Add --offload-mode switch for ablation (direct_read vs cached_prefill)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/bench.sh

@@ -37,6 +37,7 @@ OVERLOAD_FACTOR_ARG=""
 MAX_BATCHED_TOKENS=""
 MAX_OFFLOAD_INFLIGHT=""
 CACHE_GATE_RATIO=""
+OFFLOAD_MODE=""
 
 # Parse args
 while [[ $# -gt 0 ]]; do
@@ -53,6 +54,7 @@ while [[ $# -gt 0 ]]; do
         --max-batched-tokens) MAX_BATCHED_TOKENS="$2"; shift 2 ;;
         --max-offload-inflight) MAX_OFFLOAD_INFLIGHT="$2"; shift 2 ;;
         --cache-gate-ratio) CACHE_GATE_RATIO="$2"; shift 2 ;;
+        --offload-mode) OFFLOAD_MODE="$2"; shift 2 ;;
         *) echo "Unknown: $1"; exit 1 ;;
     esac
 done
@@ -218,6 +220,9 @@ launch_proxy() {
     if [ -n "$CACHE_GATE_RATIO" ]; then
         extra_args="$extra_args --cache-gate-ratio $CACHE_GATE_RATIO"
     fi
+    if [ -n "$OFFLOAD_MODE" ]; then
+        extra_args="$extra_args --offload-mode $OFFLOAD_MODE"
+    fi
     if [ "$MODE" = "elastic" ]; then
         local bp_list=""
         for i in $(seq 0 $((N_INSTANCES - 1))); do