K-grouping: host fixes land 24x -> 9.7x; batched drain a measured negative; dispatch now 78%
K-grouping: A/B confirms the mcc fix — grouped path 24x -> 12x, both arm orders; over-allocation is NOT the next term
K-grouping cost on RK3588: the 23.6x is host-side, not hardware; CACC ruled out; clip search beats g128