fix: iframe页面子智能体不跳出，增加按钮

frontend-web/src/pages/iframe-chat-agent.ts

@@ -0,0 +1,19 @@
+type ResolveIframeAssistantIdInput = {
+  selectedAgentId: string | null;
+  threadMetadataAgentId: string | null;
+};
+
+function normalizeAgentId(agentId: string | null | undefined): string | undefined {
+  const trimmed = agentId?.trim();
+  return trimmed ? trimmed : undefined;
+}
+
+export function resolveIframeAssistantId({
+  selectedAgentId,
+  threadMetadataAgentId,
+}: ResolveIframeAssistantIdInput): string | undefined {
+  return (
+    normalizeAgentId(selectedAgentId) ??
+    normalizeAgentId(threadMetadataAgentId)
+  );
+}