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/serve-frank-archon.sh

@@ -15,12 +15,13 @@
 # log states every budget before anything is allocated (weights vs KV
 # split, the expert host pool's coverage of the worst case, the PLE pin,
 # the P2P answer per pair) — read it after every resize.
-# Deployed shape (2026-10-13): THREE decode slots x 200,000 tokens, fp8
-# (quantized) KV in a 5,120 MiB pool (contract 3 x 200,000 + 1.3 %) and a
-# 25,600 MiB resident expert slab — 30,720 MiB of the 30,969 MiB the engine's
-# own budget table makes claimable, spent on the slab because prefill is
-# slab-limited. 44 GiB/rank pinned expert pool, MTP depth 2, prefix cache host
-# 8 GiB + disk 64 GiB, PLE pinned in RAM.
+# Deployed shape (2026-10-19, radiance 1.8.1): THREE decode slots x 200,000
+# tokens, fp8 KV, 44 GiB/rank pinned expert pool, MTP depth 2, prefix cache in
+# pinned host RAM, PLE pinned in RAM. The per-card split between the expert slab
+# and the KV pool is NO LONGER an operator number — 1.3.0 removed the VRAM pair
+# and the budget resolver derives it from headroom, the cache bound and the host
+# pool, so the slab size and the pool's token count are LEDGER lines: after every
+# boot read them out of the log and check the pool still backs 3 x 200,000.
 #
 # The root unit (scripts/frank-archon.service, User=dank,
 # LimitMEMLOCK=infinity) grants the pin budget: 2 x 44 GiB expert pools +
@@ -56,13 +57,11 @@ set +a
 : "${FRANK_ARCHON_PLACEMENT:?FRANK_ARCHON_PLACEMENT must be set}"
 : "${FRANK_ARCHON_HOST_POOL_MIB:?FRANK_ARCHON_HOST_POOL_MIB must be set}"
 : "${FRANK_ARCHON_GPU_HEADROOM_MIB:?FRANK_ARCHON_GPU_HEADROOM_MIB must be set}"
-: "${FRANK_ARCHON_VRAM_WEIGHTS_MIB:?FRANK_ARCHON_VRAM_WEIGHTS_MIB must be set}"
-: "${FRANK_ARCHON_VRAM_KV_MIB:?FRANK_ARCHON_VRAM_KV_MIB must be set}"
+: "${FRANK_ARCHON_BUSY_PREFILL_CHUNK:?FRANK_ARCHON_BUSY_PREFILL_CHUNK must be set (auto|off|N)}"
 : "${FRANK_ARCHON_KV_DTYPE:?FRANK_ARCHON_KV_DTYPE must be set}"
 : "${FRANK_ARCHON_SPEC_TOKENS:?FRANK_ARCHON_SPEC_TOKENS must be set}"
 : "${FRANK_ARCHON_MAX_BATCHED_TOKENS:?FRANK_ARCHON_MAX_BATCHED_TOKENS must be set}"
-: "${FRANK_ARCHON_PREFIX_HOST_MIB:?FRANK_ARCHON_PREFIX_HOST_MIB must be set}"
-: "${FRANK_ARCHON_PREFIX_DISK_MIB:?FRANK_ARCHON_PREFIX_DISK_MIB must be set}"
+: "${FRANK_ARCHON_PREFIX_CACHE_MIB:?FRANK_ARCHON_PREFIX_CACHE_MIB must be set}"
 : "${FRANK_ARCHON_NGRAM_PLACEMENT:?FRANK_ARCHON_NGRAM_PLACEMENT must be set}"
 : "${FRANK_ARCHON_TTM_MIN_MIB:?FRANK_ARCHON_TTM_MIN_MIB must be set}"
 : "${FRANK_ARCHON_TTM_TARGET_MIB:?FRANK_ARCHON_TTM_TARGET_MIB must be set}"
@@ -103,19 +102,12 @@ if [ ! -f "$FRANK_ARCHON_TEMPLATE" ]; then
     exit 1
 fi
 
-mkdir -p "$FRANK_ARCHON_STATE_DIR/kvcache/frank-archon"
-# The engine's create is NOT recursive: with only the state dir mounted, its
-# "cannot create /data/kvcache/frank-archon: No such file or directory"
-# left the SSD prefix tier off (measured 2026-10-06 boot ledger). Pre-create
-# the full path on the host so the tier opens on first boot.
-
 mkdir -p "$FRANK_ARCHON_STATE_DIR/tune"
 # rad-tune's kernel-selection cache (see the runbook's "Tuning levers"):
 # the engine's selector reads $RADIANCE_HOME/tune/<machine>.tune at boot;
 # $RADIANCE_HOME defaults to /opt/radiance, which lives in the image, so
 # the cache must ride a host mount or it dies with the --rm container
-# that wrote it. The dir is pre-created for the same reason as kvcache
-# (the engine's create is not recursive).
+# that wrote it. The engine's create is not recursive, so the dir is pre-created.
 
 if [ ! -e /dev/kfd ] || [ ! -d /dev/dri ]; then
     echo "ERROR: GPU device nodes absent (/dev/kfd, /dev/dri)" >&2
@@ -148,6 +140,15 @@ done
 LOG=/home/dank/logs/frank_archon.log
 mkdir -p "$(dirname "$LOG")"
 
+# Interleave is opt-in: 0 is the engine's default and passing it anyway would put
+# a flag in argv that changes nothing but the record. The sharing cap is always
+# explicit because `auto` vs `off` is the difference between decode waiting one
+# chunk and waiting the whole step.
+PREFILL_ARGS=()
+if [ "${FRANK_ARCHON_PREFILL_INTERLEAVE:-0}" -gt 0 ]; then
+    PREFILL_ARGS=(--prefill-interleave "$FRANK_ARCHON_PREFILL_INTERLEAVE")
+fi
+
 # Publisher-vetted container contract (docs/DOCKER.md, compose/common.yaml):
 # --network host (the server binds the host's addresses directly, no NAT),
 # --init (the engine releases the cards on SIGTERM), seccomp=unconfined
@@ -156,8 +157,9 @@ mkdir -p "$(dirname "$LOG")"
 # makes for host memory), memlock unbounded (the pinned ledger — legal
 # because the root unit grants LimitMEMLOCK=infinity to this dank process),
 # /dev/kfd + /dev/dri (render/video groups are moot for a root container).
-# The template rides a single-file mount; the .rad dir is ro; /data holds
-# the prefix-cache disk tier.
+# The template rides a single-file mount and the .rad dir is ro. The prefix cache
+# has no disk tier any more, so the only host state this container writes is the
+# rad-tune cache under /opt/radiance/share/radiance/tune.
 podman run -d --name "$FRANK_ARCHON_CONTAINER" \
   --network host \
   --init \
@@ -165,7 +167,6 @@ podman run -d --name "$FRANK_ARCHON_CONTAINER" \
   --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 \
   "$FRANK_ARCHON_IMAGE" \
@@ -179,15 +180,13 @@ podman run -d --name "$FRANK_ARCHON_CONTAINER" \
   --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 "$FRANK_ARCHON_PREFIX_HOST_MIB" \
-  --prefix-cache-dir /data/kvcache/frank-archon \
-  --prefix-cache-disk-mib "$FRANK_ARCHON_PREFIX_DISK_MIB" \
+  --prefix-cache-mib "$FRANK_ARCHON_PREFIX_CACHE_MIB" \
   --ngram-placement "$FRANK_ARCHON_NGRAM_PLACEMENT" \
   --num-speculative-tokens "$FRANK_ARCHON_SPEC_TOKENS" \
   --max-num-batched-tokens "$FRANK_ARCHON_MAX_BATCHED_TOKENS" \
+  --busy-prefill-chunk "$FRANK_ARCHON_BUSY_PREFILL_CHUNK" \
+  "${PREFILL_ARGS[@]}" \
   ${FRANK_ARCHON_EXTRA_ARGS:+$FRANK_ARCHON_EXTRA_ARGS} \
   > "$LOG" 2>&1