main: 引入 AgentProvider 流式事件与 OpenAI 兼容适配

- 增加流式事件流支持，Provider 输出 `message.delta` 等事件
- 实现 OpenAI 兼容适配器，包括 RequestBuilder、ApiClient 等模块
- 更新 Agent Run 逻辑，支持流式增量写入与模型完成状态管理
- 扩展配置项 `agent.openai.*`，支持模型、密钥等配置
- 优化文档，完善流式事件与消息类型说明
- 增加单元测试，覆盖 Provider 和 OpenAI 适配相关逻辑
- 更新环境变量与配置示例，支持新功能

app/Services/Agent/OpenAi/OpenAiEventNormalizer.php

@@ -0,0 +1,50 @@
+<?php
+
+namespace App\Services\Agent\OpenAi;
+
+use App\Services\Agent\ProviderEvent;
+
+class OpenAiEventNormalizer
+{
+    /**
+     * Normalizes a single SSE payload into ProviderEvent values.
+     *
+     * @return array<int, ProviderEvent>
+     */
+    public function normalize(string $payload): array
+    {
+        if (trim($payload) === '[DONE]') {
+            return [ProviderEvent::done('done')];
+        }
+
+        $decoded = json_decode($payload, true);
+
+        if (! is_array($decoded)) {
+            return [ProviderEvent::error('INVALID_JSON', 'Agent provider returned invalid JSON', [
+                'raw' => $payload,
+            ])];
+        }
+
+        $events = [];
+        $choices = $decoded['choices'] ?? [];
+        $firstChoice = is_array($choices) ? ($choices[0] ?? null) : null;
+        $delta = is_array($firstChoice) ? ($firstChoice['delta'] ?? null) : null;
+
+        if (is_array($delta)) {
+            $content = $delta['content'] ?? null;
+            if (is_string($content) && $content !== '') {
+                $events[] = ProviderEvent::messageDelta($content);
+            }
+        }
+
+        if (is_array($firstChoice) && array_key_exists('finish_reason', $firstChoice) && $firstChoice['finish_reason'] !== null) {
+            $events[] = ProviderEvent::done((string) $firstChoice['finish_reason']);
+        }
+
+        if (isset($decoded['usage']) && is_array($decoded['usage'])) {
+            $events[] = ProviderEvent::usage($decoded['usage']);
+        }
+
+        return $events;
+    }
+}