I can definitively confirm that just-in-time is about trying to optimize the amount and strategic positioning of buffer needed to support the "right amount of production" to meet anticipated and actual demand, exactly as you describe.
Now, doing that can be rather difficult in the case of black swan events. But the goal is as you describe.
"Exactly enough" means "no buffer". You are simply mislabelling inventory as buffer. What people needed was buffer beyond what is cost effective given current expectations because something unexpected happened causing improbable supply irregularities.
“Exactly enough” means nothing by itself.
“Exactly enough for X” means different things based on X.
“Exactly enough for current production” means no buffer.
“Exactly enough buffering as is cost effective given current expectations of forward conditions considering the likelihood of supply irregularities, cost of production interruption, costs of inventory, etc.” does not generally mean “no buffering” unless conditions are expected to be extremely stable, or response time to changing conditions from identification to new deliveries are near instant and there is negligible risk of that changing, or there is negligible cost (including opportunity cost) to production interruption.
If you expect some supply irregularities and you don't have enough to compensate for them, that is less than enough - a shortage. Having enough for normal operations (which includes forseeable irregularities) is no buffer. A buffer is what you have in excess of that.
No, that's a degenerate fragile microoptimization inspired by seeing the short-term cost savings of just-in-time and going all in on those savings without understanding just-in-time.
What “just-in-time” actually means is dynamically exactly enough buffering as is cost effective given current expectations of forward conditions considering the likelihood of supply irregularities, cost of production interruption, costs of inventory, etc.