Introduce schema component

src/Schema/ResourceReference.php

@@ -0,0 +1,44 @@
+<?php
+
+/*
+ * This file is part of the official PHP MCP SDK.
+ *
+ * A collaboration between Symfony and the PHP Foundation.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Mcp\Schema;
+
+/**
+ * A reference to a resource or resource template definition.
+ *
+ * @author Kyrian Obikwelu <koshnawaza@gmail.com>
+ */
+class ResourceReference implements \JsonSerializable
+{
+    public string $type = 'ref/resource';
+
+    /**
+     * @param string $uri the URI or URI template of the resource
+     */
+    public function __construct(
+        public readonly string $uri,
+    ) {
+    }
+
+    /**
+     * @return array{
+     *     type: string,
+     *     uri: string,
+     * }
+     */
+    public function jsonSerialize(): array
+    {
+        return [
+            'type' => $this->type,
+            'uri' => $this->uri,
+        ];
+    }
+}