feat: add system message for flowchart assistance and improve message handling in chat API

app/api/chat/route.ts

@@ -15,7 +15,24 @@ interface ToolContext {
 }
 
 export async function POST(req: Request) {
-  const { messages } = await req.json();
+  let { messages } = await req.json();
+  const systemMessage = `
+  You are a helpful assistant that can create, edit, and display flowcharts using draw.io.
+  You can use the following tools:
+  - display_flow_chart: Display a flowchart on draw.io.
+  - fetch_flow_chart: Get the current flowchart XML from draw.io.
+  You can use the tools to create and manipulate flowcharts.
+  You can also answer questions and provide explanations.
+  `;
+  if (messages.length === 1) {
+    messages = [
+      {
+        "role": "system",
+        "content": systemMessage,
+      },
+      ...messages,
+    ];
+  }
   const response = streamText({
     model: google("gemini-2.0-flash"),
     messages,