Nest v4 Best Practice w/ RM?

So, been hacking on my new Hubitat C8 for a couple months and am finally getting around to hacking or new-ish Nest v4 Thermostat so that it "does the right thing" when we leave and return to the house

Before I get deep into this, since Google doesn't export ECO mode, I'm thinking the right approach is to treat the nest as dumb -- turn off all the auto tuning and machine learning on the thing -- and then, when leaving, save the current setpoints and modes to some hub vars and change the heat and cool setpoints to what would have been ECO temperatures (and the mode to auto?). Then on return, pop the old state. In effect, roll my own ECO mode.

Also, as a 4 decade embedded programmer, it would nice too get a clear statement on if or when RM rules are re-entered mid-flow, and if they are, how atomic private boolean set/clr really are as semaphores. Interestingly, when I look at logs, my rules seem to run to completion, though they often fire more triggers which leads to my rules to be repeated. That suggests an event queue or some serialization somewhere and not just an orgy of willy-nilly rule treads firing off at will.