After some time away, I'm playing with Gnus again. In this instance,
gnus-cloud isn't working for me.

Specifically, I can add a gnus-cloud storage server (on nnimap) and
register another server (nntp) with it. ~u causes messages to be added
to Emacs-Cloud and they appear to have the right kind of content.

~d on another machine never does anything useful (e.g. mark some
articles as read) because this test:

              (if (and newer (not force-older))
                (gnus-message 3 "Skipping outdated cloud info for group %s, the info is from %s (now is %s)" group date now)

always returns true.

Looking at how `newer' is calculated, it compares the group timestamp
from the gnus-cloud message with the current time. It's not clear to me
how that test is ever going to return `nil', unless I have a version of
emacs running somewhere in the future that updates gnus-cloud.

In general I would have expected to replay any changes with a higher
sequence number, irrespective of the date of the changes. That they
happened in the past is somewhat the point, isn't it? :-)

Another problem is that after a set of Emacs-Cloud messages have been
used to replay, the emacs instance doing that replay doesn't persist the
last seen sequence value as `gnus-cloud-sequence', so the next time it
attempts to replay it will unnecessarily replay the same sequence
numbered messages again.

Attached is a suggested patch. This makes things work for me in some
limited testing.


Gnus v5.13
GNU Emacs 26.1 (build 2, x86_64-pc-linux-gnu, GTK+ Version 3.24.11)
 of 2019-09-09, modified by Debian
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