backup_world() {
  echo "[backup] backing up world directory..."
  ts=$(date +"%Y-%m-%d_%H-%M-%S")
  mkdir -p "${BACKUPDIR}"

  world_dir="${UNITY3D_WORLDS}/worlds_local/${WORLD_NAME}"

  if [ -d "${world_dir}" ]; then
    zip -r "${BACKUPDIR}/${WORLD_NAME}_${ts}.zip" "${world_dir}"
    echo "[backup] created ${BACKUPDIR}/${WORLD_NAME}_${ts}.zip"
  else
    echo "[backup] WARNING: world directory not found: ${world_dir}"
  fi
}