Yea now I remember it's Plato... Alex (beacon)'s objection to universalised deontology came, I think, from a dialogue - I can't remember or seem to find online

Yea now I remember it's Plato... Alex (beacon)'s objection to universalised deontology came, I think, from a dialogue - I can't remember or seem to find online it now, but it's probably in Republic 2? where Socrates, Cephalus, Polemarchus and Thrasymachus are getting pissed and talking about weapons and the scenario comes up "Would you give a knife back to someone who is really angry and saying they'll kill someone - or would you lie and say you lost it" or similar. And one of them says "It wouldn't be dishonourable (a real lie) to pretend in that circumstance" - as you say "feigning ignorance doesn't seem like a lie to me". So even though a Kantian lens 2000 years later, lies have a little leeway for being "economical with the truth" under difficult conditions. Kant doesn't chisel it in stone, he says make it unversalisable, in which case the firmware update just makes the new universalisable "Never tell lies unless a murderer urgently wants his knife back".