Add elicitation support for server-to-client user input requests (#228)

- Add ElicitAction enum (accept/decline/cancel)
- Add schema definitions for elicitation fields (string, number, boolean, enum)
- Add ElicitationSchema wrapper for requestedSchema
- Add ElicitRequest and ElicitResult for elicitation/create method
- Update ClientCapabilities to support elicitation capability
- Add elicit() method to ClientGateway
- Store client capabilities in session during initialization
- Add comprehensive unit tests
- Add elicitation example server with book_restaurant, confirm_action, and collect_feedback tools

tests/Unit/Schema/Elicitation/BooleanSchemaDefinitionTest.php

@@ -0,0 +1,110 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * 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\Tests\Unit\Schema\Elicitation;
+
+use Mcp\Exception\InvalidArgumentException;
+use Mcp\Schema\Elicitation\BooleanSchemaDefinition;
+use PHPUnit\Framework\TestCase;
+
+final class BooleanSchemaDefinitionTest extends TestCase
+{
+    public function testConstructorWithMinimalParams(): void
+    {
+        $schema = new BooleanSchemaDefinition('Confirm');
+
+        $this->assertSame('Confirm', $schema->title);
+        $this->assertNull($schema->description);
+        $this->assertNull($schema->default);
+    }
+
+    public function testConstructorWithAllParams(): void
+    {
+        $schema = new BooleanSchemaDefinition(
+            title: 'Confirmation',
+            description: 'Do you confirm this action?',
+            default: false,
+        );
+
+        $this->assertSame('Confirmation', $schema->title);
+        $this->assertSame('Do you confirm this action?', $schema->description);
+        $this->assertFalse($schema->default);
+    }
+
+    public function testConstructorWithTrueDefault(): void
+    {
+        $schema = new BooleanSchemaDefinition(
+            title: 'Subscribe',
+            default: true,
+        );
+
+        $this->assertTrue($schema->default);
+    }
+
+    public function testFromArrayWithMinimalParams(): void
+    {
+        $schema = BooleanSchemaDefinition::fromArray(['title' => 'Confirm']);
+
+        $this->assertSame('Confirm', $schema->title);
+        $this->assertNull($schema->description);
+        $this->assertNull($schema->default);
+    }
+
+    public function testFromArrayWithAllParams(): void
+    {
+        $schema = BooleanSchemaDefinition::fromArray([
+            'title' => 'Confirmation',
+            'description' => 'Do you confirm this action?',
+            'default' => true,
+        ]);
+
+        $this->assertSame('Confirmation', $schema->title);
+        $this->assertSame('Do you confirm this action?', $schema->description);
+        $this->assertTrue($schema->default);
+    }
+
+    public function testFromArrayWithMissingTitle(): void
+    {
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Missing or invalid "title"');
+
+        /* @phpstan-ignore argument.type */
+        BooleanSchemaDefinition::fromArray([]);
+    }
+
+    public function testJsonSerializeWithMinimalParams(): void
+    {
+        $schema = new BooleanSchemaDefinition('Confirm');
+
+        $this->assertSame([
+            'type' => 'boolean',
+            'title' => 'Confirm',
+        ], $schema->jsonSerialize());
+    }
+
+    public function testJsonSerializeWithAllParams(): void
+    {
+        $schema = new BooleanSchemaDefinition(
+            title: 'Confirmation',
+            description: 'Do you confirm this action?',
+            default: false,
+        );
+
+        $this->assertSame([
+            'type' => 'boolean',
+            'title' => 'Confirmation',
+            'description' => 'Do you confirm this action?',
+            'default' => false,
+        ], $schema->jsonSerialize());
+    }
+}