End a regime (retention, the Update shape)

The phase is over. It stopped applying; it did not stop HAVING applied — memories scoped to it stay retrievable and annotate inapplicable_ended, which is what an audit needs and what a TTL field destroys. Nothing is deleted.

Requires the coord:write scope. Accepts all three lanes: a session JWT (bounded by the caller's role on this workspace) or an il_* machine credential whose own scope set, workspace set and validity window cover it — both ceilings apply and neither can raise the other, so a credential carrying coord:write is still refused where the role does not permit it.

A credential with no scope record resolves to LEGACY_DEFAULT, which does NOT include coord:write — mint a key with it explicitly (POST /v2/workspaces/{id}/keys).