The replay law named `--checkpoint-policy floor`; config.cpp admits exactly
geometric-backoff (default), tip-only, keep-all and refuses anything else at
boot, so the recorded arm could never be deployed. Replaced with the real
semantics, priced from core/mem/prefix.{h,cpp}: the default keeps a geometric
ladder (9 snapshots for a 200k session at interval 2048 -- exactly the live
ledger line -- so a turn diverging d behind the tip can resume at tip-3d:
diverge at 120k, replay 21.7k); retention is not the write path, so keep-all
buys a bounded replay for pinned host RAM alone (196 slots x 111.98 MiB = 21.4
GiB against the store's eighth-of-host budget of 31.5 GiB, hard bound = room);
and shortening --checkpoint-interval cannot fix the deep case -- the coarsest
ladder scale is interval x 2^k under the depth, so the deepest gap stays about
half the prompt at every interval. §9 keeps only the three-name locator.