Fail when the showcase search skips an example a page renders

Plan step 38 review: the index reads example titles out of each
section's source with a regex, which once skipped all six Progress
examples without a sound; the existing test only checked that indexed
anchors exist. A new test renders every section and canonical layout
page and requires the index's examples for it to equal the titled
examples the page draws, both ways, so a format the regex misses (or
an anchor it invents) fails by page.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9

tests/Feature/ShowcaseTest.php

@@ -90,6 +90,33 @@ it('indexes every section, example and component for the search, each linking to
         });
 });
 
+it('indexes exactly the examples each page renders, so an example the index misses fails here', function () {
+    $index = collect($this->getJson('/material/search.json')->assertOk()->json())->where('kind', 'Example');
+    $pages = collect(Sections::all())->keys()->map(fn (string $key): string => route('livewire-material.section', $key, false))
+        ->merge(collect(Sections::layoutPages())->except('layout')->pluck('url'));
+
+    foreach ($pages as $page) {
+        $html = $this->withoutVite()->get($page)->assertOk()->getContent();
+
+        preg_match_all('/<[a-z]+\b[^>]*\bdata-md-showcase-example\b[^>]*>/', $html, $tags);
+
+        $rendered = collect($tags[0])
+            ->map(fn (string $tag): ?string => preg_match('/\bid="([^"]+)"/', $tag, $id) === 1 ? $id[1] : null)
+            ->filter()
+            ->sort()
+            ->values()
+            ->all();
+
+        $indexed = $index->filter(fn (array $entry): bool => strtok($entry['url'], '#') === $page)
+            ->map(fn (array $entry): string => substr($entry['url'], strpos($entry['url'], '#') + 1))
+            ->sort()
+            ->values()
+            ->all();
+
+        expect($indexed)->toBe($rendered, "{$page}: the search index and the page disagree on its examples");
+    }
+});
+
 it('does not mount the showcase when disabled', function () {
     rebootWithShowcase(false);