When a memory stops being true

Brain's whole premise is that forgetting is a feature. A memory decays unless it's used; what matters resists, what doesn't fades. That handles the memory you stop caring about.

It does not handle the memory that was true on Monday and false on Wednesday.

"We deploy to Heroku" isn't low-salience noise that should quietly fade — it's a load-bearing fact you referenced constantly, right up until you migrated to Fly.io. Decay works on disuse. This is a different axis: disproof. A frequently-used, high-strength memory can become exactly wrong, and strength-based ranking will keep surfacing it with confidence precisely because it used to matter.

Decay is time-based; this is truth-based

The two need different mechanisms. Decay is a function of elapsed time since last access. Invalidation is an event: a new fact arrives that replaces an old one. You can't get the second from the first — a superseded fact might have been accessed yesterday and still be dead wrong today.

So Brain now records the relationship explicitly. When you store a memory that replaces an older one, you name what it supersedes:

{ "title": "Deploy target is Fly.io", "type": "decision",
  "supersedes": ["mem_20260101_heroku"], "content": "..." }

Brain stamps superseded_by on the old memory — in both its index entry and its file's frontmatter — and links the two.

Demote, don't delete

The obvious move is to delete the old fact. Brain doesn't, and the reason is the interesting part.

"Where do we deploy?" — the answer is Fly.io, and the superseded Heroku memory must never outrank it. But "didn't we used to be on Heroku?" is a real question with a real answer, and a deleted memory can't answer it. So a superseded memory is strongly demoted, not excluded: the recall engine multiplies its score down far enough that the successor always wins, but not to zero. It still surfaces when nothing else is relevant, and it carries superseded_by so the agent frames it correctly — "that was true until we moved to Fly.io" — instead of presenting a corpse as current.

It falls out of contradiction handling

You rarely have to think about supersedes by hand. When brain sleep consolidates, it already looks for memories that overlap. Now it distinguishes two cases: memories that are compatible get merged as before; memories that contradict get proposed as a supersession instead of silently averaged into mush. Brain never auto-resolves a contradiction — it surfaces the pair and lets you decide — but when you do decide, "the new one replaces the old" is now a first-class, recorded outcome rather than a delete-and-hope.

Details in the memorize command docs. It's a small addition with an outsized effect on one specific, corrosive failure: an agent that's confidently, fluently wrong because it remembers something that used to be right.