Constant TERMINATED_STATE_KEY 

pub const TERMINATED_STATE_KEY: &'static str;

The state key raised (true) once a Resume::Terminate digression has ended the conversation. Governance is inert from then on: no postures, no admitted tools. The runtime does not hang up by itself — the application decides how a call ends — so watch this key (or FlowStack::is_terminated) and close the session. Published by the control plane at every turn boundary.