Immutable evidence from a duplex session's terminal path.

:status is the native child exit code or signal, even when cleanup was unconfirmed. It is nil if no EXIT frame arrived. :confirmation is one of :confirmed, :unconfirmed, :timeout, :transport_lost, or :not_started. :scope is :process_group, :active_cgroup, or :unknown; it describes the mechanism the shim reported, not proof that an escaped descendant outside that mechanism was confined. :output is :complete, :truncated, :unknown, or a typed limit tuple such as {:limit, :line, :stdout, 65536}. Cleanup confirmation and output completeness are independent observations.