Function set_decode_ring_slots 

pub fn set_decode_ring_slots(slots: usize) -> usize

Publish the decode-ring depth. Returns the value in force (first write wins, matching gdn_flags::set_from_cli): an explicit --ssm-decode-ring-slots N is published before preflight runs, so the auto-fit’s later write is a no-op and an operator’s explicit depth is never silently shrunk.