[avmich]

> If cosmic rays flip bits in storage or on the network, that can be detected through error coding. But there's no analogy for a CPU that allows cheap online verification of its correctness.

Note that CPU can be represented as mostly a set of memory cells, so some techniques for memory correction can probably be used with CPUs as well. https://bailleux.net/pub/ob-project-gray1.pdf

[bzzzt]

Maybe not cheap, but back in the 80's there were the Tandem NonStop mainframes that used double or triple CPU's to check calculation results for correctness.