Lightweight metadata for one retained saved graph version.
The reference is an exact content address within the owner scope used for
the read. Owner scope is intentionally absent from this value: public graph
APIs resolve it independently, and a reference is not an authorization
credential. published_at records the first successful publication of this
distinct version; an idempotent save does not change it.
Storage backends construct this projection after validating their own rows.
Summary
Types
@type t() :: %Docket.GraphVersion{ published_at: DateTime.t(), ref: Docket.GraphRef.t() }