def merge(spans):
    """Merge overlapping or touching [start, end] spans, in any order."""
    if not spans:
        return []
    ordered = sorted(spans, key=lambda s: (s[0], s[1]))
    out = [list(ordered[0])]
    for start, end in ordered[1:]:
        last = out[-1]
        if start <= last[1]:
            last[1] = max(last[1], end)
        else:
            out.append([start, end])
    return [tuple(s) for s in out]