Ah, I still reigniting this discussion again :) What about a combination of what David and Jeff say? The whole point seems to me that the salient information is not that an LLM was used (or are we going to tag Sashiko as well or any other LLM-based code review tool?), but what is was used to do. This information may be relevant for how the review is approached. The latter should perhaps only be in the cover letter and then we can drop the assisted-by tags altogether.
The question about enforcement remains.

