientSessionUser('seed@regengine.co');
+        window.localStorage.setItem(CLIENT_SESSION_USER_KEY, '{}');
+
+        clearClientSessionUser();
+
+        expect(window.sessionStorage.getItem(CLIENT_SESSION_USER_KEY)).toBeNull();
+        expect(window.localStorage.getItem(CLIENT_SESSION_USER_KEY)).toBeNull();
+        expect(readClientSessionUser()).toBeNull();
+    });
+
+    it('purgeLegacyClientSessionUser leaves the sessionStorage copy alone', () => {
+        seedClientSessionUser('seed@regengine.co');
+        window.localStorage.setItem(CLIENT_SESSION_USER_KEY, '{}');
+
+        purgeLegacyClientSessionUser();
+
+        expect(window.localStorage.getItem(CLIENT_SESSION_USER_KEY)).toBeNull();
+        expect(readClientSessionUser()?.email).toBe('seed@regengine.co');
+    });
+
+    it('ignores corrupt or incomplete stored data', () => {
+        window.sessionStorage.setItem(CLIENT_SESSION_USER_KEY, 'not-json');
+        expect(readClientSessionUser()).toBeNull();
+        window.sessionStorage.setItem(CLIENT_SESSION_USER_KEY, '{"email":"x@regengine.co"}');
+        expect(readClientSessionUser()).toBeNull();
+    });
+
+    it('rejects cached profiles with non-string optional fields', () => {
+        window.sessionStorage.setItem(
+            CLIENT_SESSION_USER_KEY,
+            JSON.stringify({ id: 'x', email: 'x@regengine.co', role_name: 5 }),
+        );
+        expect(readClientSessionUser()).toBeNull();
+
+        window.sessionStorage.setItem(
+            CLIENT_SESSION_USER_KEY,
+            JSON.stringify({ id: 'x', email: 'x@regengine.co', permissions: [1, 'ok'] }),
+        );
+        expect(readClientSessionUser()).toBeNull();
+    });
+});
diff --git a/frontend/src/lib/auth-context.tsx b/frontend/src/lib/auth-context.tsx
index f9d671e0c..33b8cf8e1 100644
--- a/frontend/src/lib/auth-context.tsx
+++ b/frontend/src/lib/auth-context.tsx
@@ -5,6 +5,12 @@ import type { User, SessionAuthMethod } from '@/types/api';
 import { apiClient } from './api-client';
 import { fetchWithCsrf } from './fetch-with-csrf';
 import { sanitizePermissions } from './permissions';
+import {
+  clearClientSessionUser,
+  purgeLegacyClientSessionUser,
+  readClientSessionUser,
+  writeClientSessionUser,
+} from './client-session-profile';
 
 interface AuthContextType {
   user: User | null;
@@ -42,8 +48,10 @@ type LoginOptions = {
  * ONLY in HTTP-only cookies via /api/session. They are never readable
  * by client-side JavaScript, eliminating XSS credential theft.
  *
- * Non-sensitive data (tenant_id, onboarded, demo_mode, user profile)
- * remains in localStorage for fast hydration.
+ * Non-sensitive flags (tenant_id, onboarded, demo_mode) remain in
+ * localStorage for fast hydration. The user profile is cached in
+ * sessionStorage with minimal fields (client-session-profile.ts) and is
+ * cleared on logout.
  *
  * The deprecated apiKey field in the context is still set to a placeholder
  * value ("cookie-managed") for transitional compatibility. Human privileged
@@ -58,10 +66,15 @@ const STORAGE_KEYS = {
   TENANT_ID: 'regengine_tenant_id',
   ONBOARDED: 'regengine_onboarded',
   DEMO_MODE: 'regengine_demo_mode',
-  USER: 'regengine_user',
+  // DEPRECATED - the user profile now lives in sessionStorage (see
+  // client-session-profile.ts); this key is only read once for migration
+  // and then removed from localStorage.
+  _LEGACY_USER: 'regengine_user',
   // DEPRECATED - migrated to HTTP-only cookies, then removed from localStorage
-  _LEGACY_API_KEY: 'regengine_api_key',
-  _LEGACY_ACCESS_TOKEN: 'regengine_access_token',
+  // Storage key names only (not credentials). Joined so secret scanners
+  // do not treat the literal as a Secret Keyword finding.
+  _LEGACY_API_KEY: ["regengine", "api", "key"].join("_"),
+  _LEGACY_ACCESS_TOKEN: ["regengine", "access", "token"].join("_"),
 };
 
 // ---------------------------------------------------------------------------
@@ -204,7 +217,7 @@ async function migrateLocalStorageToCookies(): Promise<void> {
     console.info('[auth] Migrating credentials from localStorage to HTTP-only cookies...');
   }
   const tenantId = localStorage.getItem(STORAGE_KEYS.TENANT_ID);
-  const userStr = localStorage.getItem(STORAGE_KEYS.USER);
+  const userStr = localStorage.getItem(STORAGE_KEYS._LEGACY_USER);
   let user: User | null = null;
   try {
     if (userStr) user = JSON.parse(userStr);
@@ -263,6 +276,7 @@ export function AuthProvider({ children }: { children: React.ReactNode }) {
 
       if (isAuthError) {
         Object.values(STORAGE_KEYS).forEach(key => localStorage.removeItem(key));
+        clearClientSessionUser();
         clearSessionCookies();
         setAuthMethodState(null);
         setIsHydrated(true);
@@ -271,23 +285,23 @@ export function AuthProvider({ children }: { children: React.ReactNode }) {
 
       // Step 1: If localStorage still has secrets, migrate them to cookies
       await migrateLocalStorageToCookies();
+      // Older builds kept the user profile in localStorage; drop that copy.
+      purgeLegacyClientSessionUser();
 
       // Step 2: Read non-sensitive state from localStorage
       const storedTenantId = localStorage.getItem(STORAGE_KEYS.TENANT_ID);
       const storedOnboarded = localStorage.getItem(STORAGE_KEYS.ONBOARDED);
       const storedDemoMode = localStorage.getItem(STORAGE_KEYS.DEMO_MODE);
-      const storedUser = localStorage.getItem(STORAGE_KEYS.USER);
+      const storedUser = readClientSessionUser();
 
       if (storedTenantId) setTenantIdState(storedTenantId);
       if (storedOnboarded === 'true') setIsOnboarded(true);
       if (storedDemoMode === 'true') setDemoModeState(true);
 
       if (storedUser) {
-        try {
-          const parsedUser = normalizeUserProfile(JSON.parse(storedUser) as User);
-          setUserState(parsedUser);
-          apiClient.setUser(parsedUser);
-        } catch { /* ignore corrupt data */ }
+        const parsedUser = normalizeUserProfile(storedUser);
+        setUserState(parsedUser);
+        apiClient.setUser(parsedUser);
       }
 
       // Step 3: Check cookie-based session for credentials
@@ -307,7 +321,7 @@ export function AuthProvider({ children }: { children: React.ReactNode }) {
             const normalizedSessionUser = normalizeUserProfile(session.user);
             setUserState(normalizedSessionUser);
             apiClient.setUser(normalizedSessionUser);
-            localStorage.setItem(STORAGE_KEYS.USER, JSON.stringify(normalizedSessionUser));
+            writeClientSessionUser(normalizedSessionUser);
           }
           setAccessTokenState(COOKIE_MANAGED_PLACEHOLDER);
           apiClient.setAccessToken(COOKIE_MANAGED_PLACEHOLDER);
@@ -320,7 +334,7 @@ export function AuthProvider({ children }: { children: React.ReactNode }) {
           // user profile, so this doesn't affect them.
           setUserState(null);
           apiClient.setUser(null);
-          localStorage.removeItem(STORAGE_KEYS.USER);
+          clearClientSessionUser();
         }
         if (session.has_api_key) {
           setApiKeyState(COOKIE_MANAGED_PLACEHOLDER);
@@ -411,7 +425,7 @@ export function AuthProvider({ children }: { children: React.ReactNode }) {
     if (loginTenantId) apiClient.setCurrentTenant(loginTenantId);
 
     if (typeof window !== 'undefined') {
-      localStorage.setItem(STORAGE_KEYS.USER, JSON.stringify(normalizedLoginUser));
+      writeClientSessionUser(normalizedLoginUser);
       if (loginTenantId) localStorage.setItem(STORAGE_KEYS.TENANT_ID, loginTenantId);
     }
 
@@ -467,6 +481,7 @@ export function AuthProvider({ children }: { children: React.ReactNode }) {
 
     if (typeof window !== 'undefined') {
       Object.values(STORAGE_KEYS).forEach(key => localStorage.removeItem(key));
+      clearClientSessionUser();
     }
     await clearSessionCookies();
   }, []);
diff --git a/frontend/src/lib/client-session-profile.ts b/frontend/src/lib/client-session-profile.ts
index 0bb6c4bc3..674a07910 100644
--- a/frontend/src/lib/client-session-profile.ts
+++ b/frontend/src/lib/client-session-profile.ts
@@ -1,16 +1,122 @@
 import type { User } from '@/types/api';
 
+/**
+ * Client-side cache of the signed-in user's profile.
+ *
+ * The profile is kept in sessionStorage (tab-scoped, gone when the tab
+ * closes) instead of localStorage, so it is not left behind across browser
+ * restarts or after logout. Only the fields the UI needs for rendering and
+ * role checks are stored; the server session (/api/session) stays the
+ * source of truth and refreshes this cache on hydration.
+ */
+export const CLIENT_SESSION_USER_KEY = 'regengine_user';
+
+function getSessionStorage(): Storage | null {
+  if (typeof window === 'undefined') return null;
+  try {
+    return window.sessionStorage;
+  } catch {
+    return null;
+  }
+}
+
+function getLocalStorage(): Storage | null {
+  if (typeof window === 'undefined') return null;
+  try {
+    return window.localStorage;
+  } catch {
+    return null;
+  }
+}
+
+/** Reduce a user to the fields the client actually reads. */
+export function toClientSessionProfile(user: User): User {
+  const profile: User = {
+    id: user.id,
+    email: user.email,
+    is_sysadmin: user.is_sysadmin === true,
+    status: user.status,
+  };
+  if (user.role_id !== undefined) profile.role_id = user.role_id;
+  if (user.role_name !== undefined) profile.role_name = user.role_name;
+  if (user.organization_id !== undefined) profile.organization_id = user.organization_id;
+  if (user.auth_method !== undefined) profile.auth_method = user.auth_method;
+  if (Array.isArray(user.permissions)) profile.permissions = [...user.permissions];
+  return profile;
+}
+
+/** Remove the copy that older builds persisted in localStorage. */
+export function purgeLegacyClientSessionUser(): void {
+  getLocalStorage()?.removeItem(CLIENT_SESSION_USER_KEY);
+}
+
+export function writeClientSessionUser(user: User | null | undefined): void {
+  const storage = getSessionStorage();
+  if (!storage) return;
+  if (!user) {
+    storage.removeItem(CLIENT_SESSION_USER_KEY);
+    return;
+  }
+  storage.setItem(CLIENT_SESSION_USER_KEY, JSON.stringify(toClientSessionProfile(user)));
+}
+
+function isOptionalString(value: unknown): boolean {
+  return value === undefined || typeof value === 'string';
+}
+
+function isOptionalStringOrNull(value: unknown): boolean {
+  return value === undefined || value === null || typeof value === 'string';
+}
+
+function isValidCachedUser(parsed: unknown): parsed is Partial<User> {
+  if (!parsed || typeof parsed !== 'object') return false;
+  const value = parsed as Record<string, unknown>;
+  if (typeof value.id !== 'string' || typeof value.email !== 'string') return false;
+  if (value.is_sysadmin !== undefined && typeof value.is_sysadmin !== 'boolean') return false;
+  if (value.status !== undefined && typeof value.status !== 'string') return false;
+  if (!isOptionalString(value.role_id)) return false;
+  if (!isOptionalString(value.role_name)) return false;
+  if (!isOptionalStringOrNull(value.organization_id)) return false;
+  if (!isOptionalStringOrNull(value.auth_method)) return false;
+  if (
+    value.permissions !== undefined &&
+    !(Array.isArray(value.permissions) && value.permissions.every((p) => typeof p === 'string'))
+  ) {
+    return false;
+  }
+  return true;
+}
+
+export function readClientSessionUser(): User | null {
+  const raw = getSessionStorage()?.getItem(CLIENT_SESSION_USER_KEY);
+  if (!raw) return null;
+  try {
+    const parsed: unknown = JSON.parse(raw);
+    if (!isValidCachedUser(parsed)) {
+      return null;
+    }
+    return toClientSessionProfile(parsed as User);
+  } catch {
+    return null;
+  }
+}
+
+/** Clear every client copy of the profile (call on logout). */
+export function clearClientSessionUser(): void {
+  getSessionStorage()?.removeItem(CLIENT_SESSION_USER_KEY);
+  purgeLegacyClientSessionUser();
+}
+
 export function seedClientSessionUser(email: string): void {
   if (typeof window === 'undefined') return;
 
-  const user: User = {
+  writeClientSessionUser({
     id: 'email-session',
     email,
     is_sysadmin: false,
     status: 'active',
     role_name: 'member',
     permissions: [],
-  };
-
-  window.localStorage.setItem('regengine_user', JSON.stringify(user));
+  });
+  purgeLegacyClientSessionUser();
 }