Interesting! I'm not very knowledgeable about this topic so I'm wondering why workflows would rely on code that doesn't remove the sources of non-determinism? (runtime errors, lack of proper serialized synchronization logic etc...)?

Or is the issue that the evolution of a language might introduce additional sources of non-determinism?

So merely upgrading without checking for these wouldn't be safe if code execution depends on the behavior of a specific runtime?

(that would probably for code that never fails at runtime I assume which also seem to be a pretty stringent requirement?)

The advantage of a virtual machine would then be that the full execution trace of the instructions can be recorded and then replayed, regardless of the higher level changing semantics?)