I’d have to imagine the written/recorded guidance for law enforcement in a situation like this is to stop the threat ASAP…

You are correct.

From WaPo:

Standard law enforcement guidance since the 1999 massacre at Columbine High School in Colorado says officers should pursue shooters inside buildings without waiting for specialized backup. Since Columbine, many police departments have trained officers to go after an attacker as soon as possible, to minimize the number of teachers and children shot. Before Columbine, older guidance often emphasized waiting for specially trained officers, such as a SWAT team. The speed and willingness of officers to pursue shooters into buildings has been called into question following other attacks in recent years, including the massacre at a high school in Parkland, Fla., in 2018.

https://www.washingtonpost.com/nation/2022/05/27/uvalde-shooting-police-gunman-shot-olivarez/