What's your process for keeping this in sync?

[ferdinandyb]

I'm interested how you have this set up.

[leohenon]

It's automated via sync-upstream.yml. Every 6 hours it merges upstream/dev into ocv. The known conflict spots are auto-resolved as ours, any other conflict fails the run and opens an issue so I fix it manually, and git rerere remembers the resolution so repeat conflicts resolve themselves. When upstream tags a new stable release, it also auto-publishes a matching -ocv.N release, bumping the ocv version if PRs landed.

Conflicts stay rare because the vim code lives mostly in its own files.