Keep STQ-04 fill blocks across recovery

contrib/testing/queue-failure-safety-check.sh

@@ -90,8 +90,9 @@ set -- $($as_bongo "$queue_tool" space details)
 reported_before=$4
 block=$5
 fill_blocks=$((reported_before / block + 1))
-/usr/bin/dd if=/dev/zero of="$tmpfs/fill" bs="$block" \
-    count="$fill_blocks" status=none
+exec 9>"$tmpfs/.stq04-fill"
+rm "$tmpfs/.stq04-fill"
+/usr/bin/dd if=/dev/zero bs="$block" count="$fill_blocks" status=none >&9
 $as_root /usr/bin/systemctl restart "$service"
 wait_queue
 
@@ -111,6 +112,7 @@ if ! grep -F 'Free disk space too low' "$work/full.err" >/dev/null; then
     exit 1
 fi
 $as_bongo "$queue_tool" message "$queue_id" >"$work/after-full.eml"
+exec 9>&-
 
 $as_root /usr/bin/systemctl stop "$service"
 $as_root /usr/bin/mount --bind "$blocked" "$spool"