I'm right, of course. 😁
IRS Publication 551 showing that two separate calculations need to be made for gain or loss:
https://www.irs.gov/publications/p551#en_US_201812_publink1000257025
IRS Publication 554 showing the sale is treated as two separate sales, personal and business:
https://www.irs.gov/publications/p544#en_US_2019_publink100072282
