Mana, as always, thanks for your thoughts. The early years really do fly by, which is one of the (many) reasons I'm grateful to be a SAHM.

I'm generally of the mind that parents are facilitators between their children and the outside world, finding ways to creatively say yes. About 95% of the time we're in an environment that allows free exploration, so DS can have carte blanche. Another 4% of the time a simple redirection or gentle guidance does the trick to keep him behaving within the bounds of decorum. The other 1% of the time, I need to impose my will on him. In my mind, I'm trying to evaluate whether today's example, which I'd classify as a 4% moment, merits 1% moment intervention. I'm thinking probably not. Oh, asynchrony!
In hindsight, I believe I could have found a more creative solution that would have enabled some degree of controlled exploration before he fibbed, like holding his hand and going with him, or doing quick bursts of exploration of the open examining rooms between periods of waiting in the reception area.
I'm definitely prone to over-analysis, as you can see.

Thanks, everyone, for being such excellent parenting consiglieres.