Apologies if this is too basic, but here goes:
We’re about to start using Sage/Bedrock (possibly Trellis as well, unsure yet) as the basis for multiple sites/themes. These sites share a lot of core/common functionality that we of course want to maintain in one place/repo. In normal WP development we would accomplish that with a parent theme, and I was wondering - could you please recommend your best practices for accomplishing this with Sage?
I’d recommend extracting all of your core/common/shared code into Composer packages or WordPress plugins.
So when you start a new project, you just install the packages that you need and you’re off!
You can then write updates to your packages and run a simple update command on a site to bring in the new version. This makes it a lot easier to manage inconsistencies of your common code between sites.