// StringExtBox: small helpers that make scripts concise
static box StringExtBox {
  trim(s) {
    // naive: trim spaces and newlines at both ends
    local i = 0
    local j = s.length()
    loop (i < j) {
      local ch = s.substring(i, i+1)
      if ch == " " || ch == "\n" || ch == "\r" || ch == "\t" { i = i + 1 } else { break }
    }
    loop (j > i) {
      local ch2 = s.substring(j-1, j)
      if ch2 == " " || ch2 == "\n" || ch2 == "\r" || ch2 == "\t" { j = j - 1 } else { break }
    }
    return s.substring(i, j)
  }
  startsWith(s, pref) {
    return s.substring(0, pref.length()) == pref
  }
  endsWith(s, suf) {
    local n = s.length()
    local m = suf.length()
    if m > n { return false }
    return s.substring(n-m, n) == suf
  }
  replace(s, old, neu) {
    // naive single replacement (first occurrence)
    local i = s.indexOf(old)
    if i < 0 { return s }
    return s.substring(0, i) + neu + s.substring(i + old.length(), s.length())
  }
  split(s, delim) {
    // minimal split (no regex). returns ArrayBox of parts
    local out = []
    local pos = 0
    local dlen = delim.length()
    loop (true) {
      local idx = s.indexOf(delim)
      if idx < 0 { out.push(s)  break }
      out.push(s.substring(0, idx))
      s = s.substring(idx + dlen, s.length())
    }
    return out
  }
}