So on the mission REQUIEM, I found an entry log on a terminal at the start of the mission, Dr. Halsey’s log. So Halsey rants on about how cortana deleted her termination code.
If she deleted her code then why did she go through rampancy?
The termination code would be a code a human could speak to force Cortana to shut down. That’s different than Rampancy.
The theory behind the termination code is that once the AI’s “life cycle” comes to a close (7 years) it becomes enforced and shuts down the AI before it succumbs to rampancy.
So by deleting the termination code, Cortana allowed herself to remain active through Chief’s cryo sleep and unfortunately also allowing herself to go through the rampancy stage