feat(frank-archon): move the endpoint to radiance 1.8.1 and its budget model

The decode stall is step contention (measured: 18.7 ms decode-only steps
against 317 ms steps that carry a prefill chunk, decode at 13 t/s median
while prefill runs), and the two engine knobs that fix it arrived after this
endpoint's pin. Moving to 1.8.1 (2026-10-18) brings both, and brings two CLI
breaks with them:

  - --vram-weights-mib / --vram-kv-mib were REMOVED at 1.3.0. The per-card
    split between the expert slab and the KV pool is now derived by the
    engine's budget resolver from --gpu-headroom-mib, the cache bound
    (--max-model-len, --max-num-seqs) and --host-pool-mib, and the cache may
    lend idle blocks to the expert slab. The slab size and the pool's token
    count are boot-ledger lines from here on, so the capacity contract
    (3 x 200,000 fp8) is verified live by the probe's capacity leg instead of
    computed from an env number.
  - The prefix cache has no disk tier any more: --prefix-cache-dir and
    --prefix-cache-disk-mib are refusals and --prefix-cache-host-mib is
    --prefix-cache-mib. 64 GiB of parked KV on NVMe becomes re-prefill, so
    prefix_hit_rate is the thing to watch after this boot.

env: image re-pinned to the 1.8.1 digest; the pair and the disk tier dropped;
FRANK_ARCHON_PREFIX_CACHE_MIB replaces the host/disk pair; new
FRANK_ARCHON_BUSY_PREFILL_CHUNK=auto (explicit, because auto vs off is the
difference between decode waiting one chunk and waiting a whole step) and
FRANK_ARCHON_PREFILL_INTERLEAVE=0 (opt-in through a guarded argv array).

serve: argv follows the new CLI, /data mount and the pre-created kvcache path
go with the disk tier, and the retired env keys are no longer required (they
would abort ExecStart). autoresearch-frank-archon.sh takes the same CLI, with
a cold prefill now coming from --prefix-cache-mib 0 instead of a per-run disk
directory. run-swift15-bf16.sh is untouched: it pins its own engines by design.

tests: the two budget-arithmetic seams asserted knobs that no longer exist and
are replaced by one seam that asserts the retired knobs are ABSENT from env and
argv - a stale line is a boot refusal, not a no-op. The container-contract seam
now asserts the tune mount and the absence of /data.

scripts/autoresearch-frank-archon.sh

@@ -29,10 +29,10 @@
 # The scratch mirrors the production container contract exactly (serve-frank-
 # primary.sh): --network host, --init, seccomp=unconfined (io_uring for the
 # n-gram table), memlock unbounded (the ~132 GiB pinned ledger), /dev/kfd +
-# /dev/dri, the .rad ro, the state dir rw, the tune cache mount. The ONLY
-# differences: the container name (arbench, so prod's identity is untouched)
-# and a FRESH prefix-cache disk tier (arbench/, wiped per run) so the cold
-# prefill is cold — the prod tier at kvcache/frank-archon is left intact.
+# /dev/dri, the .rad ro, the tune cache mount. The ONLY differences: the
+# container name (arbench, so prod's identity is untouched) and the prefix cache
+# switched OFF (--prefix-cache-mib 0), so every prefill is cold — the tier is
+# host RAM now, there is no per-run disk directory to wipe.
 set -uo pipefail
 
 ENV_FILE="${1:-/home/dank/serverAppConfigs/scripts/frank-archon.env}"
@@ -60,9 +60,8 @@ set -a; . "$ENV_FILE"; set +a
 sudo systemctl stop frank-archon >/dev/null 2>&1 || true
 podman rm -f "$SCRATCH" >/dev/null 2>&1 || true
 
-# --- fresh prefix-cache tier for a cold prefill (prod's tier untouched) ------
-FRESH_KV="$FRANK_ARCHON_STATE_DIR/kvcache/$SCRATCH"
-rm -rf "$FRESH_KV"; mkdir -p "$FRESH_KV"
+# --- the prefix cache is switched off below, so there is no scratch KV tree ---
+# to wipe; the cold prefill comes from --prefix-cache-mib 0.
 mkdir -p "$FRANK_ARCHON_STATE_DIR/tune"
 
 # --- boot the scratch: the production run line, scratch name + fresh KV ------
@@ -73,7 +72,6 @@ podman run -d --name "$SCRATCH" \
   --ulimit memlock=-1:-1 \
   --device /dev/kfd --device /dev/dri \
   -v "$FRANK_ARCHON_MODEL_DIR":/models:ro \
-  -v "$FRANK_ARCHON_STATE_DIR":/data \
   -v "$FRANK_ARCHON_STATE_DIR/tune":/opt/radiance/share/radiance/tune \
   -v "$FRANK_ARCHON_TEMPLATE":/templates/template.jinja:ro \
   "$FRANK_ARCHON_IMAGE" \
@@ -87,12 +85,9 @@ podman run -d --name "$SCRATCH" \
   --placement "$FRANK_ARCHON_PLACEMENT" \
   --host-pool-mib "$FRANK_ARCHON_HOST_POOL_MIB" \
   --gpu-headroom-mib "$FRANK_ARCHON_GPU_HEADROOM_MIB" \
-  --vram-weights-mib "$FRANK_ARCHON_VRAM_WEIGHTS_MIB" \
-  --vram-kv-mib "$FRANK_ARCHON_VRAM_KV_MIB" \
   --kv-cache-dtype "$FRANK_ARCHON_KV_DTYPE" \
-  --prefix-cache-host-mib "$FRANK_ARCHON_PREFIX_HOST_MIB" \
-  --prefix-cache-dir "/data/kvcache/$SCRATCH" \
-  --prefix-cache-disk-mib "$FRANK_ARCHON_PREFIX_DISK_MIB" \
+  --prefix-cache-mib 0 \
+  --busy-prefill-chunk "${FRANK_ARCHON_BUSY_PREFILL_CHUNK:-auto}" \
   --ngram-placement "$FRANK_ARCHON_NGRAM_PLACEMENT" \
   --num-speculative-tokens "$FRANK_ARCHON_SPEC_TOKENS" \
   --max-num-batched-tokens "$FRANK_ARCHON_MAX_BATCHED_TOKENS" \