feat: harden runtime readiness and session workflow

frontend/src/api/client.ts

@@ -12,7 +12,11 @@ export async function apiFetch<T>(path: string, init?: RequestInit): Promise<T>
   }
   const res = await fetch(joinBackendPath(BASE, path), { ...init, headers });
   if (!res.ok) throw new Error(`${res.status} ${await res.text().catch(() => "")}`);
-  return res.status === 204 ? (undefined as T) : ((await res.json()) as T);
+  if (res.status === 204) return undefined as T;
+  // Accepted fire-and-forget endpoints may legitimately return 202 with no
+  // representation. Keep apiFetch useful for both 202 and 204 contracts.
+  const body = await res.text();
+  return body ? (JSON.parse(body) as T) : (undefined as T);
 }
 
 export { BASE };