[Hakkin]

Ah, I think I understand the random bytes at the start of the script now. They're prepended to make the partial output of the "corrupted" (pre-tr'd) test stream look like random data. Without those random bytes, you will see part of the start of the script if you observe the partially decompressed output before xz throws an error. They really thought quite carefully about hiding this well.

Still not sure about the repeated lines, though now I'm convinced there must be some reason for it.