diff --git a/backend/Cargo.toml b/backend/Cargo.toml
index c091570..1209b66 100644
--- a/backend/Cargo.toml
+++ b/backend/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "mangalord"
-version = "0.34.0"
+version = "0.35.0"
 edition = "2021"
 default-run = "mangalord"
 
diff --git a/frontend/package.json b/frontend/package.json
index 159dad9..6a36df7 100644
--- a/frontend/package.json
+++ b/frontend/package.json
@@ -1,6 +1,6 @@
 {
   "name": "mangalord-frontend",
-  "version": "0.34.0",
+  "version": "0.35.0",
   "private": true,
   "type": "module",
   "scripts": {
diff --git a/frontend/src/lib/api/client.test.ts b/frontend/src/lib/api/client.test.ts
index 49e292c..417de75 100644
--- a/frontend/src/lib/api/client.test.ts
+++ b/frontend/src/lib/api/client.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect, vi, beforeEach, afterEach, type MockInstance } from 'vitest';
-import { ApiError, request } from './client';
+import { ApiError, request, setOn401Hook } from './client';
 import { getManga } from './mangas';
 
 describe('request error envelope parsing', () => {
@@ -73,3 +73,88 @@ describe('request error envelope parsing', () => {
         expect(err.code).toBe('http_error');
     });
 });
+
+describe('on401 hook', () => {
+    let fetchSpy: MockInstance<typeof globalThis.fetch>;
+
+    beforeEach(() => {
+        fetchSpy = vi.spyOn(globalThis, 'fetch');
+    });
+    afterEach(() => {
+        vi.restoreAllMocks();
+        // Critical: reset the module-level hook between tests so a
+        // hook installed by one test doesn't leak into the next.
+        setOn401Hook(null);
+    });
+
+    it('invokes the hook exactly once on a 401 response and re-throws', async () => {
+        const hook = vi.fn();
+        setOn401Hook(hook);
+        fetchSpy.mockResolvedValueOnce(
+            new Response(
+                JSON.stringify({ error: { code: 'unauthenticated', message: 'no auth' } }),
+                { status: 401, headers: { 'content-type': 'application/json' } }
+            )
+        );
+        await expect(getManga('x')).rejects.toMatchObject({
+            status: 401,
+            code: 'unauthenticated'
+        });
+        expect(hook).toHaveBeenCalledTimes(1);
+    });
+
+    it('does not invoke the hook on non-401 errors', async () => {
+        const hook = vi.fn();
+        setOn401Hook(hook);
+        fetchSpy.mockResolvedValueOnce(
+            new Response(
+                JSON.stringify({ error: { code: 'not_found', message: 'no' } }),
+                { status: 404, headers: { 'content-type': 'application/json' } }
+            )
+        );
+        await expect(getManga('x')).rejects.toMatchObject({ status: 404 });
+        expect(hook).not.toHaveBeenCalled();
+    });
+
+    it('does not invoke the hook on successful responses', async () => {
+        const hook = vi.fn();
+        setOn401Hook(hook);
+        fetchSpy.mockResolvedValueOnce(
+            new Response(
+                JSON.stringify({
+                    id: 'm1',
+                    title: 't',
+                    status: 'ongoing',
+                    alt_titles: [],
+                    description: null,
+                    cover_image_path: null,
+                    created_at: '2026-01-01T00:00:00Z',
+                    updated_at: '2026-01-01T00:00:00Z',
+                    authors: [],
+                    genres: [],
+                    tags: []
+                }),
+                { status: 200, headers: { 'content-type': 'application/json' } }
+            )
+        );
+        await getManga('m1');
+        expect(hook).not.toHaveBeenCalled();
+    });
+
+    it('swallows hook exceptions so the original ApiError still propagates', async () => {
+        const consoleSpy = vi.spyOn(console, 'error').mockImplementation(() => {});
+        setOn401Hook(() => {
+            throw new Error('hook boom');
+        });
+        fetchSpy.mockResolvedValueOnce(
+            new Response(
+                JSON.stringify({ error: { code: 'unauthenticated', message: 'x' } }),
+                { status: 401, headers: { 'content-type': 'application/json' } }
+            )
+        );
+        await expect(getManga('x')).rejects.toMatchObject({ status: 401 });
+        // The original ApiError won — the hook's panic was logged but
+        // didn't replace the API error.
+        expect(consoleSpy).toHaveBeenCalled();
+    });
+});
diff --git a/frontend/src/lib/api/client.ts b/frontend/src/lib/api/client.ts
index a272be7..6b690be 100644
--- a/frontend/src/lib/api/client.ts
+++ b/frontend/src/lib/api/client.ts
@@ -25,6 +25,21 @@ export class ApiError extends Error {
 
 type ErrorEnvelope = { error?: { code?: unknown; message?: unknown } };
 
+/**
+ * Optional hook fired the first moment `request()` observes a 401 on
+ * any endpoint. Used by the session store to clear the cached user
+ * when the server reports the session is no longer valid (expired
+ * cookie, rotated server-side, password changed on another device).
+ *
+ * Set to `null` (or `undefined`) to disable. Tests that don't want
+ * the side effect should leave it unset.
+ */
+let on401Hook: (() => void) | null = null;
+
+export function setOn401Hook(handler: (() => void) | null): void {
+    on401Hook = handler;
+}
+
 export async function request<T>(path: string, init?: RequestInit): Promise<T> {
     // Forward credentials (session cookie) explicitly so cross-origin
     // deployments — those configured via CORS_ALLOWED_ORIGINS — keep
@@ -54,6 +69,16 @@ export async function request<T>(path: string, init?: RequestInit): Promise<T> {
         } catch {
             // Body wasn't parseable; keep the http_error fallback.
         }
+        if (res.status === 401 && on401Hook) {
+            // Fire before throwing so the session store updates even
+            // if the caller swallows the ApiError (e.g. the *OrEmpty
+            // wrappers used by guest-rendering pages).
+            try {
+                on401Hook();
+            } catch (e) {
+                console.error('on401 hook threw:', e);
+            }
+        }
         throw new ApiError(res.status, code, message);
     }
     // Any empty body (not just 204) returns undefined — the manga-add
diff --git a/frontend/src/lib/session.svelte.ts b/frontend/src/lib/session.svelte.ts
index cd72d91..cdb13ff 100644
--- a/frontend/src/lib/session.svelte.ts
+++ b/frontend/src/lib/session.svelte.ts
@@ -3,7 +3,17 @@
 // Only mutated client-side (onMount / form submits) so the module-level
 // instance can't leak across SSR requests — SSR always renders the
 // `loaded === false` state, and the client refreshes after hydration.
+//
+// IMPORTANT: do not call any `api/*` helper from `+page.server.ts` /
+// `+layout.server.ts`. The `setOn401Hook` below is registered at
+// module load (gated on `browser`, so it only fires in the client
+// bundle), so a 401 from a server-side fetch would mutate this
+// module-level `session.user` across SvelteKit requests — a real
+// cross-request state leak. The `if (browser)` guard makes that
+// failure mode mechanical rather than convention-based.
 
+import { browser } from '$app/environment';
+import { setOn401Hook } from './api/client';
 import { me, type User } from './api/auth';
 
 class SessionStore {
@@ -31,3 +41,16 @@ class SessionStore {
 }
 
 export const session = new SessionStore();
+
+// When any backend call returns 401, drop the cached user. Before this
+// hook, the `*OrEmpty` wrappers silently returned empty pages on 401
+// — so a mid-session expiry left the UI rendering as "logged in but
+// no bookmarks/collections/etc." until the user manually reloaded.
+// With the hook the session.user reactive store flips to null on the
+// first 401, so the layout re-renders the login affordance.
+//
+// Gated on `browser` so it's only installed in the client bundle.
+// See the module-level comment above for the SSR rationale.
+if (browser) {
+    setOn401Hook(() => session.setUser(null));
+}