Ref T10093. Right now, Phabricator kind of guesses that arc probably pushed stuff to the staging area.
This can cause confusing/misleading errors later, if it didn't actually push.
Instead, tell Phabricator that we pushed, so we can raise more tailored messages in the web UI (e.g., make "Land Revision" say "this wasn't pushed to the staging area" instead of "whoops, error!!~").
