refine response format

src/Plugins/BotSharp.Plugin.ChartHandler/Functions/PlotChartFn.cs

@@ -48,13 +48,14 @@ public class PlotChartFn : IFunctionCallback
             }
         ]);
 
-        message.Content = "Here is the chart you ask for:";
+        var obj = response.JsonContent<LlmContextOut>();
+        message.Content = obj?.GreetingMessage ?? "Here is the chart you ask for:";
         message.RichContent = new RichContent<IRichMessage>
         {
             Recipient = new Recipient { Id = convService.ConversationId },
             Message = new JsCodeTemplateMessage
             {
-                Text = response
+                Text = obj?.JsCode ?? string.Empty
             }
         };
         message.StopCompletion = true;

src/Plugins/BotSharp.Plugin.ChartHandler/LlmContext/LlmContextOut.cs

@@ -0,0 +1,14 @@
+using System.Text.Json.Serialization;
+
+namespace BotSharp.Plugin.ChartHandler.LlmContext;
+
+public class LlmContextOut
+{
+    [JsonPropertyName("greeting_message")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? GreetingMessage { get; set; }
+
+    [JsonPropertyName("js_code")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? JsCode { get; set; }
+}

src/Plugins/BotSharp.Plugin.ChartHandler/data/agents/6745151e-6d46-4a02-8de4-1c4f21c7da95/templates/util-chart-plot_instruction.liquid

@@ -10,4 +10,11 @@ Please take a look at "Plotting Requirement" and generate a javascript code that
 ** You must output the javascript code only, and wrap it between one pair of script tags.
 ** You need to import Plotly.js in the same script tag. The script source should be "https://cdn.plot.ly/plotly-3.0.1.min.js".
 ** You need to add the MODE bar for each chart you plot.
-** You must not apply any styles on the div html element.
+** You must not apply any styles on the div html element.
+
+*** Response Format ***
+You must output the response in the following JSON format:
+{
+    "greeting_message": "A short polite message that informs user that the charts have been generated.",
+    "js_code": "The javascript code wrapped in a pair of script tags"
+}