* </p>
 *
 * <p>
 * The handler relies on environment variables for configuration:
 * </p>
 * <ul>
 *   <li>{@code GCS_PROJECT_ID}: The Google Cloud project ID.</li>
 *   <li>{@code GCS_ENDPOINT}: Custom endpoint URL (optional, for testing with fake-gcs-server).</li>
 *   <li>{@code GCS_CREDENTIALS_FILE}: Path to service account JSON file (optional).</li>
 * </ul>
 *
 * <p>