Close a fact: it stops being current, and stays in history.

The half of the contract that was missing. Facts could be read and written over /v1 and only closed from the dashboard, so an agent could assert what it had learned and never retract it. Everything it got wrong stayed true forever unless a model happened to notice the contradiction.

With this, an agent that knows a fact is finished says so, and nothing has to infer it. This call asks no model. Writing a fact is another matter: POST /v1/facts asks the model for the vocabulary and the contradiction check whenever a model key is configured, and that judge may close an earlier fact on its own. Only an install with no model key writes facts with no model.

at is the date it stopped being true, not the date you noticed. Reading as_of a date before it still returns the fact, which is the whole point of keeping history instead of deleting rows.

Idempotent: forgetting a fact that is already closed changes nothing and says so.