[Server] Keep injectable parameters out of the published inputSchema (#482)

src/Capability/Registry/InjectableParameters.php

@@ -0,0 +1,63 @@
+<?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\Capability\Registry;
+
+use Mcp\Server\ClientGateway;
+use Mcp\Server\RequestContext;
+
+/**
+ * Single source of truth for handler parameter types the SDK injects itself.
+ *
+ * Both schema generation (which must exclude these parameters from the
+ * published inputSchema) and argument preparation (which must inject them)
+ * read this list, so the two cannot drift apart.
+ *
+ * @internal
+ */
+final class InjectableParameters
+{
+    private const TYPES = [
+        RequestContext::class,
+        ClientGateway::class,
+    ];
+
+    private function __construct()
+    {
+    }
+
+    public static function supports(string $typeName): bool
+    {
+        foreach (self::TYPES as $type) {
+            if (is_a($typeName, $type, true)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * @param array<string, mixed> $arguments the raw argument bag including the internal "_session" and "_request" entries
+     */
+    public static function resolve(string $typeName, array $arguments): ?object
+    {
+        if (RequestContext::class === $typeName && isset($arguments['_session'], $arguments['_request'])) {
+            return new RequestContext($arguments['_session'], $arguments['_request']);
+        }
+
+        if (ClientGateway::class === $typeName && isset($arguments['_session'])) {
+            return new ClientGateway($arguments['_session']);
+        }
+
+        return null;
+    }
+}