@futzle mine too, for 10 years. now that i’ve figured it out though the solution is ridiculously simple, it was just too buried under maths jargon for me to understand.

the two lines you see in the diagram project out from the end points, and where they intersect is where the join point needs to go.

and i can calculate the angle of those lines because they’re just half way between the angle i want for each point, and the tangent angle for the join. and… done. ?! that’s it? that’s it