Manage one requested snapshot per instance. Changes are observed through the
optional native request hooks, or through data notifications on older hosts.
There is at most one active request and one latest pending refresh. Provider,
source, history or market changes and backward replay cancel obsolete work.
Synchronous style reattachment retains pending work when its selection is
unchanged. Calculation performs no requests and never prealigns cached values.
Manage one requested snapshot per instance. Changes are observed through the optional native request hooks, or through data notifications on older hosts. There is at most one active request and one latest pending refresh. Provider, source, history or market changes and backward replay cancel obsolete work. Synchronous style reattachment retains pending work when its selection is unchanged. Calculation performs no requests and never prealigns cached values.