XYZA Simulation Install Problems

I've been using CAMotics for some time to visualize and check G-Code programs. I'm now hand coding some simple programs with a fourth axis (XYZA). I've found CAMotics doesn't recognize the rotary axis and also doesn't recognize the global variables used in LinuxCNC, like #<_variable>. So, in a weak moment of delusion, I thought I could install a simulation version of LinuxCNC on my office computer to verify G-Code files. Great idea, I've now spent 2 solid days on it but I'm "almost" there.

I have a VirtualBox on my office computer for Windows/Fusion 360. I've been able to install a simulation mode LinuxCNC 2.9.4 (bookworm) on the Virtual Box. I could not find a four axis (XYZA) simulation version so I've installed this "sim.axis" XYZ version. It simulates fine for 3 axis (XYZ). I'm trying to add a fourth axis to this version. I think this can be done by modifying only the axis.ini file? But, with the mods I've done, the simulation doesn't move in the axis display and then faults with "joint 3 following error".

If anyone has insight in this area I'd sure like to find out what I'm doing wrong. Attached is the axis.ini file with mods noted. If you can offer assistance I'd be grateful. Thank you.

Your core assumption is unfortunately mistaken, it cannot be done by only modifying the INI file, coresim.hal is only 3 axis, the fourth axis will f-error as it is not receiving any feedback, this is expected behavior.
My suggested quick fix, in your INI file after

HALFILE = cooling.hal

add a connection to a local file like

HALFILE = fouth-axis.hal

then create the file next to the ini file with contents

net Apos joint.3.motor-pos-cmd => joint.3.motor-pos-fb

This will allow you to move your fourth axis, don't expect the rotation to look like what you expect I think A axis is rotation around X, so it might look unexpected depending on what your fourth axis does, but it should work.

If you are looking for a deeper sense of accomplishment, read the coresim.hal file and research and understand what it is doing, and why it is needed, that will get you much more satisfaction and future know how.