also handle non-connected notebook mode we use in dashboard

In this case, plotly.py will embed the full plotly.js library so we need to dectect this code cell and put it in the html head to not have a non figure div in the output

Author: cderv

src/core/jupyter/widgets.ts

@@ -190,11 +190,29 @@ function isWidgetIncludeHtml(html: string) {
 }
 
 function isPlotlyLibrary(html: string) {
-  return (/^\s*<script type="text\/javascript">/.test(html) &&
+  // Plotly before version 6 used require.js to load the library
+  const hasRequireScript = (
+    html: string,
+  ) => (/^\s*<script type="text\/javascript">/.test(html) &&
     (/require\.undef\(["']plotly["']\)/.test(html) ||
-      /define\('plotly'/.test(html))) ||
-    // also handle new module syntax from plotly.py 6+
+      /define\('plotly'/.test(html)));
+  // Plotly 6+ uses the new module syntax
+  const hasModuleScript = (html: string) =>
     /\s*<script type=\"module\">import .*plotly.*<\/script>/.test(html);
+  // notebook mode non connected embed plotly.js scripts like this:
+  //  * plotly.js v3.0.1
+  //  * Copyright 2012-2025, Plotly, Inc.
+  //  * All rights reserved.
+  //  * Licensed under the MIT license
+  const hasEmbedScript = (
+    html: string,
+  ) => (/\* plotly\.js v\d+\.\d+\.\d+\s*\n\s*\* Copyright \d{4}-\d{4}, Plotly, Inc\.\s*\n\s*\* All rights reserved\.\s*\n\s*\* Licensed under the MIT license/
+    .test(html));
+  return hasRequireScript(html) ||
+    // also handle new module syntax from plotly.py 6+
+    hasModuleScript(html) ||
+    // detect plotly by its copyright header
+    hasEmbedScript(html);
 }
 
 function htmlLibrariesText(htmlText: string) {

tests/docs/smoke-all/jupyter/subfigures/plotly.qmd

@@ -1,7 +1,5 @@
 ---
 title: "Bugged plotly figure: phantom subfigure"
-keep-ipynb: true
-keep-md: true
 _quarto:
   tests: 
     html:
@@ -17,6 +15,19 @@ _quarto:
       ensureHtmlElementCount:
         selectors: ['figure.quarto-float-fig figure.quarto-subfloat-fig']
         counts: [2]
+    dashboard:
+      ensureHtmlElements:
+        - 
+          - 'figure.quarto-float-fig div#fig-gapminder-1 figure.quarto-subfloat-fig div.plotly-graph-div'
+          - 'figure.quarto-float-fig div#fig-gapminder-2 figure.quarto-subfloat-fig div.plotly-graph-div'
+      ensureHtmlElementContents:
+        selectors: 
+          - 'div#fig-gapminder-1 figcaption.quarto-subfloat-caption'
+          - 'div#fig-gapminder-2 figcaption.quarto-subfloat-caption'
+        matches: ['\((a|b)\) Gapminder: (1957|2007)']
+      ensureHtmlElementCount:
+        selectors: ['figure.quarto-float-fig figure.quarto-subfloat-fig']
+        counts: [2]
 ---
 
 ```{python}