Hi… These are many good observations—and generally are classic initial pain points with LiteFS (which, broadly speaking, seems stuck in pre-v1.0). Without claiming to address them comprehensively…
I would like to see this, as well. You can vote for it and/or chime in with your own perspective in the following docs feedback thread:
https://community.fly.io/t/blueprints-autostart-and-stop-internal-apps-resiliency-by-machine/20343
If they only require read access to the database, then they should have volumes but should not be primary-candidates.
But if your workers do need write access, then they will have to go into the same Machine as the app. (Both can’t be primary simultaneously.)
Aside: It looks like there might be some workarounds, but they are rather intrusive changes and/or not very Rails-friendly.