Local subscription boundary for already-committed operational events.
Subscription is delivery-neutral: it sends an event envelope to the caller's
mailbox and never contacts a user or a channel. Proactive human delivery still
requires Spectre.Operation.Delivery authorization.
Summary
Functions
@spec subscribe( GenServer.server() | Spectre.Instance.Ref.t(), keyword() ) :: {:ok, term()} | {:error, term()}
@spec unsubscribe(GenServer.server() | Spectre.Instance.Ref.t()) :: :ok | {:error, term()}