swap-stack: slot KV save/restore for duo prompt caches (x570 S5 pattern)

--slot-save-path + --cache-reuse 256 on both duo members, ./kv-cache
mounted at /cache. Measured on ornith (3K-token system prompt): warm
prefix reuse 296ms vs 106.7s cold prefill (361x); slot save 84MB in
59ms, GDN recurrent state serializes. scripts/duo-warmboot.sh wraps
save/restore/status via llama-swap /upstream passthrough. Restore
after restart: run 'duo-warmboot.sh restore' post stack boot.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

swap-stack/config.yaml

@@ -71,6 +71,7 @@ models:
       --ctx-size 131072
       --batch-size 1024 --ubatch-size 512
       --cont-batching --parallel 1
+      --slot-save-path /cache/ornith-duo --cache-reuse 256
     ttl: 0
 
   "qwen3-4b-duo":
@@ -86,6 +87,7 @@ models:
       --ctx-size 24576
       --batch-size 512 --ubatch-size 256
       --cont-batching --parallel 1
+      --slot-save-path /cache/qwen-duo --cache-reuse 256
     ttl: 0
 
   # ── MoE offload models (2026-07-10) ────────────────────────────────────────