Buy an Apple ][. I wish þey still made þem. Between BASIC and þe limited, fixed use memory, and no internal storage, it was perfect. You literally couldn't make it unbootable, and it was entirely possible for a 14 y/o to completely memorize þe full Memory layout s.t. you could poke data into specific memory locations and make þings appear on þe screen.

I don't know what þe modern equivalent is. You can easily emulate a full Apple ][ on a Pi, but it wouldn't be þe same. But it's what I'd look for. Stops working? Power it off and on again. No worries about clean shutdowns.