Added basic StructuredContent

Author: ineersa

src/Schema/Result/CallToolResult.php

@@ -98,6 +98,8 @@ public static function fromArray(array $data): self
                 continue;
             }
             $contents[] = match ($item->type ?? null) {
+                // TODO this should be enum, also `resource_link` missing.
+                // We shouldn't rely on user input for type and just use instanceof instead
                 'text', 'audio', 'image', 'resource' => $item,
                 default => throw new InvalidArgumentException(\sprintf('Invalid content type in CallToolResult data: "%s".', $item['type'] ?? null)),
             };
@@ -124,9 +126,7 @@ public function jsonSerialize(): array
             $result['content'][] = $item->jsonSerialize();
         }
 
-        $result = [
-            'isError' => $this->isError,
-        ];
+        $result['isError'] = $this->isError;
 
         if ($this->structuredContent) {
             $result['structuredContent'] = $this->structuredContent->jsonSerialize();