I was hopeful there was a way to also select a set of guidelines from a GreasePencil object.
Or maybe there's a way that opens the instance of InstantMeshes so you can put guidelines, so it handles the steps of export and import?
Maybe even just set the symmetry axis so it gets one guideline down the middle.
[My guess is neither was not possible, or maybe grease pencil was only annotations at the time you first build this bridging addon.]
https://igl.ethz.ch/projects/sketch-retopo/
Found CLI --help
Options:
-o, --output
Well I guess there's not way currently to send guide curls from the command line?!