fix: SnapshotStore verweigert nicht kodierbare Snapshots

Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>

tests/Unit/Integrations/Divi/Design/SnapshotStoreTest.php

@@ -87,6 +87,25 @@ final class SnapshotStoreTest extends TestCase
         (new SnapshotStore())->save('presets', ['a' => 1], 'lit/divi-presets-set');
     }
 
+    public function testAnUnencodableSnapshotIsRefusedBeforeAnyWrite(): void
+    {
+        Functions\when('wp_json_encode')->justReturn(false);
+        $written = false;
+        Functions\when('update_option')->alias(function () use (&$written): bool {
+            $written = true;
+
+            return true;
+        });
+
+        try {
+            (new SnapshotStore())->save('presets', ['a' => 1], 'lit/divi-presets-set');
+            self::fail('an unencodable snapshot must be refused');
+        } catch (RuntimeException $e) {
+            self::assertSame('snapshot presets could not be encoded', $e->getMessage());
+        }
+        self::assertFalse($written, 'nothing may be written when the snapshot cannot be encoded');
+    }
+
     public function testCorruptOptionReadsAsEmpty(): void
     {
         $this->options['lit_mcp_snapshots_presets'] = 'kaputt';