Merge pull request 'fix SC2015 for CI shellcheck 0.9' (#1) from ic-builder/sc2015-v09 into main

CI red fix per the all-CI-green mandate; same pattern as the KNELCa/
KNELInventory fixes. No behavior change.
CI evidence: https://git.knownelement.com/KNEL/KNELPerf/actions
Ticket: https://projects.knownelement.com/issues/784

loop/baseline-diff.sh

@@ -17,7 +17,7 @@ join_tsv() { awk -F'\t' 'NR==FNR{a[$1]=$2;next} {print $1"\t"a[$1]"\t"$2"\t"$3}'
 # shellcheck disable=SC2034  # exit-status reserved for future strictness
 status=0
 join_tsv "$A/cpu-bench.tsv" "$B/cpu-bench.tsv" | while IFS=$'\t' read -r metric va vb unit; do
-  [ -n "$va" ] && [ -n "$vb" ] || continue
+  if [ -z "$va" ] || [ -z "$vb" ]; then continue; fi
   if [ "$va" = "$vb" ]; then
     printf 'OK    %-28s %s = %s %s\n' "$metric" "$va" "$vb" "$unit"
   elif [ "$va" = "${va#[-+0-9.]}" ] || [ "$vb" = "${vb#[-+0-9.]}" ]; then

scheduler/daynight/knelperf-daynight.sh

@@ -55,7 +55,7 @@ if [ -n "$BLOCK_DEVS" ]; then
   for dev in $BLOCK_DEVS; do
     blockdev --setra "$ra" "$dev" 2>/dev/null || log "readahead skip: $dev"
     for part in "${dev}"[0-9]*; do
-      [ -e "$part" ] && blockdev --setra "$ra" "$part" 2>/dev/null || true
+      if [ -e "$part" ]; then blockdev --setra "$ra" "$part" 2>/dev/null || true; fi
     done
   done
 fi