Thanks, @Symbioquine, for the good ideas about read-only replication, and for helping me to think more clearly through the problem -which is not in fact a problem as things stand, but more of an exercise in “scenario planning” (one discipline i never took seriously until this year of extreme drought, war on the continent, spiralling energy prices, etc.)
In fact i’m very happy with Farmier hosting my system, and would never even have ventured to think about local hosting, were it not for the appeal of certain Shiny Things (e.g. Asset Link 
) that are not yet ready for co-hosting… And once embarked on that road, then Local-first seems to me the way to go with data management, simply on principle (along with Local Food, Local Money, etc.).
But, for now: i’m just happy to know such a solution exists, and is moreover so nicely documented here -so thanks for that, mate!