The last post I wrote ended on a loose thread I have not been able to stop pulling at. Almost every memory setup I looked at had a decent answer for what to write down, and almost none of them had a real answer for what to keep. I want to sit with that second half for a while, because the more time I spend with it the more I think it is where the actual difficulty lives.
Start with the part that feels hard but mostly isn't. Noticing that an agent failed at something is close to mechanical. A tool throws an error. A test goes red. A call times out. A change gets reverted twenty minutes after it shipped. You can even catch the quiet ones, the runs where nothing errored but nobody ever confirmed the thing actually worked, by treating "ended without confirmation" as its own small failure. None of this is trivial to wire up, but it is the kind of problem that yields to rules. You can write the rules down and they hold.
So people build the detector, watch it light up, and feel like they have solved memory. They have not. They have solved the easy half and walked right up to the hard one without noticing the seam.
The hard half starts the moment you have a confirmed failure in hand and have to decide what, if anything, it means. A single failure is not one kind of thing. Sometimes it is a fluke, a flaky test or a network hiccup that will never recur and is worth nothing. Sometimes it is a real lesson, a sign that a whole approach is wrong. And sometimes it is just another face of a mistake you already recorded last week, in which case writing it down again only piles more weight onto something you already knew. The detector cannot tell these apart. It only knows that something went red. Sorting which red things deserve to become memory is judgment, and judgment does not collapse into a rule the way detection does.
