chore(website): final-review polish for the library pages arc

- section-media.ts libRender: SolutionCode's language union is typescript |
  python | html — no 'json' — so the code block stays tagged typescript
  (noted inline); simplified its dead label to 'spec.json'.
- section-media.ts: the library-entries comment described Task 3's
  not-yet-done deletion of the page-local mocks; rewritten to present tense
  now that the pages consume these entries and the mocks are gone. Also
  documented the /ag-ui deviation (switcher lands on its second block,
  BackendsGrid stays on the first) directly on libAgUi.
- FinalCTA.spec.tsx: test name said "8 non-home pages" — now 4 after the
  library pages moved to the dark closer.
- library-pages-design.md §1: amended the FIRST FeatureBlock sentence with
  the ratified /ag-ui deviation.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: blove

apps/website/src/components/landing/FinalCTA.spec.tsx

@@ -11,7 +11,7 @@ vi.mock('../../lib/analytics/client', () => ({
 }));
 
 describe('FinalCTA', () => {
-  it('defaults to the tinted surface (used by 8 non-home pages)', () => {
+  it('defaults to the tinted surface (used by 4 non-home pages)', () => {
     const { container } = render(<FinalCTA />);
     expect(
       container.querySelector('[data-ui="section"]')?.getAttribute('data-surface'),

apps/website/src/lib/section-media.ts

@@ -113,10 +113,10 @@ const catalog = views({
   },
 
   // The four library pages (/langgraph, /chat, /ag-ui, /render) reuse this
-  // table for their first FeatureBlock's medium switcher. Code sources below
-  // are lifted verbatim from each page's current static mock content — Task
-  // 3 of the library-pages plan deletes those page-local copies once the
-  // switcher is wired in, so for now the same source lives in both places.
+  // table for their first FeatureBlock's medium switcher — except /ag-ui,
+  // whose switcher replaces its SECOND block's mock (see libAgUi below). The
+  // pages consume these entries via buildPanes; the page-local static mocks
+  // they were lifted from are gone.
   libLanggraph: {
     video: LANGGRAPH_CLIP,
     live: { featured: 'tell-me-about-coral' },
@@ -153,7 +153,9 @@ export class ChatComponent {
   libAgUi: {
     video: AG_UI_CLIP,
     // No live tab: the demo host speaks LangGraph, and wiring AG-UI into it
-    // live is out of scope for this arc.
+    // live is out of scope for this arc. Unlike the other three pages, this
+    // switcher lands on /ag-ui's SECOND FeatureBlock — its first block's
+    // visual is the real BackendsGrid, not a mock.
     code: [
       {
         label: 'app.config.ts',
@@ -186,7 +188,9 @@ export class App {
     live: { featured: 'generative-ui-contact-form' },
     code: [
       {
-        label: 'render · spec → component',
+        // 'json' isn't in SolutionCode's language union (typescript | python
+        // | html), so this stays tagged typescript for Shiki highlighting.
+        label: 'spec.json',
         language: 'typescript',
         source: `{
   "type": "card",

docs/superpowers/specs/2026-08-31-library-pages-design.md

@@ -15,7 +15,9 @@ the homepage wall).
 Each page's FIRST FeatureBlock swaps its static BrowserFrame mock for
 `MediumSwitcher`, panes built server-side via the homepage's `buildPanes`
 pattern (extract that helper from `app/page.tsx` into a shared module rather
-than copy it — it is currently page-local). The SECOND FeatureBlock keeps its
+than copy it — it is currently page-local). (/ag-ui deviates: its first
+block's visual is the real BackendsGrid; the switcher replaces the static
+mock on its second block instead.) The SECOND FeatureBlock keeps its
 CodeShowcase untouched.
 
 New `SECTION_MEDIA` entries (validation via the existing section-media.spec