Just to add, the way I pictured this working was to set up a basic smithee, probably a three sided shed so I’d have a dark place to work (helps to gauge the temp of the metal by color). I’d get some of those gas welder’s goggles with the flip up flip down lens (or use my electronic welder’s hood) so I could safely look at the work in the firepot (solarpot?) then take it inside to quickly work on it. I’d stow the forge inside the smithee (or in an attached lean-to) when not using it. One feature that might be good would be a way to cover the lens and unclip it from the forge so it can be stored in a box or wrapped up, to reduce the risks of it starting a fire.
GraphineOS seems to set the benchmark for secure de-googled android phones and has a very short list of supported devices. I think I’d suggest starting with one of those, and once support eventually drops, if you’re comfortable with a reduced security capability, looking to lineageOS or similar. I think if Graphine supports a phone, it’s pretty much guaranteed to have support on the more general OSs.
For a while I looked at ruggedized smartphones (some with removable batteries!) that were supported by lineageOS and others. I didn’t find one I was convinced would hold up as long as I wanted, and I had security concerns so I ended up getting a decent secondhand phone with guaranteed security support for a few years and putting it in a good case.
Sometimes I check in on various raspberry pi smartphone projects. I love the idea and think it’d probably be able to last the longest (or be turned into something else after an upgrade) but I don’t think any feel reliable enough to me yet.