Accept empty subordinate ID allocation files

infra/runner/find-free-subid-range.awk

@@ -7,7 +7,7 @@ NF != 3 || $2 !~ /^[0-9]+$/ || $3 !~ /^[0-9]+$/ || $3 < 1 { invalid = 1; next }
   files[FILENAME] = 1
 }
 END {
-  if (invalid || length(files) != 2) exit 2
+  if (invalid) exit 2
   for (base = 100000; base + 65535 <= 4294901760; base += 65536) {
     overlap = 0
     for (file in files)

infra/runner/test-runner-config.sh

@@ -40,6 +40,12 @@ printf 'codex:100000:65536\n' >"$fixture"
 printf 'codex:165000:1000\n' >"$fixture_g"
 range=$(awk -f infra/runner/find-free-subid-range.awk "$fixture" "$fixture_g")
 [[ $range == 231072-296607 ]]
+: >"$fixture_g"
+range=$(awk -f infra/runner/find-free-subid-range.awk "$fixture" "$fixture_g")
+[[ $range == 165536-231071 ]]
+: >"$fixture"
+range=$(awk -f infra/runner/find-free-subid-range.awk "$fixture" "$fixture_g")
+[[ $range == 100000-165535 ]]
 printf 'broken\n' >"$fixture_g"
 if awk -f infra/runner/find-free-subid-range.awk "$fixture" "$fixture_g" >/dev/null 2>&1; then
   echo 'Malformed subordinate ID allocation was accepted' >&2