To what extent are my actions during Hajj valid, especially after the first and second dissolutions (at-tahallul al-asghar and al-akbar), given that I purchased a sacrificial animal certificate (ṣakk al-hadī) and its slaughter was delayed, and what consequences will I face after leaving Saudi Arabia if I have made a mistake?

Slaughtering (Nahr) has no relation to the Tahallul (coming out of Ihram). The first Tahallul occurs by performing two out of three actions: throwing (ramy), shaving or shortening the hair (halaq or taqsir), and circumambulating (tawaf). So, whoever performs two of these three has achieved the first Tahallul, even if they have not slaughtered. Sheikh Ibn Uthaymeen clarified that Tahallul does not depend on slaughtering the sacrificial animal (Hady), because slaughtering has no relation to Tahallul. It is permissible to shave before slaughtering, based on the Prophet's (peace be upon him) statement to someone who shaved before slaughtering: "Slaughter, and there is no harm." And the verse: "And do not shave your heads until the sacrificial animal reaches its place of sacrifice" [2:196] was revealed concerning the one who is prevented (from reaching the Kaaba), and "its place of sacrifice" refers to the time when the sacrificial animal becomes permissible on the day of Nahr. Therefore, if the questioner has performed two of the three mentioned actions, he has achieved Tahallul and his Hajj is valid.