fix: no attachment broadcast fix

lib/broadcasts.ts

@@ -18,8 +18,14 @@ async function call<T>(path: string, init?: RequestInit): Promise<T> {
   });
   if (!res.ok) throw new Error(`broadcast request failed: ${res.status}`);
   if (res.status === 204) return undefined as T;
-  const json = await res.json();
-  return (json?.data ?? json) as T;
+  const body = (await res.json().catch(() => ({}))) as {
+    data?: T;
+    success?: boolean;
+  };
+  // NOT `body.data ?? body`: /pending answers {data: null} when nothing is
+  // waiting, and `??` would fall through and hand back the whole envelope —
+  // which is truthy, so the modal would try to render it as an announcement.
+  return (body.data ?? (null as unknown as T)) as T;
 }
 
 export type Broadcast = {