RolledBack is not an error and not an exception: a chain that reorganises is a chain behaving normally, and a subscriber that cannot express "undo everything after this point" has a bug waiting for its first fork. Providers that never signal rollbacks declare rollbackHorizon = None so the difference is visible before subscribing rather than after.
Progress signal: the chain advanced to at and nothing matched this subscription.
Progress signal: the chain advanced to at and nothing matched this subscription.
Without it, a narrowly-scoped subscription cannot distinguish "quiet chain" from "stalled connection", and has no point to checkpoint. Emitted at provider discretion — see SubscriptionOptions.idleSignals.