### CrawlerContext (`CrawlerContext.java`)

Execution context and configuration.

**Important Fields**:
```java
String sessionId                // Format: yyyyMMddHHmmssSSS
volatile CrawlerStatus status   // DONE, RUNNING
AtomicLong accessCount          // Thread-safe counter
int numOfThread = 10            // Crawler threads
int maxDepth = -1               // Max depth (-1 = unlimited)

     */
    public Crawler() {
        crawlerContext = new CrawlerContext();
        final SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMddHHmmssSSS", Locale.ENGLISH);
        crawlerContext.sessionId = sdf.format(new Date());
    }

    /**
     * Adds a URL to the crawling queue.
     * @param url The URL to add.
     */

    /** Date format pattern for document index suffix generation. */
    public static final String DOCUMENT_INDEX_SUFFIX_PATTERN = "yyyyMMddHHmmssSSS";

    // ============================================================
    // System Property Keys
    // ============================================================