fix frontend invoke result handling

frontend/src/a2a.js

@@ -1,6 +1,13 @@
 export const CONFIG_URL = import.meta.env.DEV ? "/config.json" : "./config.json";
 const MAX_CSV_BYTES = 64 * 1024;
 
+export function unwrapInvokeResponse(payload) {
+  if (!payload || typeof payload !== "object") return payload;
+  if ("result" in payload) return payload.result;
+  if ("output" in payload) return payload.output;
+  return payload;
+}
+
 export async function requestJson(url, init = {}) {
   const response = await fetch(url, { credentials: "same-origin", ...init });
   const text = await response.text();
@@ -39,11 +46,12 @@ export function signInUrl(config) {
 
 export async function callSkill(config, skillName, args) {
   try {
-    return await requestJson(`${config.endpoints.invoke}/${encodeURIComponent(skillName)}`, {
+    const payload = await requestJson(`${config.endpoints.invoke}/${encodeURIComponent(skillName)}`, {
       method: "POST",
       headers: { "content-type": "application/json" },
       body: JSON.stringify({ arguments: args }),
     });
+    return unwrapInvokeResponse(payload);
   } catch (err) {
     if (err.status === 401) {
       const target = signInUrl(config);
@@ -55,10 +63,7 @@ export async function callSkill(config, skillName, args) {
 }
 
 export function unwrapA2AResult(response) {
-  if (!response || typeof response !== "object") return response;
-  if ("result" in response) return response.result;
-  if ("output" in response) return response.output;
-  return response;
+  return unwrapInvokeResponse(response);
 }
 
 export async function fileToBrowserUpload(file) {