StructuredContent call tool result, added ability to return error from tool (#93)

src/Schema/Result/CallToolResult.php

@@ -38,12 +38,14 @@ class CallToolResult implements ResultInterface
     /**
      * Create a new CallToolResult.
      *
-     * @param Content[] $content The content of the tool result
-     * @param bool      $isError Whether the tool execution resulted in an error.  If not set, this is assumed to be false (the call was successful).
+     * @param Content[] $content           The content of the tool result
+     * @param bool      $isError           Whether the tool execution resulted in an error.  If not set, this is assumed to be false (the call was successful).
+     * @param mixed[]   $structuredContent JSON content for `structuredContent`
      */
     public function __construct(
         public readonly array $content,
         public readonly bool $isError = false,
+        public readonly ?array $structuredContent = null,
     ) {
         foreach ($this->content as $item) {
             if (!$item instanceof Content) {
@@ -107,9 +109,15 @@ class CallToolResult implements ResultInterface
      */
     public function jsonSerialize(): array
     {
-        return [
+        $result = [
             'content' => $this->content,
             'isError' => $this->isError,
         ];
+
+        if ($this->structuredContent) {
+            $result['structuredContent'] = $this->structuredContent;
+        }
+
+        return $result;
     }
 }

src/Server/Handler/Request/CallToolHandler.php

@@ -59,14 +59,17 @@ final class CallToolHandler implements RequestHandlerInterface
             }
 
             $result = $this->referenceHandler->handle($reference, $arguments);
-            $formatted = $reference->formatResult($result);
+
+            if (!$result instanceof CallToolResult) {
+                $result = new CallToolResult($reference->formatResult($result));
+            }
 
             $this->logger->debug('Tool executed successfully', [
                 'name' => $toolName,
                 'result_type' => \gettype($result),
             ]);
 
-            return new Response($request->getId(), new CallToolResult($formatted));
+            return new Response($request->getId(), $result);
         } catch (ToolNotFoundException $e) {
             $this->logger->error('Tool not found', ['name' => $toolName]);