diff --git a/Dockerfile b/Dockerfile
index 7c07c594d..9290eedd1 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -120,6 +120,8 @@ RUN addgroup --system --gid 1001 nodejs && \
 # Where the database dumps go (`DB_BACKUP_DIR`). Owned by the app user, so a
 # fresh named volume mounted here starts with that owner: Docker fills an
 # empty named volume from the image directory it covers, ownership included.
+# Without a mount the directory stays in the container's layer; the app reads
+# its mount table, sees that, and keeps no dump here (dump-core.mjs).
 RUN mkdir -p /var/lib/healthlog/backups && \
     chown nextjs:nodejs /var/lib/healthlog/backups && \
     chmod 700 /var/lib/healthlog/backups
diff --git a/scripts/compose-dr-drill.sh b/scripts/compose-dr-drill.sh
index a980ecc26..18538a180 100755
--- a/scripts/compose-dr-drill.sh
+++ b/scripts/compose-dr-drill.sh
@@ -210,7 +210,10 @@ done
   fail "without the volume the run read '$RUN', not 'succeeded not_persistent uploaded'"
 LEFT=$(docker exec "$PROJECT-app" sh -c 'ls -A /var/lib/healthlog/backups')
 [ -z "$LEFT" ] || fail "a dump was left in the container's layer: $LEFT"
-docker logs "$PROJECT-app" 2>&1 | grep -q "is inside the container, not on a mounted volume" ||
+# Into a file first: `grep -q` stops reading at the match, and with pipefail
+# the SIGPIPE that leaves `docker logs` would read as a miss.
+docker logs "$PROJECT-app" >"$WORK/no-volume.log" 2>&1
+grep -q "is inside the container, not on a mounted volume" "$WORK/no-volume.log" ||
   fail "the start log does not say the dump directory is inside the container"
 echo "   $RUN, nothing in the container's layer"
 stack down -v --remove-orphans >/dev/null 2>&1