In a trip down the rabbit hole, AGI is defined in section 62:

https://www.law.cornell.edu/uscode/text/26/62

and is a mish-mash of original definitions (educator expenses & jury duty pay remitted to the employer) and references to other sections including sections 401 pensions & 219 IRAs.  Also including sections 221 student loan interest and 222 tuition & fees (which makes including them again by reference in section 85 completely redundant.)  I didn't see 1/2 SE tax specifically but my guess would be that it's included as part of "trade and business" deductions since it's conceptually just the deductible "employer" half of FICA taxes.

I have not done an exhaustive search line-by-line and section-by-section to see what might NOT be included but most things are in there somewhere either as part of section 62 AGI or by reference from the updated section 85.

Rick