Is the light bleeding after the cessation of menstruation and the sighting of the white discharge considered menses or istihadah, and does it affect the validity of fasting in this case?

The discharge of blood after ritual purity from menstruation can be either menses (hayd) or irregular bleeding (istihada). If a woman menstruates for seven days, then becomes pure for seven days, and then blood is discharged on the fifteenth day, this blood is considered menses if it lasts for only one day, because the total period, including the previous days of purity and menstruation, does not exceed fifteen days. However, if it continues for more than one day, then it is irregular bleeding (istihada) because the total number of days will exceed fifteen days.