M54: harden operations and demo resilience

frontend/src/context/DemoManifestContext.tsx

@@ -5,6 +5,7 @@ import type { DemoManifest } from "../api/types";
 interface DemoManifestState {
   manifest: DemoManifest | null;
   loading: boolean;
+  error: boolean;
   refresh: () => void;
 }
 
@@ -13,32 +14,34 @@ const DemoManifestContext = createContext<DemoManifestState | undefined>(undefin
 export function DemoManifestProvider({ children }: { children: ReactNode }) {
   const [manifest, setManifest] = useState<DemoManifest | null>(null);
   const [loading, setLoading] = useState(true);
+  const [error, setError] = useState(false);
   const [version, setVersion] = useState(0);
 
   useEffect(() => {
-    let cancelled = false;
+    const controller = new AbortController();
     setLoading(true);
+    setError(false);
     // Public endpoint by design: the demo-entry screen needs this before any session
     // exists, so it is never gated behind auth.
     api
-      .get<DemoManifest>("/api/v1/demo/manifest")
+      .get<DemoManifest>("/api/v1/demo/manifest", { signal: controller.signal })
       .then((result) => {
-        if (!cancelled) setManifest(result);
+        if (!controller.signal.aborted) setManifest(result);
       })
       .catch(() => {
-        if (!cancelled) setManifest(null);
+        if (controller.signal.aborted) return;
+        setManifest(null);
+        setError(true);
       })
       .finally(() => {
-        if (!cancelled) setLoading(false);
+        if (!controller.signal.aborted) setLoading(false);
       });
-    return () => {
-      cancelled = true;
-    };
+    return () => controller.abort();
   }, [version]);
 
   return (
     <DemoManifestContext.Provider
-      value={{ manifest, loading, refresh: () => setVersion((v) => v + 1) }}
+      value={{ manifest, loading, error, refresh: () => setVersion((v) => v + 1) }}
     >
       {children}
     </DemoManifestContext.Provider>