frank-primary: pin the expert host region to 120 GiB (--expert-offload-mem)

The host region was the ONE arena-plan term still autofitting per boot: with
no cap the planner binds it to MemAvailable AT BOOT minus PLE/process/api/
margin terms (boot 2026-10-05: 237.97 GiB -> 159.39 GiB usable; the same host
reads 75.4 GiB available while running). Demand is 105.48 GiB
(52.74/rank x 2 ranks, 23,040 swap-target experts); a boot where co-tenant
RAM squeezed the bound near that silently pins next-hottest experts VRAM-only
(pinned_extra warning, smaller swap region, no flag change). 120 GiB =
measured demand + 14% headroom on 246.1 GiB total. Semantics verified in the
shipped image: cap binds as the bound, exceedance only warns.

The GPU-side arena is unchanged (deterministic arithmetic over the same
constants): verify after boot that host reads '--expert-offload-mem' and
slots stay 7,762. Seam: red first (wiring + value), then green; full suite
368+1 green.

scripts/frank-primary.env

@@ -213,6 +213,22 @@ FRANK_PRIMARY_UTIL=0.982
 FRANK_PRIMARY_CUDAGRAPH_BASE_MB=0
 FRANK_PRIMARY_CUDAGRAPH_PER_GRAPH_MB=12
 
+# HOST-region cap — the last arena-plan term that still autofit per boot. With
+# no cap the planner's host bound is MemAvailable AT BOOT minus PLE 47.68 -
+# 2 x 7.0 process - 5.0 api/engine - 5% margin (measured boot 2026-10-05:
+# MemAvailable 237.97 -> 159.39 GiB usable across 2 ranks; the demand is 105.48
+# = 52.74/rank x 2 ranks, 23,040 swap-target experts). The same host reads 75.4
+# GiB available while running — the bound tracks whatever the co-tenants hold at
+# boot, and a boot where that drops near the demand silently pins next-hottest
+# experts VRAM-only instead (smaller swap region; the pinned_extra warning is
+# the only trace). Pin 120 GiB: measured demand + 14% headroom, on a host with
+# 246.1 GiB total. If a boot ever logs "expert-offload-mem … exceeds
+# MemAvailable at plan time", THAT is the contract being broken — look at the
+# co-tenant RAM before touching this number. Plan semantics verified in the
+# shipped image (offloader/expert_plan.py): the cap binds as the bound, an
+# exceedance only warns.
+FRANK_PRIMARY_EXPERT_OFFLOAD_MEM=120
+
 # --- optional engine knobs (unset == the flag is absent) ---------------------
 # FRANK_PRIMARY_SPEC holds the WHOLE --speculative-config JSON; setting it adds
 # the flag. THE RETIREMENT VERDICT WAS INVALID: c1248d4 (2026-10-02) retired MTP

scripts/serve-frank-primary.sh

@@ -156,6 +156,7 @@ podman run -d --name "$FRANK_PRIMARY_CONTAINER" \
   --max-num-seqs "$FRANK_PRIMARY_SEQS" \
   ${FRANK_PRIMARY_MNBT:+--max-num-batched-tokens "$FRANK_PRIMARY_MNBT"} \
   ${FRANK_PRIMARY_PRECISE_MEMORY:+--expert-precise-memory} \
+  ${FRANK_PRIMARY_EXPERT_OFFLOAD_MEM:+--expert-offload-mem "$FRANK_PRIMARY_EXPERT_OFFLOAD_MEM"} \
   --gpu-memory-utilization "$FRANK_PRIMARY_UTIL" \
   --kv-cache-memory-bytes "$FRANK_PRIMARY_KV_BYTES" \
   --kv-cache-dtype "$FRANK_PRIMARY_KV_DTYPE" \