Thanks to everyone at F-Droid for your valuable work.

Follow some basic rules so as to avoid making the mess.

Only install standard packages from distro’s repository and Python’s pseudo-official PIP. For both, keep a text file with the installed package names. No compiling from source EVER. Too much hassle to maintain.

Back up config files that I changed. Not all of them.

Keep a text file to record what I did, with exact commands etc, whenever I need to go off-road. Much experience taught me that this is a chore that is very much worth the effort.

But still, the problem you point to is real. It’s the reason for immutable distros. The idea of which I find quite tempting.

Great news.

Time to roll your own with unison over SSHFS. Can confirm it works.

It’s not elegant but you can effectively preload the tiles by just swiping around the relevant zone at a bunch of zoom levels while you have a connection. The cache is not actively purged so the tiles will be available when you need them. I’ve regularly done this.