I found this : https://blenderartists.org/t/set-objects-origin-to-world-0-0-0/442642/2 this : https://www.katsbits.com/codex/origin/ this : https://daler.github.io/blender-for-3d-printing/mesh_modeling/object-origin.html and this : https://gamedevacademy.org/how-to-import-blender-models-into-unity-your-one-stop-guide/
All of which through their blatant omission of mentioning a way to reset the origin to zero seem to confirm what I'm worried about: this may not be an option in blender.
And clicking around with the 3D cursor won't help, I need perfect 0,0,0.
What I'm going to do as a workaround is to close and reopen my project in order to generate a new 3D cursor, which by default should be a perfect 0,0,0
I really want a non-hack approach.