create RequestHandlerInterface

composer.json

@@ -4,7 +4,8 @@
     "type": "library",
     "require": {
         "php": "^8.5",
-        "psr/http-message": "^2.0"
+        "psr/http-message": "^2.0",
+        "psr/http-server-handler": "^1.0"
     },
     "license": "MIT",
     "autoload": {

src/Potter/Request/RequestHandlerInterface.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Potter\Request;
+
+use \Psr\Http\Message\ResponseInterface as PsrResponseInterface;
+use \Psr\Http\Server\RequestHandlerInterface as PsrRequestHandlerInterface;
+use \Psr\Http\Message\ServerRequestInterface as PsrServerRequestInterface;
+
+interface RequestHandlerInterface extends PsrRequestHandlerInterface
+{
+    public function handle(PsrServerRequestInterface $request): PsrResponseInterface;
+}