diff --git a/frontend/components/ToastProvider.tsx b/frontend/components/ToastProvider.tsx
index 62a96f5..36dd8de 100644
--- a/frontend/components/ToastProvider.tsx
+++ b/frontend/components/ToastProvider.tsx
@@ -99,21 +99,28 @@ export function ToastProvider({ children }: { children: ReactNode }) {
 
   // createPortal needs `document`, which doesn't exist during SSR — mirrors
   // the mounted-guard pattern already used in ThemeToggle.tsx.
-  useEffect(() => setMounted(true), []);
+  useEffect(() => setMounted(true), []);
 
   const dismiss = useCallback((id: string) => {
     setToasts((prev) => prev.filter((t) => t.id !== id));
   }, []);
 
-  const push = useCallback(
+  const push = useCallback(
     (type: ToastType, message: string, duration = DEFAULT_DURATION_MS) => {
       const id = `toast-${nextId.current++}`;
       setToasts((prev) =>
         [...prev, { id, type, message, duration }].slice(-MAX_TOASTS),
       );
     },
-    [],
-  );
+    [],
+  );
+
+  useEffect(() => {
+    const onSessionExpired = () =>
+      push("error", "Your session has expired — please log in again", 0);
+    window.addEventListener("airflex:session-expired", onSessionExpired);
+    return () => window.removeEventListener("airflex:session-expired", onSessionExpired);
+  }, [push]);
 
   const value = useMemo<ToastContextValue>(
     () => ({
@@ -143,4 +150,4 @@ export function ToastProvider({ children }: { children: ReactNode }) {
         )}
     </ToastContext.Provider>
   );
-}
\ No newline at end of file
+}
diff --git a/frontend/lib/apiFetch.test.ts b/frontend/lib/apiFetch.test.ts
index 4e0d34f..05bc00c 100644
--- a/frontend/lib/apiFetch.test.ts
+++ b/frontend/lib/apiFetch.test.ts
@@ -45,4 +45,4 @@ describe("apiFetch authentication", () => {
     const [, options] = mockFetch.mock.calls[0] as [string, RequestInit];
     expect(options.headers).not.toHaveProperty("Authorization");
   });
-});
\ No newline at end of file
+});
diff --git a/frontend/lib/apiFetch.ts b/frontend/lib/apiFetch.ts
index f219bf0..6880e5d 100644
--- a/frontend/lib/apiFetch.ts
+++ b/frontend/lib/apiFetch.ts
@@ -2,7 +2,7 @@
  * apiFetch.ts — Centralized API fetch wrapper and error type for frontend.
  */
 
-import { getToken } from "../app/lib/auth";
+import { clearToken, getToken } from "../app/lib/auth";
 
 export class ApiError extends Error {
   status: number;
@@ -63,6 +63,16 @@ export async function apiFetch<T>(
       // response was not JSON
     }
 
+    if (response.status === 401 && typeof window !== "undefined") {
+      clearToken();
+      window.dispatchEvent(new CustomEvent("airflex:session-expired"));
+
+      const returnTo = `${window.location.pathname}${window.location.search}${window.location.hash}`;
+      if (!window.location.pathname.startsWith("/auth/signup")) {
+        window.location.assign(`/auth/signup?returnTo=${encodeURIComponent(returnTo)}`);
+      }
+    }
+
     throw new ApiError(errorMessage, response.status, errorData);
   }