After playing around with different technical solutions, I had succeeded in creating a prototype that was good enough for me to be able to quickly generate network/graph visualizations based on multiple different but connected TODO lists.
I could now create the same sort of visualizations that lead to the idea/concept of GoalCanvas back in August, but at the speed matching that of pen and paper.
After drawing up a goal canvas for my other project (replacing the one I made manually in Cytoscape in August) and GoalCanvas itself, I drew up a higher level "Succeeding as an Indiehacker" canvas. These exercises (and the resulting visualizations) where fruitful, and I got enough self-validation to make GoalCanvas into a real product, eventually.
At this point, the prototype was available on https://goalcanvas.io, but there was no landing page and no instructions, just an editor and blank half part of the screen where the visualization would show up if you new what to write in order to get one drawn up...