perf(frank-small): cap the CPU RAM cache at 2048 MiB

The build default is 8192 MiB. dankclaw is memory-tight (frank-large's
70 GiB GTT plus the rest of the stack) and Gemma4 runs fully on the 3090
(-ngl 999), so the CPU-side cache is not the hot path. Cap it at 2048 to
give back ~6 GiB of LPDDR. Gemma4 is not a DeltaNet model, so the
>12.8 GiB CACHE_RAM floor does not apply.

Wired through frank-small.env (CACHE_RAM) -> serve-frank-small.sh
(--cache-ram), with a wiring seam so the cap cannot be silently unwired.

scripts/frank-small.env

@@ -74,6 +74,12 @@ CTX_SIZE=1048576
 PARALLEL=4
 CACHE_TYPE_K=q8_0
 CACHE_TYPE_V=q8_0
+# CPU RAM cache cap in MiB (build default 8192). This host is memory-tight
+# (frank-large's 70 GiB GTT plus the rest of the stack), and Gemma4 runs
+# fully on the 3090 (-ngl 999), so the CPU-side cache is not the hot path;
+# cap it at 2048 to give back ~6 GiB of LPDDR. Gemma4 is not a DeltaNet
+# model, so the >12.8 GiB CACHE_RAM floor does not apply.
+CACHE_RAM=2048
 
 # Batch geometry: 8192 logical / 1024 physical. Measured on this card at
 # max length (254k-token prefill / 253k-ctx decode, 4 slots, q8 KV):

scripts/serve-frank-small.sh

@@ -58,6 +58,7 @@ fi
 : "${PARALLEL:=1}"
 : "${CACHE_TYPE_K:=f16}"
 : "${CACHE_TYPE_V:=f16}"
+: "${CACHE_RAM:=8192}"
 : "${BATCH_SIZE:=2048}"
 : "${UBATCH_SIZE:=512}"
 # Decode-shape knobs: the MTP drafter's per-round proposal length (build
@@ -130,6 +131,7 @@ exec "$LLAMA_BIN" \
     --poll "$POLL_LEVEL" \
     --cache-type-k "$CACHE_TYPE_K" \
     --cache-type-v "$CACHE_TYPE_V" \
+    --cache-ram "$CACHE_RAM" \
     "${SPEC_ARGS[@]}" \
     --jinja \
     --metrics \

tests/frank_small_unit.bats

@@ -45,6 +45,12 @@ ENV_LARGE="$REPO_ROOT/scripts/frank-large.env"
     grep -q -- '--metrics' "$SERVE"
 }
 
+@test "frank-small caps its CPU RAM cache below the build default" {
+    # Without the flag the 8192 MiB default returns and the env cap is a
+    # silent no-op; this memory-tight host needs the cap to hold.
+    grep -q -- '--cache-ram "$CACHE_RAM"' "$SERVE"
+}
+
 @test "frank-small drafts with the MTP sidecar chained behind ngram-mod" {
     grep -q '^SPEC_TYPE=draft-mtp,ngram-mod$' "$ENV_FILE"
     grep -q -- '--spec-type "$SPEC_TYPE"' "$SERVE"