Empirical (300, clip 00042): base .m2ts (1567 extents, 25.85 GB) is entirely
inside the SSIF LBA span; dependent = SSIF − base = 1567 ranges, 9.59 GB
(exact vs 35.43−25.85). 200/200 sampled dependent-view units decrypt under the
base UK. => de-interleave needs no SSIF parsing (complement of the base extents
we already resolve), and the dependent eye needs no extra key.
