diff --git a/frontend/src/a2a.js b/frontend/src/a2a.js
index 498212a..ba52308 100644
--- a/frontend/src/a2a.js
+++ b/frontend/src/a2a.js
@@ -6,7 +6,9 @@ export async function requestJson(url, init = {}) {
   const data = text ? JSON.parse(text) : null;
   if (!response.ok) {
     const detail = data && (data.detail || data.message);
-    throw new Error(detail || `request failed: ${response.status}`);
+    const err = new Error(detail || `request failed: ${response.status}`);
+    err.status = response.status;
+    throw err;
   }
   return data;
 }
@@ -20,10 +22,6 @@ export async function loadSession(config) {
 }
 
 export function signInUrl(config) {
-  // Always prefer authorizeUrl. The dashboard's login cookie is host-locked to
-  // the dashboard's own origin, so sending the browser straight to loginUrl
-  // signs the user in *there* and bounces back here still signed out.
-  // authorizeUrl hands this origin a code it trades for its own session.
   const target = config.auth?.authorizeUrl || config.auth?.loginUrl;
   if (!target) return null;
   const next = encodeURIComponent(
@@ -43,43 +41,28 @@ export async function requireSession(config) {
 }
 
 export async function callSkill(config, skillName, args) {
-  if (config.auth?.invokeRequiresSession) {
-    await requireSession(config);
-  }
-  return requestJson(
-    `${config.endpoints.invoke}/${encodeURIComponent(skillName)}`,
-    {
-      method: "POST",
-      headers: { "content-type": "application/json" },
-      body: JSON.stringify({ arguments: args }),
-    },
-  );
-}
-
-export function sampleValue(schema) {
-  if (!schema || typeof schema !== "object") return null;
-  if ("default" in schema) return schema.default;
-  if ("const" in schema) return schema.const;
-  if (Array.isArray(schema.enum) && schema.enum.length) return schema.enum[0];
-  const type = Array.isArray(schema.type)
-    ? schema.type.find((item) => item !== "null") || schema.type[0]
-    : schema.type;
-  if (type === "array") return [];
-  if (type === "boolean") return false;
-  if (type === "integer" || type === "number") return 0;
-  if (type === "string") return "";
-  const props = schema.properties || {};
-  if (type === "object" || Object.keys(props).length) {
-    const required = Array.isArray(schema.required) ? schema.required : Object.keys(props);
-    return Object.fromEntries(
-      required.map((key) => [key, sampleValue(props[key])]),
+  try {
+    if (config.auth?.invokeRequiresSession) {
+      await requireSession(config);
+    }
+    const data = await requestJson(
+      `${config.endpoints.invoke}/${encodeURIComponent(skillName)}`,
+      {
+        method: "POST",
+        headers: { "content-type": "application/json" },
+        body: JSON.stringify({ arguments: args }),
+      },
     );
+    if (data?.status === "setup_required") {
+      throw new Error(data.message || "Setup required before running this workflow.");
+    }
+    return data;
+  } catch (err) {
+    if (err?.status === 401) {
+      const target = signInUrl(config);
+      if (target) window.location.assign(target);
+      throw new Error("Session expired. Sign in again to run ContractClock.");
+    }
+    throw err;
   }
-  return null;
-}
-
-export function sampleArgs(skill) {
-  const schema = skill?.input_schema || skill?.inputSchema || {};
-  const value = sampleValue(schema);
-  return value && typeof value === "object" && !Array.isArray(value) ? value : {};
 }