Is there an AI-first strategy for CMS design?

yes, but in my opinion it's not a new strategy.

From a site building perspective:

The problems agents bring to the table are the same problems that UGC brought to the table - new scale, untrusted users, an increased need for governance.

From a user experience perspective:

You can't ever really know if it's a human, an agent, a human driving an agent, or an agent driving a human - so stick to information architecture and accessibility best practices.

beyond that though, we're in new territory when it comes to change / scale / security / etc, so if there is a strategy it'll be out of date tomorrow.