But stable also worked this way?
So I don’t think this is a behavioural change - they’ve just renamed it to esr and that also updates you to the latest version on that branch upon a new version being published at the point you rebuild. This is entirely expected.
As always, if you really want to be super careful, at the minimum bootstrap the new version using a dual container setup or even better maintain a staging server and checkout all the updates against your plugin population before committing it to Production.
If you don’t use a staging system imho it’s almost better to drip feed latest all the way along and deal with compatibility issues on a case by case basis as a drip feed as opposed to having a large amount of breaking changes dumped into Production at once.
Otherwise a very interesting and informative post, thanks!