What is the ruling on someone who intended to perform Umrah from the Miqat on the Day of Arafat without wearing the ihram, then intended to perform Hajj and stipulated dissolution, then returned to the Miqat and intended to perform Umrah again with the same stipulation, and entered Makkah and completed the Umrah from the Grand Mosque?

If you intended to perform Hajj and then 'Umrah, then either you are a mufrid (individual performer of Hajj, according to the Hanbali school) or a qarin (one who combines Hajj and 'Umrah, according to the view of Ibn 'Uthaymeen). In both cases, your circumambulation (tawaf) and striving (sa'i) are not for 'Umrah. Rather, the tawaf is for arrival (Qudum), and the sa'i is for Hajj. Your shaving or shortening of the hair is considered a prohibited act due to ignorance.

Since you did not stand at 'Arafat, you have missed Hajj. The general rule is that you are required to exit the state of ihram with an 'Umrah after missing Hajj, offer a sacrificial animal (hady), and make up the missed Hajj (qada'). However, if you stipulated a condition at the time of ihram, then you are not required to offer a hady or make up the Hajj.

If you have not performed a valid 'Umrah after missing Hajj, you are still in a state of ihram, and you must go to Makkah to perform the tawaf, sa'i, and shave or shorten your hair. All previous prohibitions are excused due to ignorance. However, if you contracted marriage while in a state of ihram, your marriage contract is void and must be renewed.