That isn't what the system was notionally designed to do

Yes. The commenter is upset because a mesh network that he helped build for another purpose also provides a convenient dense network of radios that can be used to track staff, and that this is now the primary use case.

"All of that made it really easy to just stick a beacon tag inside employee badges and measure the RSSI from the mesh lightbulbs (since they already tracked that to discover who their physical neighbors were)."

I assumed the rssi thing was there from the start, apparently mistakenly.

If it's any consolation to the original engineer it feels like a non-trivial thing to add

Most nodes in a radio based system will do rssi measurements to any other nodes that they need to communicate with directly, as part of deciding appropriate tx/rx amplification levels / when nodes are unavailable / etc. These functionalities are often easy to access to enable easier debugging, so it's a relatively straightforward change to start using them to scan other things on the same protocol etc.

The original engineer states the RSSI thing from the start because it was an input to the meshing algorithm.

Using it for location of employees was the new part.

By the time they got to "just stick a beacon tag inside employee badges and measure the RSSI from the mesh lightbulbs" it's pretty clear that it's one of the features they had in mind, though. You wouldn't "just" re-issue all your employee badges and spend engineering time on integrating it like this if tracking the employees wasn't the goal.

For some additional context, the original feature genuinely was energy efficiency. <Hotel chain> was trying to get some green certifications for a flagship and went looking for partners to do the actual efficiency stuff. That company found a sub, and so on until I was contracted to do the actual firmware. Everything got done and it was installed in a test hotel in Vegas.

After that initial success, one of the intermediary contractors came up with the surveillance idea (among others) to try and find reasons for <hotel chain> to roll the system out to more facilities.