We have user-branches opened in the repo, so we can now replicate the same workflow we had in Phabricator. This can be done manually, but there are tools which handles it pretty well, like Introduction - spr Documentation (the doc even mentions arc!).
The next step is making sure we don’t accumulate branches, which can be done through some automation (GitHub action likely) which:
- periodically delete branches not associated with an open pull-request.
- closes PR coming from such branch without any activity after some time.
And of course documenting the flow.