A much simpler solution is to use KiCommand.
Steps:
- Construct the Edge.Cut boundary with straight lines.
- Select all continuous Edge.Cut lines for which you want rounded connections.
- Enter the appropriate KiCommand command:
- 5 mm list drawings selected round refresh
See this post for sample images. The commands in that post are really old, so use the command I show here.
This will connect the lines with KiCad arcs with the given radius (5 mm) and shorten the selected lines to fit.
(Also note that list in the command given is an artifact of KiCommand. I’ll make a note to remove the need for it in a future version of KiCommand.)