Close retained connectors on worker shutdown

scripts/test_mysql_persistent_pool_idle.sh

@@ -108,4 +108,15 @@ third=$(request /database.uce)
 IFS='|' read -r third_pid third_id third_source <<<"$third"
 [[ "$third_pid" == "$first_pid" && "$third_source" == "new" && "$third_id" != "$first_id" ]]
 
+sleep 3
+plain=$(request /plain.uce)
+[[ "$plain" == "$first_pid|plain" ]]
+deadline=$((SECONDS + 5))
+while (( SECONDS < deadline )); do
+	connections=$(mariadb --batch --skip-column-names -e "SELECT COUNT(*) FROM information_schema.PROCESSLIST WHERE USER='$test_user'")
+	[[ "$connections" == "0" ]] && break
+	sleep 0.05
+done
+[[ "$connections" == "0" ]] || { echo "final pooled fixture connection remained after idle eviction" >&2; exit 1; }
+
 echo "Persistent MySQL idle eviction preserved hot reuse and retired the expired connection"