Roll out meta properties in attributes and more schema classes (#129)

src/Schema/Prompt.php

@@ -22,6 +22,7 @@ use Mcp\Exception\InvalidArgumentException;
  *     name: string,
  *     description?: string,
  *     arguments?: PromptArgumentData[],
+ *     _meta?: array<string, mixed>
  * }
  *
  * @author Kyrian Obikwelu <koshnawaza@gmail.com>
@@ -32,11 +33,13 @@ class Prompt implements \JsonSerializable
      * @param string                $name        the name of the prompt or prompt template
      * @param string|null           $description an optional description of what this prompt provides
      * @param PromptArgument[]|null $arguments   A list of arguments for templating. Null if not a template.
+     * @param ?array<string, mixed> $meta        Optional metadata
      */
     public function __construct(
         public readonly string $name,
         public readonly ?string $description = null,
         public readonly ?array $arguments = null,
+        public readonly ?array $meta = null,
     ) {
         if (null !== $this->arguments) {
             foreach ($this->arguments as $arg) {
@@ -60,10 +63,15 @@ class Prompt implements \JsonSerializable
             $arguments = array_map(fn (array $argData) => PromptArgument::fromArray($argData), $data['arguments']);
         }
 
+        if (!empty($data['_meta']) && !\is_array($data['_meta'])) {
+            throw new InvalidArgumentException('Invalid "_meta" in Prompt data.');
+        }
+
         return new self(
             name: $data['name'],
             description: $data['description'] ?? null,
-            arguments: $arguments
+            arguments: $arguments,
+            meta: isset($data['_meta']) ? $data['_meta'] : null
         );
     }
 
@@ -71,7 +79,8 @@ class Prompt implements \JsonSerializable
      * @return array{
      *     name: string,
      *     description?: string,
-     *     arguments?: array<PromptArgument>
+     *     arguments?: array<PromptArgument>,
+     *     _meta?: array<string, mixed>
      * }
      */
     public function jsonSerialize(): array
@@ -83,6 +92,9 @@ class Prompt implements \JsonSerializable
         if (null !== $this->arguments) {
             $data['arguments'] = $this->arguments;
         }
+        if (null !== $this->meta) {
+            $data['_meta'] = $this->meta;
+        }
 
         return $data;
     }