Docs: Fixed some bugs int he ToC's javascript

docs/javascripts/toc-collapse.js

@@ -74,15 +74,19 @@
     userPinned.clear();
     autoExpanded.clear();
 
-    // Mark all nav roots so CSS can scope styles
-    sidebar.querySelectorAll("nav.md-nav").forEach(function (nav) {
-      nav.classList.add("md-nav--integrated");
-    });
-
-    // Find every <li> inside the actual TOC (md-nav--secondary) that has
-    // nested children.  We scope to the secondary nav to avoid touching the
-    // page-level nav item that wraps the TOC — that item contains a <label>
-    // for the mobile TOC toggle and would show up as a bogus duplicate entry.
+    // Find the actual TOC (md-nav--secondary).  We scope to the secondary
+    // nav to avoid touching the page-level nav items that wrap sections —
+    // those use Material's native checkbox-based toggle and should not be
+    // overridden.
+    //
+    // NOTE: The primary nav already has .md-nav--integrated added by
+    // mkdocs-material when the toc.integrate feature is enabled.  We do
+    // NOT re-add that class or extend it to descendant navs — doing so
+    // causes the CSS rule ".md-nav--integrated .md-nav__item--nested >
+    // .md-nav { display: block }" to override Material's native
+    // checkbox-based collapse on primary nav sections (Reference,
+    // Development, Architecture Decisions, etc.), creating whitespace
+    // below collapsed section headings.
     var tocNav = sidebar.querySelector("nav.md-nav--secondary");
     if (!tocNav) return;