Zero data retention is the right promise about the model layer and it has become the sentence vendors say instead of answering the harder question.
The harder question is what the agents leave behind. An agent that updates a record, drafts an email, or routes an approval generates a trace of what it did and what happened next. Multiply that across every action in an org for a year and you have an observation record that no wiki, export, or data migration can reproduce, because it was earned by acting, not written by a person.
Salesforce, to its credit, told you where that record lives. Read Stokes's line about trust as a product definition rather than a reassurance and it says: the model is a commodity, the interface is optional, and the held record is the business.
If you are a buyer, ask the three questions in the FAQ above before the credits are committed. If you are a builder, decide now whether the trace belongs to your customer, because retrofitting that decision after the record exists is the one thing nobody has managed yet.