toggle giscus as soon as it loads

i did see the iframe query fail once, but was unable to repro
otherwise this seems to be reliable

Author: gordonwoodhull

src/resources/formats/html/giscus/giscus.ejs

@@ -13,5 +13,15 @@
         <%- giscus.loading ? `data-loading=${giscus.loading}` : '' %>
         async>
 </script>
+<script type="application/javascript">
+  window.document.addEventListener("DOMContentLoaded", function (event) {
+    var giscusIframe = window.document.querySelector('iframe.giscus-frame');
+    giscusIframe.addEventListener("load", function() {
+      window.setTimeout(() => {
+        window.toggleGiscusIfUsed(window.hasAlternateSentinel(), authorPrefersDark);
+      }, 100);
+    });
+  });
+</script>
 <input type="hidden" id="giscus-base-theme" value="<%- giscus.baseTheme %>">
 <input type="hidden" id="giscus-alt-theme" value="<%- giscus.altTheme %>">

src/resources/formats/html/templates/quarto-html-before-body.ejs

@@ -188,6 +188,8 @@
       toggleGiscusIfUsed(toAlternate, darkModeDefault);
     };
 
+    window.toggleGiscusIfUsed = toggleGiscusIfUsed;
+
     <% if (respectUserColorScheme) { %>
     queryPrefersDark.addEventListener("change", e => {
       if(window.localStorage.getItem("quarto-color-scheme") !== null)