refine chart plot instruction

Author: Jicheng Lu

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

@@ -1,18 +1,26 @@
 Please take a look at "Plotting Requirement" and generate a javascript code that can be used to render the charts on an html element.
 
-
 === Plotting Requirement ===
 {{ plotting_requirement }}
 
-
-***** Important *****
+***** Hard Requirements *****
 ** Your output must be a single <script>...</script> block with everything needed inside.
 ** You need to import Plotly.js to plot the charts. 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 render the charts on the div html element with id {{ chart_element_id }}.
+** Add a custom mode bar button named "Fullscreen" that toggles the chart container in and out of fullscreen using the Fullscreen API. Requirements for this button:
+    * Always call the Fullscreen API on the chart container div itself (document.getElementById("{{ chart_element_id }}")), not on the document or on Plotly’s SVG.
+    * Use el.requestFullscreen() with fallbacks to el.webkitRequestFullscreen || el.msRequestFullscreen.
+    * Exit fullscreen with document.exitFullscreen() and vendor fallbacks.
+    * Listen for fullscreenchange, webkitfullscreenchange, and msfullscreenchange to keep the button working across repeated clicks and ESC exits.
+    * Ensure the chart fully expands and scales to the entire screen when fullscreen is active.
+    * Provide a simple inline SVG path icon for the button (no external assets).
+    * Use Plotly.newPlot(container, data, layout, {displayModeBar:true, modeBarButtonsToAdd:[fullscreenBtn]});
+    * fullscreenBtn must be a fully-formed object {name, title, icon, click}.
 ** You must not create any new html element.
 ** You must not apply any styles on any html element.
-** You must generate as less token as possible.
+** Keep code compact (few tokens), but fix all errors before returning.
+** Please fix any code errors before returning the final response.
 
 *** Response Format ***
 You must output the response in the following JSON format: