fix(toc): Track hash in state to fix browser back navigation scrolling

src/components/tableOfContents.tsx

@@ -71,24 +71,53 @@ export function TableOfContents({ignoreIds = []}: Props) {
     setTreeItems(_tocItems);
   }, [ignoreIds]);
 
+  // Track current hash to trigger scroll when it changes (e.g., browser back/forward)
+  const [currentHash, setCurrentHash] = useState('');
+  // Track which hash we've scrolled to for this navigation, to avoid re-scrolling
+  // when treeItems rebuild due to parent re-renders
+  const scrolledHashRef = useRef<string>('');
+
+  useEffect(() => {
+    // Initialize hash and listen for changes
+    setCurrentHash(window.location.hash);
+    const handleHashChange = () => {
+      setCurrentHash(window.location.hash);
+      // Reset scroll tracking on navigation
+      scrolledHashRef.current = '';
+    };
+    window.addEventListener('hashchange', handleHashChange);
+    return () => window.removeEventListener('hashchange', handleHashChange);
+  }, []);
+
   // Re-scroll to hash anchor after TOC renders to compensate for layout shift.
   // The TOC starts empty and populates client-side, which pushes content down
   // and causes the browser's initial anchor scroll to land on the wrong section.
-  const hasScrolledToHash = useRef(false);
+  // This effect runs when:
+  // - treeItems populate initially (layout shift correction)
+  // - Hash changes (navigation, back/forward)
+  // BUT NOT when treeItems rebuild due to parent re-renders (tracked via ref).
+  //
+  // Note: This causes a redundant scroll when clicking TOC links (browser scrolls,
+  // then our effect scrolls again), but the performance impact is negligible and
+  // ensures correct behavior for initial page loads and browser back/forward navigation.
   useEffect(() => {
-    if (hasScrolledToHash.current || treeItems.length === 0) {
-      return;
+    if (treeItems.length === 0 || !currentHash) {
+      return undefined;
     }
-    const hash = window.location.hash;
-    if (!hash) {
-      return;
+    // Skip if we've already scrolled to this hash during this navigation
+    if (scrolledHashRef.current === currentHash) {
+      return undefined;
     }
-    hasScrolledToHash.current = true;
-    requestAnimationFrame(() => {
-      const id = decodeURIComponent(hash.slice(1));
+    const rafId = requestAnimationFrame(() => {
+      // Set the ref inside RAF to ensure we only mark as scrolled when it actually happens
+      scrolledHashRef.current = currentHash;
+      const id = decodeURIComponent(currentHash.slice(1));
       document.getElementById(id)?.scrollIntoView();
     });
-  }, [treeItems]);
+    return () => {
+      cancelAnimationFrame(rafId);
+    };
+  }, [currentHash, treeItems]);
 
   return (
     <ul>