ars-backend/app/Services/ContextBuilder.php

<?php

namespace App\Services;

use App\Models\Message;
use App\Services\Agent\AgentContext;
use Illuminate\Support\Collection;

class ContextBuilder
{
    public function __construct(private readonly int $limit = 20)
    {
    }

    public function build(string $sessionId, string $runId): AgentContext
    {
        $messages = $this->loadRecentMessages($sessionId);

        logger('context builder loaded messages', [
            'session_id' => $sessionId,
            'run_id' => $runId,
            'message_count' => $messages->count(),
            'message_types' => $messages->pluck('type', 'seq')->toArray(),
        ]);

        return new AgentContext(
            $runId,
            $sessionId,
            'You are an agent inside ARS. Respond concisely in markdown format. Use the following conversation context.',
            $messages->map(function (Message $message) {
                return [
                    'message_id' => $message->message_id,
                    'role' => $message->role,
                    'type' => $message->type,
                    'content' => $message->content,
                    'payload' => $message->payload,
                    'seq' => $message->seq,
                ];
            })->values()->all()
        );
    }

    private function loadRecentMessages(string $sessionId): Collection
    {
        return Message::query()
            ->where('session_id', $sessionId)
            ->whereIn('role', [Message::ROLE_USER, Message::ROLE_AGENT, Message::ROLE_TOOL])
            ->whereIn('type', ['user.prompt', 'agent.message', 'tool.call', 'tool.result'])
            ->orderByDesc('seq')
            ->limit($this->limit)
            ->get()
            ->sortBy('seq')
            ->values();
    }
}