feat: Basic trip planner agent

agent/utils/format-messages.ts

@@ -0,0 +1,12 @@
+import { BaseMessage } from "@langchain/core/messages";
+
+export function formatMessages(messages: BaseMessage[]): string {
+  return messages
+    .map((m, i) => {
+      const role = m.getType();
+      const contentString =
+        typeof m.content === "string" ? m.content : JSON.stringify(m.content);
+      return `<${role} index="${i}">\n${contentString}\n</${role}>`;
+    })
+    .join("\n");
+}