Use the Flow/extension cluster and flowdb.
This will make sure code is getting their database connections correctly. We hit a bug in this with T115695: Add Flow support to Nuke.
I'm going to use the same MySQL instance (for simplicity and perf), but to fully isolate it, I'll use different wgExternalServer, usernames and passwords. That's why this is blocked on T86373: MediaWiki should not connect as root database user on MediaWiki-Vagrant (so if you connect on the app code, you can't jump to the extension cluster).
- Stop supporting update.php for Flow on MediaWiki-Vagrant? You would just run it manually like we do in production.
- Keep supporting update.php, but require trivial post-DB maintenance scripts to be written when it was previously just a SQL file added in Hooks.php.