Gemini structured output fails with includeThoughts: true

[fobtastic]

Description

When using Gemini's structured output with includeThoughts: true, the response fails to parse because Prism's Structured.php handler doesn't filter out thought parts like the Text.php handler does.

Steps to Reproduce

use Prism\Prism\Facades\Prism;
use Prism\Prism\Enums\Provider;
use Prism\Prism\Schema\ObjectSchema;
use Prism\Prism\Schema\StringSchema;

$schema = new ObjectSchema(
    name: 'test',
    properties: [
        new StringSchema('result', 'A result')
    ]
);

$response = Prism::structured()
    ->using(Provider::Gemini, 'gemini-2.0-flash-exp')
    ->withSystemPrompt('Extract information')
    ->withPrompt('Test input')
    ->withSchema($schema)
    ->withProviderOptions([
        'thinkingConfig' => [
            'thinkingLevel' => 'low',
            'includeThoughts' => true,
        ],
    ])
    ->asStructured();

Expected Behavior

The structured output should be extracted from the actual content part (the non-thought part), similar to how Text.php handles it.

Actual Behavior

Error: Structured object could not be decoded. Received: **Thinking Through...

The response contains the thinking text instead of the JSON because Prism reads from parts[0].text, which contains the thinking when includeThoughts: true.

Root Cause

When includeThoughts: true, Gemini returns multiple parts:

• parts[0]: { thought: true, text: "thinking content..." }
• parts[1]: { thought: false, text: "{\"result\":\"...\"}" }

Currently in src/Providers/Gemini/Handlers/Structured.php, the code always reads from parts[0]:

$responseMessage = new AssistantMessage(
    data_get($data, 'candidates.0.content.parts.0.text') ?? '',
    // ...
);

And in addStep():

structured: $isStructuredStep ? $this->extractStructuredData(data_get($data, 'candidates.0.content.parts.0.text') ?? '') : [],

Proposed Fix

The Structured.php handler should filter parts similar to how Text.php does:

protected function extractTextContent(array $data): string
{
    $parts = data_get($data, 'candidates.0.content.parts', []);
    $textParts = [];

    foreach ($parts as $part) {
        // Only include text from parts that are NOT thoughts
        if (isset($part['text']) && (!isset($part['thought']) || $part['thought'] === false)) {
            $textParts[] = $part['text'];
        }
    }

    return implode('', $textParts);
}

Additionally, it would be valuable to extract and expose the thought content separately (similar to how Text.php extracts thoughtSummaries), so developers can access the reasoning for debugging purposes.

Workaround

Set includeThoughts: false (or omit it entirely) to avoid the issue. The model will still use thinking internally, but the thought content won't be included in the response.

Environment

• Prism version: 0.99.2
• Provider: Gemini
• Model: gemini-3.0-flash-preview (Gemini Flash 3 with thinking support)