DL-417
ControlAck carries out-of-order applied seqs as inclusive runs packed as flat [start, end, ...] pairs (repeated uint64 applied_above_ranges = 3), one pair per run, so the ack is O(runs); the per-seq applied_above stays read-only for older agents, and the Runner prunes by testing retained seqs against the ranges, never expanding them
Status: Active (Matt, 2026-07-26)