fix(posts): cache the link card as an array, not the DTO

The link-card cache stored a LinkCardMetadata object, which does not round-trip through the Redis cache driver — a cache hit came back as __PHP_Incomplete_Class and 500'd the preview endpoint. Cache the plain array (toArray) and rebuild the DTO via a new fromArray(). Primitives round-trip cleanly through every driver. The cache test now asserts a primitive is stored and a hit reconstructs the DTO; the array cache driver used in tests hid the bug because it never serializes.

app/Services/Social/LinkCard/LinkCardFetcher.php

@@ -32,11 +32,16 @@ public function fetch(string $text): ?LinkCardMetadata
             return null;
         }
 
-        return Cache::remember(
+        // Cache a plain array, never the DTO: a rich object does not round-trip
+        // cleanly through every cache driver (it comes back as an incomplete
+        // class), whereas primitives always do.
+        $data = Cache::remember(
             'link_card:'.sha1($url),
             now()->addMinutes(self::CACHE_MINUTES),
-            fn (): ?LinkCardMetadata => $this->build($url),
+            fn (): ?array => $this->build($url)?->toArray(),
         );
+
+        return $data === null ? null : LinkCardMetadata::fromArray($data);
     }
 
     private function build(string $url): ?LinkCardMetadata

app/Services/Social/LinkCard/LinkCardMetadata.php

@@ -16,6 +16,22 @@ public function __construct(
         public ?string $imageUrl,
     ) {}
 
+    /**
+     * Rebuild the DTO from its cached array form (the inverse of toArray, minus
+     * the derived `domain`, which toArray recomputes).
+     *
+     * @param  array{uri?: string, title?: string, description?: string, image?: ?string}  $data
+     */
+    public static function fromArray(array $data): self
+    {
+        return new self(
+            uri: (string) data_get($data, 'uri', ''),
+            title: (string) data_get($data, 'title', ''),
+            description: (string) data_get($data, 'description', ''),
+            imageUrl: data_get($data, 'image'),
+        );
+    }
+
     /**
      * @return array{uri: string, domain: string, title: string, description: string, image: ?string}
      */

tests/Feature/Services/Social/LinkCard/LinkCardFetcherTest.php

@@ -3,6 +3,8 @@
 declare(strict_types=1);
 
 use App\Services\Social\LinkCard\LinkCardFetcher;
+use App\Services\Social\LinkCard\LinkCardMetadata;
+use Illuminate\Support\Facades\Cache;
 use Illuminate\Support\Facades\Http;
 
 // example.com resolves to a public IP so the SafeHttpFetcher SSRF guard passes;
@@ -50,8 +52,16 @@
     ]);
 
     $fetcher = app(LinkCardFetcher::class);
-    $fetcher->fetch('https://example.com');
-    $fetcher->fetch('https://example.com');
+    $first = $fetcher->fetch('https://example.com');
+    $second = $fetcher->fetch('https://example.com');
 
     Http::assertSentCount(1);
+
+    // The cache must hold a primitive array, not the DTO — a rich object does
+    // not round-trip through every cache driver (it comes back as an incomplete
+    // class). A cache hit still reconstructs a proper DTO.
+    expect(Cache::get('link_card:'.sha1('https://example.com')))->toBeArray();
+    expect($second)->toBeInstanceOf(LinkCardMetadata::class)
+        ->and($second->uri)->toBe($first->uri)
+        ->and($second->title)->toBe('Cached');
 });