Below you’ll find the developer’s answer to your and my question.
My current solution is having a text-editing tool such as Drafts in split view mode side-by-side with Agenda. I write my thoughts in Drafts and then paste those notes into Agenda. Thoughts can be about course-correction of mistakes in past Agenda notes or about new ideas for the Agenda project.
But yeah, I’d love for yet another answer to this question from the developers to your post.