│   └── service/             # Core services
├── fess-crawler-lasta/       # LastaFlute DI integration
└── fess-crawler-opensearch/  # OpenSearch backend
```

### Key Components

#### Core Engine
- **Crawler**: Main orchestrator managing crawl execution
- **CrawlerContext**: Execution context and configuration
- **CrawlerThread**: Individual crawler thread implementation

#### Client Architecture

import org.opensearch.common.unit.TimeValue;
import org.opensearch.core.action.ActionListener;
import org.opensearch.core.action.ActionResponse;
import org.opensearch.index.IndexNotFoundException;
import org.opensearch.index.engine.VersionConflictEngineException;
import org.opensearch.index.query.QueryBuilder;
import org.opensearch.search.Scroll;
import org.opensearch.search.SearchHit;
import org.opensearch.threadpool.ThreadPool;