The `status` part of the tasks API reflects the internal status of a
running task. In general, we do not make backwards breaking changes to
the `status` but because it is internal we reserve the right to do so. I
suspect we will very rarely excercise that right but it is important
that we have it so we're not boxed into any particular implementation
for a request.
In some sense this is policy making by documentation change. In another
it is clarification of the way we've always thought of this field.
I also reflect the documentation change into the Javadoc in a few
places. There I acknowledge Kibana's "special relationship" with
Elasticsearch. Kibana parses `_reindex`'s `status` field and, because
we're friends with those folks, we should talk to them before we make
backwards breaking changes to it. We *want* to be friends with everyone
but there is only so much time in the day and we don't *want* to make
backwards breaking fields to `status` at all anyway. So we hope that
breaking changes documentation should be enough for other folks.
Relates to #34245.
09aaed4fe4