frank-large: pin the prompt cache (16 GB) and capture the engine ledger on disk

Auto cache-sizing is OFF on this box: the boot ledger refused it at
36.9 GB (2 x full-entry) floor vs 35.7 GB free, so every deep agent
request re-prefills its whole 79-81k context (84.9-179.8 s measured on
serve_api lines, 2026-10-06) for ~500-650 new tokens per turn. Pin
HALOGEN_CACHE_MB=16384 (>= one full-slot entry at ~70 KB/token) — the
documented override; the per-store reserve re-check keeps the host safe.

Also: the serve script's 'podman run -d > LOG' captured only the
container ID — the runbook's boot-ledger grep read a one-line hex file
and the ledger existed nowhere on disk. Foreground 'podman run' makes
the ledger land in the log file as documented; exit-code and ExecStop
semantics are unchanged. Test seam updated for both.

scripts/frank-large.env

@@ -106,8 +106,22 @@ HALOGEN_DRAFTER=2
 # honor that. Do not lower the timeout alone.
 HALOGEN_MAX_TOKENS_CAP=65536
 HALOGEN_QUEUE_TIMEOUT=7200
-# Engine prompt cache: EMPTY = auto (sized from available memory at
-# startup). Pin an explicit MB only to argue with the auto figure — a
-# full-context entry is ~18 GB at 262K, so a too-small pin yields a cache
-# that reports enabled and never hits (the engine warns at startup).
-#HALOGEN_CACHE_MB=
+# Prompt cache — PINNED (2026-10-06). Auto is OFF on this box: the boot
+# ledger refused it — "serve: prompt cache OFF - 35.7 GB free after the
+# mapped checkpoint, 8.6 GB reserved for the system, which leaves less
+# than the 36.9 GB floor (2 x a 18.4 GB full-context entry). Set
+# HALOGEN_CACHE_MB to override." Auto demands TWO full-context entries;
+# the documented override is an explicit byte budget. Measured cost of
+# leaving it off: every deep agent request re-prefills its whole
+# context — 84.9-179.8 s for 46-81k prompts that grow by only ~500-650
+# tokens per turn (serve_api lines, 2026-10-06) — while the README
+# prices the cache at ~20x time-to-first-token on a warm turn.
+#
+# Sizing: an entry costs ~70 KB/token (engine figure), so ONE full-slot
+# entry (200,700 tok) is ~13.7 GB; 16384 MB holds it with margin, and
+# several ordinary 60-80k conversations under LRU-by-bytes eviction.
+# The reserve (HALOGEN_CACHE_RESERVE_MB, default 8192) is re-checked
+# against live MemAvailable on every store, so a pin cannot starve the
+# host silently. HALOGEN_CACHE_ALIGN stays at its shipped 2048 — that
+# value is what makes warm answers byte-identical to cold ones.
+HALOGEN_CACHE_MB=16384

scripts/serve-frank-large.sh

@@ -119,7 +119,7 @@ mkdir -p "$(dirname "$LOG")"
 # either. No comment lines inside the backslash
 # chain — a mid-chain # terminates the continuation (the 2026-10-05
 # exit-127 crash loop on the sibling serve script).
-podman run -d --name "$FRANK_LARGE_CONTAINER" \
+podman run --name "$FRANK_LARGE_CONTAINER" \
   --publish "$FRANK_LARGE_PUBLISH" \
   --ipc=host \
   --ulimit memlock=-1:-1 \
@@ -139,8 +139,13 @@ podman run -d --name "$FRANK_LARGE_CONTAINER" \
   "$FRANK_LARGE_IMAGE" \
   > "$LOG" 2>&1
 
-# This script's lifetime IS the container's: podman wait returns the
-# container's exit code, so a crash is a nonzero ExecStart and the unit's
-# Restart=always is real. systemd stop goes through the unit's ExecStop
-# (podman wait alone cannot stop the child).
-exec podman wait "$FRANK_LARGE_CONTAINER"
+# FOREGROUND `podman run`: the engine's stdout/stderr are this script's
+# output, so the boot ledger (kv pool, prompt cache, drafter state, any
+# clamp) lands in $LOG as documented. The previous `-d` + `exec podman
+# wait` shape captured only the container ID — the ledger existed
+# nowhere on disk and the runbook's post-deploy grep read a one-line
+# hex file (found 2026-10-06 while tuning). podman run returns the
+# container's exit code, so a crash is a nonzero ExecStart and the
+# unit's Restart=always stays real; systemd stop goes through the
+# unit's ExecStop and the run client forwards SIGTERM to the engine,
+# which drains on it.

tests/frank_large_unit.bats

@@ -74,6 +74,7 @@ good_env() {
         "HALOGEN_SLOT_CTX=200700"
         "HALOGEN_KV_SLOTS=1"
         "HALOGEN_DRAFTER=2"
+        "HALOGEN_CACHE_MB=16384"
         "STUB_DIGESTS=localhost/x ghcr.io/peonist-ai/halogen@sha256:cafe"
     )
 }
@@ -115,17 +116,20 @@ good_env() {
     [[ "$output" == *"no gfx1151 to serve on"* ]]
 }
 
-@test "the KV budget fits unified memory with margin" {
+@test "the KV pool plus pinned cache fit unified memory with margin" {
     # Pool arithmetic is the engine's documented product: slots x
-    # slot_ctx x 64 KiB. Against it: 33.4 GiB of mapped weights, the
-    # engine working set + auto prompt cache (~25 GiB of headroom
-    # allowed), host baseline and frank-small co-tenancy. The box has
-    # 121 GiB unified; the 2026-09-16 halogen era ran the same engine
-    # class here on a LARGER pool with less co-tenancy slack.
+    # slot_ctx x 64 KiB. The prompt cache is PINNED (HALOGEN_CACHE_MB,
+    # ~70 KB/token per entry — 16384 MB >= one full-slot entry). Against
+    # both: 33.4 GiB of mapped weights, ~20 GiB engine working set, host
+    # baseline and frank-small co-tenancy. The box has 121 GiB unified;
+    # the 2026-09-16 halogen era ran the same engine class here on a
+    # LARGER pool with less co-tenancy slack.
     ctx="$(sed -nE 's/^HALOGEN_SLOT_CTX=([0-9]+)$/\1/p' "$ENV_FILE")"
     slots="$(sed -nE 's/^HALOGEN_KV_SLOTS=([0-9]+)$/\1/p' "$ENV_FILE")"
+    cache_mb="$(sed -nE 's/^HALOGEN_CACHE_MB=([0-9]+)$/\1/p' "$ENV_FILE")"
     pool_gib=$(( slots * ctx * 65536 / 1073741824 ))
-    total_gib=$(( 34 + pool_gib + 25 + 15 ))
+    cache_gib=$(( ${cache_mb:-0} / 1024 ))
+    total_gib=$(( 34 + pool_gib + cache_gib + 20 + 15 ))
     [ "$total_gib" -le 121 ]
 }
 
@@ -192,9 +196,12 @@ $(cat "$TEST_TMP/serve.log")"
     [[ "$output" == *"--device $TEST_TMP/qwen.hgn"* ]]
     [[ "$output" == *"$TEST_TMP/tokenizer:/tokenizer:ro"* ]]
     [[ "$output" == *"ghcr.io/peonist-ai/halogen@sha256:cafe"* ]]
-    # The unit's restart policy is real because the script becomes
-    # `podman wait`: the container's exit code is the service's exit.
-    [[ "$output" == *"PODMAN wait frank-large-halogen"* ]]
+    # Foreground run, never -d: the engine ledger must land in the log
+    # file (`podman run -d` captured only the container ID and the
+    # runbook's ledger grep read a one-line hex file, found 2026-10-06).
+    ! grep -qE '(^|[[:space:]])-d([[:space:]]|$)' "$TEST_TMP/serve.log"
+    ! grep -q 'PODMAN wait' "$TEST_TMP/serve.log"
+    [[ "$output" == *"-e HALOGEN_CACHE_MB=16384"* ]]
 }
 
 @test "the shipped env pins the fleet's window and shape" {