diff --git a/src/lib/client/stores/auth.svelte.ts b/src/lib/client/stores/auth.svelte.ts
index a459b2d..a623949 100644
--- a/src/lib/client/stores/auth.svelte.ts
+++ b/src/lib/client/stores/auth.svelte.ts
@@ -187,14 +187,31 @@ async function register(
   }
 }
 
-function logout(): void {
+async function logout(): Promise<void> {
   state.user = null;
   state.credits = null;
   saveCachedAuth(null, null);
   setActiveUserId(null);
-  // Clear local session cookie by setting expired
-  document.cookie = 'graphini_session=; Path=/; Max-Age=0';
-  window.location.href = '/api/auth/logout';
+
+  // POST clears both graphini_session and graphini_guest_id server-side, then
+  // 302s to /. We don't follow that redirect via fetch (browsers won't apply
+  // its Set-Cookie to the document anyway when fetch follows redirects), so
+  // we read the response and force-navigate to / ourselves below. The
+  // Set-Cookie on the POST response is what actually removes the cookies.
+  //
+  // The earlier `window.location.href = '/api/auth/logout'` issued a GET,
+  // which routes to magnova-auth's federated signout — wrong for guests
+  // (they have no magnova session) and unnecessary for password users.
+  try {
+    await fetch('/api/auth/logout', {
+      method: 'POST',
+      credentials: 'include',
+      redirect: 'manual'
+    });
+  } catch {
+    /* non-fatal — client state is already cleared and we force-reload below. */
+  }
+  window.location.href = '/';
 }
 
 async function refreshCredits(): Promise<void> {
diff --git a/src/routes/api/auth/logout/+server.ts b/src/routes/api/auth/logout/+server.ts
index 2d6ef7f..c9d8e91 100644
--- a/src/routes/api/auth/logout/+server.ts
+++ b/src/routes/api/auth/logout/+server.ts
@@ -1,20 +1,22 @@
 import { redirect } from '@sveltejs/kit';
 import type { RequestHandler } from './$types';
-import { clearLocalSessionCookie, getSignoutUrl } from '$lib/server/auth';
+import { clearGuestCookieHeader, clearLocalSessionCookie, getSignoutUrl } from '$lib/server/auth';
 
 export const GET: RequestHandler = async () => {
-  // Clear local session cookie, then redirect to magnova-auth signout
+  // Federated (magnova-auth) signout flow. Reserved for OAuth users who
+  // want their upstream session terminated too. Local clients should use
+  // POST so guests and password-login users don't get bounced through an
+  // external auth provider that has no session for them.
   throw redirect(302, getSignoutUrl());
 };
 
 export const POST: RequestHandler = async ({ url }) => {
-  // Local logout — clear graphini_session cookie and redirect to home
+  // Local logout — clears both the password-session cookie and the guest
+  // cookie. Either may be present (or both, if a guest was migrated into
+  // a real account mid-session); clearing both is idempotent.
   const secureCookie = url.protocol === 'https:';
-  return new Response(null, {
-    status: 302,
-    headers: {
-      'Set-Cookie': clearLocalSessionCookie(secureCookie),
-      Location: '/'
-    }
-  });
+  const headers = new Headers({ Location: '/' });
+  headers.append('Set-Cookie', clearLocalSessionCookie(secureCookie));
+  headers.append('Set-Cookie', clearGuestCookieHeader(secureCookie));
+  return new Response(null, { status: 302, headers });
 };