diff --git a/engine b/engine
index e0425e6..c6c7ce8 160000
--- a/engine
+++ b/engine
@@ -1 +1 @@
-Subproject commit e0425e6108a1d965d9826e6496445b8b31a8010a
+Subproject commit c6c7ce8640f36d9cae58d3f320b3922963c6809a
diff --git a/run-harness-bench.sh b/run-harness-bench.sh
index 93373fc..75fbfea 100755
--- a/run-harness-bench.sh
+++ b/run-harness-bench.sh
@@ -174,7 +174,7 @@ run_one() {  # <variant> <rep>
 }
 
 # ---- collect ----
-: > "$DATA"
+# append-mode: data file is NOT wiped (clear manually for a fresh campaign)
 printf 'variant\trep\tsuccess\tbuilder\tadversary\ttotal\tduration_s\tcommits\tloc\n' > "$DATA.hdr"
 for v in "${VARIANTS[@]}"; do
   for rep in $(seq 1 "$REPEATS"); do run_one "$v" "$rep"; done