the open page lists its bands in the nav

A third level, under the selected page only — every page has bands, and listing
all of them would make the nav longer than the site.

Announced by the builder rather than fetched again: it already reads them to know
what it is looking at in the document, and it mounts exactly when a page is open.
Cleared on unmount, or the nav keeps listing the last page's bands.

Clicking one writes a third URL segment and the preview scrolls to it, keyed on
the render count too so the position survives a save replacing the frame.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

web/NavPanel.tsx

@@ -5,7 +5,7 @@ import { GripVertical, Lock } from 'lucide-react';
 import { SECTIONS, sectionOpen } from './sections';
 import { href, useNav } from './routes';
 import { useReady } from './useReady';
-import { pageParam, usePages, type Page } from './usePages';
+import { pageParam, usePages, useSections, type Page } from './usePages';
 import { useFofosChanged } from './channel';
 
 /**
@@ -54,7 +54,8 @@ const rowClass = (active: boolean) =>
 
 export const NavPanel = () => {
   const { pages, announce } = usePages();
-  const { section: active, item } = useNav();
+  const { section: active, item, part } = useNav();
+  const { sections } = useSections();
   const { ready, rootSet } = useReady();
 
   /*
@@ -202,8 +203,8 @@ export const NavPanel = () => {
           const current = active === 'pages' && item === pageParam(page);
 
           return (
-            <div
-              key={page.id}
+            <div key={page.id} className="flex flex-col">
+              <div
               /*
                 The ROW is the drop target and the HANDLE is what drags.
 
@@ -253,6 +254,28 @@ export const NavPanel = () => {
                     tells them apart. Home's is `/`, which is short enough not to need explaining. */}
                 <span className="shrink-0 font-mono text-[10px] text-muted-foreground">{page.path}</span>
               </Link>
+              </div>
+
+              {/*
+                The open page's bands, one level further in.
+
+                Only under the page that is SELECTED — every page has bands, and listing all of them
+                would make the nav longer than the site. Announced by the builder, which is mounted
+                exactly when a page is open; see useSections.
+              */}
+              {current &&
+                sections?.map((band) => (
+                  <Link
+                    key={band.id}
+                    to={href('pages', pageParam(page), String(band.id))}
+                    replace
+                    className={`flex items-baseline border-b border-border py-1.5 pr-3 pl-14 text-left transition-colors ${
+                      part === String(band.id) ? 'bg-muted' : 'hover:bg-muted/50'
+                    }`}
+                  >
+                    <span className="min-w-0 flex-1 truncate text-xs text-muted-foreground">{band.name}</span>
+                  </Link>
+                ))}
             </div>
           );
         })}

web/routes.ts

@@ -32,14 +32,16 @@ export const MOUNT = '/fofos-admin';
  * redirects, so the address bar ends up saying where you are. `section` is still defaulted, so
  * everything that only wants to draw a highlight has one answer rather than a branch.
  */
-export const useNav = (): { section: SectionKey; item: string | null; atIndex: boolean } => {
+export const useNav = (): { section: SectionKey; item: string | null; part: string | null; atIndex: boolean } => {
   const { pathname } = useLocation();
   const rest = pathname.startsWith(MOUNT) ? pathname.slice(MOUNT.length) : '';
-  const [first = '', second = ''] = rest.replace(/^\//, '').split('/');
+  const [first = '', second = '', third = ''] = rest.replace(/^\//, '').split('/');
   return {
     // An unknown segment falls back rather than 404s: the URL is a thing people type and edit.
     section: isSectionKey(first) ? first : DEFAULT_SECTION,
     item: second ? decodeURIComponent(second) : null,
+    /** Something inside the item — a band of the open page. Nothing else uses a third segment yet. */
+    part: third ? decodeURIComponent(third) : null,
     atIndex: first === '',
   };
 };
@@ -51,5 +53,8 @@ export const useNav = (): { section: SectionKey; item: string | null; atIndex: b
  * you are looking at the Layout preview; carrying it into Galleries would be state from one screen
  * deciding something on another. A panel that wants a parameter to survive says so at its own link.
  */
-export const href = (section: SectionKey, item?: string | null): string =>
-  item ? `${MOUNT}/${section}/${encodeURIComponent(item)}` : `${MOUNT}/${section}`;
+export const href = (section: SectionKey, item?: string | null, part?: string | null): string => {
+  if (!item) return `${MOUNT}/${section}`;
+  const base = `${MOUNT}/${section}/${encodeURIComponent(item)}`;
+  return part ? `${base}/${encodeURIComponent(part)}` : base;
+};

web/sections/PageBuilderPanel.tsx

@@ -35,7 +35,7 @@ import { useEditorSlot } from '../useEditorSlot';
 import { AddComponentDialog, type ComponentKind } from './AddComponentDialog';
 import { MediaPicker } from '../MediaPicker';
 import { GalleryPicker } from '../GalleryPicker';
-import { pageFromParam, usePages, type Page } from '../usePages';
+import { pageFromParam, usePages, useSections, type Page } from '../usePages';
 
 /**
  * One page, being built.
@@ -57,10 +57,14 @@ export const PageBuilderPanel = () => {
   const clientRef = useRef(client);
   clientRef.current = client;
 
-  const { item: slug } = useNav();
+  const { item: slug, part } = useNav();
 
   const devPort = useDevPort();
   const { pages, announce } = usePages();
+  const { announceSections } = useSections();
+  // Cleared when this unmounts, or the nav goes on listing the last page's bands under whatever is
+  // selected next.
+  useEffect(() => () => announceSections(null), [announceSections]);
 
   // This section has a preview, so the bar offers Edit/View and the three widths — the same opt-in
   // Layout makes. Pages, the list, does not: there is nothing there to view at tablet width.
@@ -160,6 +164,21 @@ export const PageBuilderPanel = () => {
   */
   const frameDoc = useRef<Document | null>(null);
 
+  /*
+    The band named by the third URL segment, brought into view.
+
+    That segment is what the nav's rows under the open page write, and this is what makes them do
+    something. `rendered` is a dependency as well as `part`: the frame is replaced on every write, and
+    a scroll issued against the old document would be lost — this way the position survives a save.
+
+    The band is found by `data-section-id`, the marker the site already carries for the admin.
+  */
+  useEffect(() => {
+    if (!part) return;
+    const band = frameDoc.current?.querySelector(`[data-section-id="${CSS.escape(part)}"]`);
+    band?.scrollIntoView({ behavior: 'smooth', block: 'start' });
+  }, [part, rendered]);
+
   const onDocument = useCallback(
     (frameDocument: Document) => {
       frameDoc.current = frameDocument;
@@ -246,6 +265,9 @@ export const PageBuilderPanel = () => {
       .get<{ data: CanvasSection[]; steps?: number[] }>(`/fofos-admin/pages/${page.id}/sections`)
       .then((response) => {
         setSections(response.data);
+        // The nav draws these as rows under the open page — see useSections for why it is announced
+        // rather than fetched a second time.
+        announceSections(response.data.map((section) => ({ id: section.id, name: section.name })));
         if (response.steps) setSteps(response.steps);
       })
       .catch((failure: unknown) => setError(readableError(failure)));

web/usePages.ts

@@ -60,3 +60,32 @@ export const pageFromParam = (pages: Page[] | null, value: string | null): Page
   if (!pages || !value) return null;
   return pages.find((page) => pageParam(page) === value) ?? null;
 };
+
+/**
+ * The selected page's sections, shared between the builder and the nav.
+ *
+ * ── Announced, not fetched twice ──
+ *
+ * The page builder already reads them — it needs their names and columns to know what it is looking at
+ * in the rendered document — and the nav draws them as rows under the open page. Two fetchers would
+ * agree until somebody renamed a band.
+ *
+ * The builder mounts whenever a page is selected, and the nav only draws these under the page that is
+ * selected, so there is no state where the nav wants them and nothing has spoken.
+ *
+ * Null means nobody has said yet: the nav then draws no rows rather than an empty list, which would
+ * read as "this page has no sections".
+ */
+export type NamedSection = { id: number; name: string };
+
+const useSectionsList = defineChannel<NamedSection[] | null>('fofos-admin:sections', null);
+
+export const useSections = () => {
+  const [sections, setSections] = useSectionsList();
+
+  const setRef = useRef(setSections);
+  setRef.current = setSections;
+  const announceSections = useCallback((rows: NamedSection[] | null) => setRef.current(rows), []);
+
+  return { sections, announceSections };
+};