minor #721 [OpenAI] Add Agent-as-Tool example (OskarStark)

This PR was squashed before being merged into the main branch.

Discussion
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[OpenAI] Add Agent-as-Tool example

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Docs?         | no
| Issues        | --
| License       | MIT

### Proof
<img width="1950" height="578" alt="CleanShot 2025-10-02 at 15 49 31@2x" src="https://github.com/user-attachments/assets/77c08aa7-701d-47c4-a127-f4c438c891cb" />

Commits
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bee0151 [OpenAI] Add Agent-as-Tool example

Author: OskarStark

examples/openai/agent-as-tool.php

@@ -0,0 +1,58 @@
+<?php
+
+/*
+ * This file is part of the Symfony package.
+ *
+ * (c) Fabien Potencier <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+use Symfony\AI\Agent\Agent;
+use Symfony\AI\Agent\InputProcessor\SystemPromptInputProcessor;
+use Symfony\AI\Agent\Toolbox\AgentProcessor;
+use Symfony\AI\Agent\Toolbox\Tool\Agent as AgentTool;
+use Symfony\AI\Agent\Toolbox\ToolFactory\ChainFactory;
+use Symfony\AI\Agent\Toolbox\ToolFactory\MemoryToolFactory;
+use Symfony\AI\Agent\Toolbox\ToolFactory\ReflectionToolFactory;
+use Symfony\AI\Agent\Toolbox\Toolbox;
+use Symfony\AI\Platform\Bridge\OpenAi\PlatformFactory;
+use Symfony\AI\Platform\Message\Message;
+use Symfony\AI\Platform\Message\MessageBag;
+
+require_once dirname(__DIR__).'/bootstrap.php';
+
+$platform = PlatformFactory::create(env('OPENAI_API_KEY'), http_client());
+
+// Create a specialized agent for mathematical calculations
+$mathSystemPrompt = new SystemPromptInputProcessor('You are a mathematical calculator. When given a math problem, solve it and return only the numerical result with a brief explanation.');
+$mathAgent = new Agent($platform, 'gpt-4o', [$mathSystemPrompt], logger: logger());
+
+// Wrap the math agent as a tool
+$mathTool = new AgentTool($mathAgent);
+
+// Use MemoryToolFactory to register the tool with metadata
+$memoryFactory = new MemoryToolFactory();
+$memoryFactory->addTool(
+    $mathTool,
+    'calculate',
+    'Performs mathematical calculations. Use this when you need to solve math problems or do arithmetic.',
+);
+
+// Combine with ReflectionToolFactory using ChainFactory
+$chainFactory = new ChainFactory([
+    $memoryFactory,
+    new ReflectionToolFactory(),
+]);
+
+// Create the main agent with the math agent as a tool
+$toolbox = new Toolbox([$mathTool], toolFactory: $chainFactory, logger: logger());
+$processor = new AgentProcessor($toolbox);
+$agent = new Agent($platform, 'gpt-4o-mini', [$processor], [$processor], logger: logger());
+
+// Ask a question that requires mathematical calculation
+$messages = new MessageBag(Message::ofUser('I have 15 apples and I want to share them equally among 4 friends. How many apples does each friend get and how many are left over?'));
+$result = $agent->call($messages);
+
+echo $result->getContent().\PHP_EOL;