Add title field to Prompt for MCP spec compliance (#278)

The MCP 2025-11-25 specification defines an optional `title` property on
Prompt for human-readable display in UI contexts, distinct from the
programmatic `name` identifier. This was missing from the SDK.

BC Break: Builder::addPrompt() signature changed — $title parameter added
between $name and $description. Callers using positional arguments for
$description must switch to named arguments.

Closes #276

src/Capability/Attribute/McpPrompt.php

@@ -24,12 +24,14 @@ class McpPrompt
 {
     /**
      * @param ?string               $name        overrides the prompt name (defaults to method name)
+     * @param ?string               $title       Optional human-readable title for display in UI
      * @param ?string               $description Optional description of the prompt. Defaults to method DocBlock summary.
      * @param ?Icon[]               $icons       Optional list of icon URLs representing the prompt
      * @param ?array<string, mixed> $meta        Optional metadata
      */
     public function __construct(
         public ?string $name = null,
+        public ?string $title = null,
         public ?string $description = null,
         public ?array $icons = null,
         public ?array $meta = null,

src/Capability/Discovery/Discoverer.php

@@ -276,7 +276,7 @@ final class Discoverer implements DiscovererInterface
                         $paramTag = $paramTags['$'.$param->getName()] ?? null;
                         $arguments[] = new PromptArgument($param->getName(), $paramTag ? trim((string) $paramTag->getDescription()) : null, !$param->isOptional() && !$param->isDefaultValueAvailable());
                     }
-                    $prompt = new Prompt($name, $description, $arguments, $instance->icons, $instance->meta);
+                    $prompt = new Prompt($name, $instance->title, $description, $arguments, $instance->icons, $instance->meta);
                     $completionProviders = $this->getCompletionProviders($method);
                     $prompts[$name] = new PromptReference($prompt, [$className, $methodName], false, $completionProviders);
                     ++$discoveredCount['prompts'];

src/Capability/Registry/Loader/ArrayLoader.php

@@ -252,6 +252,7 @@ final class ArrayLoader implements LoaderInterface
                 }
                 $prompt = new Prompt(
                     name: $name,
+                    title: $data['title'] ?? null,
                     description: $description,
                     arguments: $arguments,
                     icons: $data['icons'] ?? null,

src/Schema/Prompt.php

@@ -21,6 +21,7 @@ use Mcp\Exception\InvalidArgumentException;
  *
  * @phpstan-type PromptData array{
  *     name: string,
+ *     title?: string,
  *     description?: string,
  *     arguments?: PromptArgumentData[],
  *     icons?: IconData[],
@@ -33,6 +34,7 @@ class Prompt implements \JsonSerializable
 {
     /**
      * @param string                $name        the name of the prompt or prompt template
+     * @param ?string               $title       Optional human-readable title for display in UI
      * @param ?string               $description an optional description of what this prompt provides
      * @param ?PromptArgument[]     $arguments   A list of arguments for templating. Null if not a template.
      * @param ?Icon[]               $icons       optional icons representing the prompt
@@ -40,6 +42,7 @@ class Prompt implements \JsonSerializable
      */
     public function __construct(
         public readonly string $name,
+        public readonly ?string $title = null,
         public readonly ?string $description = null,
         public readonly ?array $arguments = null,
         public readonly ?array $icons = null,
@@ -73,6 +76,7 @@ class Prompt implements \JsonSerializable
 
         return new self(
             name: $data['name'],
+            title: $data['title'] ?? null,
             description: $data['description'] ?? null,
             arguments: $arguments,
             icons: isset($data['icons']) && \is_array($data['icons']) ? array_map(Icon::fromArray(...), $data['icons']) : null,
@@ -83,6 +87,7 @@ class Prompt implements \JsonSerializable
     /**
      * @return array{
      *     name: string,
+     *     title?: string,
      *     description?: string,
      *     arguments?: array<PromptArgument>,
      *     icons?: Icon[],
@@ -92,6 +97,9 @@ class Prompt implements \JsonSerializable
     public function jsonSerialize(): array
     {
         $data = ['name' => $this->name];
+        if (null !== $this->title) {
+            $data['title'] = $this->title;
+        }
         if (null !== $this->description) {
             $data['description'] = $this->description;
         }

src/Server/Builder.php

@@ -473,11 +473,12 @@ final class Builder
     public function addPrompt(
         \Closure|array|string $handler,
         ?string $name = null,
+        ?string $title = null,
         ?string $description = null,
         ?array $icons = null,
         ?array $meta = null,
     ): self {
-        $this->prompts[] = compact('handler', 'name', 'description', 'icons', 'meta');
+        $this->prompts[] = compact('handler', 'name', 'title', 'description', 'icons', 'meta');
 
         return $this;
     }