🚀 go-pugleaf

One possibility would be:

  define your footer variables as "<$paratext[Heading1]>:<$paratext[Heading2,Heading2D]>:<$paratext[Heading3,Heading3D]"

  define Heading2D (for dummy) and Heading3D formats

  set up Heading1, Heading2, and Heading2D as run-in heads

  set Heading2D as the next paragraph style for Heading1 and Heading3D as
  the next paragraph style for Heading2 and Heading2D

Then, typing three returns after each Heading1 would create a single line consisting of three paragraphs (Heading1, Heading2D, Heading3D) that would place just the Heading1 text in the footer. Similarly, typing two returns at the end of each Heading2 would create a single line consisting of two paragraphs (Heading2 and Heading3D) that would put the text of the previous Heading1 and the text of the new Heading 2 in the footer. Heading3 text would appear only if you had entered an actual Heading3 after the most recent Heading2.