Prove retained connectors close on shutdown

scripts/test_mysql_persistent_pool_idle.sh

@@ -119,4 +119,25 @@ while (( SECONDS < deadline )); do
 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"
+retained=$(request /database.uce)
+IFS='|' read -r retained_pid retained_id retained_source <<<"$retained"
+[[ "$retained_pid" == "$first_pid" && "$retained_source" == "new" ]]
+connections=$(mariadb --batch --skip-column-names -e "SELECT COUNT(*) FROM information_schema.PROCESSLIST WHERE USER='$test_user'")
+[[ "$connections" == "1" ]] || { echo "shutdown fixture connection was not retained in the worker pool" >&2; exit 1; }
+
+journal_cursor=$(journalctl -u mariadb.service -n 0 --show-cursor --no-pager | sed -n 's/^-- cursor: //p')
+[[ -n "$journal_cursor" ]] || { echo "could not capture MariaDB journal cursor" >&2; exit 1; }
+kill -TERM "$server_pid"
+deadline=$((SECONDS + 10))
+while kill -0 "$server_pid" 2>/dev/null && (( SECONDS < deadline )); do sleep 0.05; done
+[[ ! -e "/proc/$server_pid" ]] || { echo "private UCE server did not stop cleanly" >&2; exit 1; }
+wait "$server_pid" 2>/dev/null || true
+server_pid=""
+sleep 1
+shutdown_log=$(journalctl -u mariadb.service --after-cursor "$journal_cursor" --no-pager)
+if grep -F "$test_user" <<<"$shutdown_log" | grep -Fq "Aborted connection"; then
+	echo "clean UCE shutdown aborted a retained MySQL connection" >&2
+	exit 1
+fi
+
+echo "Persistent MySQL idle eviction preserved hot reuse, retired expired connections, and closed a retained connection on clean shutdown"