The naive bound `lba + count > r.count` wraps for an lba near u64 max: the
sum overflows to a small value, sails under the check, and `base + lba`
wraps to an absolute block OUTSIDE the range. Calibrated, it is a real
confinement escape — a process confined to [1,3) reads absolute block 0
(the boot sector) with lba = maxInt(u64), since base + lba wraps to 0.
The bound is rewritten as two subtractions that cannot overflow: lba within
the range, and count within what remains. block-range gains a wrap-refused
assertion calibrated to be exploitable against the naive form — it FAILS
against the old bound (reads block 0) and passes against the fix (verified
by reverting the clamp). Caught pre-emptively before the V2 boundary review.
Daniel Samson
89d4592777