nx_avail_map_gate.nx

nx_avail_map_gate.nx -- KAT + negative controls for the shared cross-peer availability map. Native sovereign lane; exit 0 = all pass, N = assertion N failed. Prints every MEASURED value (no self-grading -- the raw counts/picks are the evidence). T1 cross-peer count aggregation is exact T2 rarest-first picks the globally-rarest piece the peer HAS T3 rarest-first advances to the next-rarest once a piece is done T4 NEG-CONTROL: a peer that LACKS the rarest pieces is never told to fetch them T5 a HAVE message bumps a single piece's availability T6 NEG-CONTROL: the lock is load-bearing -- 8 procs x 20 locked increments == exact, the same UNLOCKED loses counts (torn read-modify-write)