[Agent] Fix sources metadata unavailable during streaming

[Copilot]

Q	A
Bug fix?	yes
New feature?	no
Docs?	no
Issues	Fix #833
License	MIT

• Analyze the issue with sources metadata being null during streaming
• Identify the root cause in ToolboxStreamResult
• Implement fix to propagate metadata from inner result to outer result
• Add test for streaming with sources
• Fix trailing whitespace in test (code quality)
• Fix "yield from" error with non-iterable content
• Simplify content type check for better maintainability
• Improve code comments and comparison consistency
• Add safety check for non-iterable objects
• Revert unnecessary .gitignore change
• Apply Symfony code style conventions

Summary

Fixed issue where sources metadata was inaccessible when using streaming with the Agent. The problem was that metadata was set on the inner result but never propagated to the outer StreamResult object.

Changes:

• Modified StreamResult::getContent() to capture and propagate metadata from inner result
• Added comprehensive type checking to safely handle all content types
• Added test testSourcesEndUpInResultMetadataWithStreaming() to verify the fix works correctly
• Applied Symfony code style conventions (Yoda conditions, fully qualified function names)

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Agent] Unable to access sources metadata with streaming</issue_title>
<issue_description>I am implementing the Symfony AI Agent in combination with the ai-sdk. I want to display the used sources in the UI, so I want to dispatch these in an event stream using the ai-sdk Data Stream Protocol. However, during streaming, the metadata seems to reset and sources are always null. Without the stream option this works fine.

Should this be done in a different order? The sources are present at some point, but seem to reset while actually streaming the content back.

This is basically all that I am doing:

    public function __invoke(ChatRequest $request): StreamedResponse
    {
        $platform = PlatformFactory::create(env('OPENAI_API_KEY'), HttpClient::create());
        
        $toolBox = new ToolBox([
            new RandomTool(),
        ]);
        $processor = new AgentProcessor($toolBox, includeSources: true);
        $agent = new Agent($platform, 'gpt-4o-mini', [$processor], [$processor]);

        $messages = new MessageBag();
        foreach ($request->messages() as $message) {
            foreach ($message['parts'] as $part) {
                if ($part['type'] !== 'text') {
                    continue;
                }
                $messages->add(Message::ofUser($part['text']));
            }
        }

        $result = $agent->call($messages, [
            'stream' => true
        ]);

        $response = new StreamedResponse(function () use ($result) {
            $messageId = 'msg_' . bin2hex(random_bytes(16));
            $textBlockId = 'text_' . bin2hex(random_bytes(16));
            
            $this->sendSSE(['type' => 'start', 'messageId' => $messageId]);
            $this->sendSSE(['type' => 'text-start', 'id' => $textBlockId]);
            
            foreach ($result->getContent() as $chunk) {
                $text = (string)$chunk;
                if ($text !== '') {
                    $this->sendSSE([
                        'type' => 'text-delta',
                        'id' => $textBlockId,
                        'delta' => $text
                    ]);
                }
            }
            
            $this->sendSSE(['type' => 'text-end', 'id' => $textBlockId]);
            
            // This is always null
            $sources = $result->getMetadata()->get('sources', []);
            foreach ($sources as $source) {
                if (!$source instanceof Source) {
                    continue;
                }
                $this->sendSSE([
                    'type' => 'source-url',
                    'sourceId' => $source->getReference(),
                    'url' => $source->getReference(),
                    'title' => $source->getName()
                ]);
            }
            
            $this->sendSSE(['type' => 'finish']);
            
            echo "data: [DONE]\n\n";
            flush();
        });

        
        $response->headers->set('Content-Type', 'text/event-stream');
        $response->headers->set('Cache-Control', 'no-cache');
        $response->headers->set('Connection', 'keep-alive');
        $response->headers->set('X-Accel-Buffering', 'no');
        $response->headers->set('x-vercel-ai-ui-message-stream', 'v1');
        
        return $response;
    }

    private function sendSSE(array $data): void
    {
        echo 'data: ' . json_encode($data, JSON_UNESCAPED_UNICODE) . "\n\n";
        flush();
    }

</issue_description>

<agent_instructions>Try to fix this issue. do it as minimal as possible</agent_instructions>

Comments on the Issue (you are @copilot in this section)

@chr-hertel Sounds like a legit bug to me - didn't test that yet as well. PR ofc welcome :)

• Fixes [Agent] Unable to access sources metadata with streaming #833

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[OskarStark]

@copilot fix the CI

[JorrinKievit]

I checked and this indeed fixed it! @OskarStark