It is often desirable to retrieve commits that have been submitted for review. For example, a reviewer may wish to fetch a previously reviewed revision when subsequent changes mean that Differential's interdiff is not suitable for comparing with more recent versions, or the same or subsequent author may wish to retrieve code for an approach that was previously discarded. AIUI there is currently no way to write a tool to do this because the commits are not actually recorded. "arc patch" is useful for the most recent diff in a revision, provided the Differential summary does not differ from the commit message summary. The same tool is not suitable for older diffs. e.g. "arc patch --nobranch --diff 8476" will pull dependencies, but the dependencies are those for the revision, not for the diff. The revisions have changed since the diff was created, and the wrong diffs are pulled for the dependencies. "arc export" provides only diff output, with no commit message or dependencies. I haven't found any information for dependencies of diffs in the UI. The commit hashes *are* recorded with the commit messages, and these look like they would be useful, but only if they the commits are recorded. The most useful solution I can imagine is to push commits to a repository so that commit hashes would be consistent when fetched.

Indeed, a Mercurial store is pretty much the only way to ensure all metadata is preserved when submitting a patch up for review. Unfortunately, it is extremely complicated to have this work with security patches, which is why they were never supported in MozReview. We spent quite a while back in early 2017 trying to figure out how to make this feasible, since it was one of the best parts of MozReview, but in the end we realized it would be too large a project for our team. I'm going to WONTFIX this, but it is *possible* that some day we'll reopen it. As for now, we have our hands full with improvements to Phabricator, moz-phab, Lando, and related projects.

Btw you can manually download each patch in a series with --skip-dependencies, although I realize this would be a lot of work for a long series.