[Klathmon]

> it should be easy to implement a switch that would turn this part of the behaviour off

I think it's one of those "easy on the surface, but surprisingly complex" problems.

When you start allowing arbitrary code execution, it's a lot of work to prevent certain "functions" (i mean that in the non-programming way).

[dspillett]

I was thinking more along the lines of turning it off at the generation side: only including anything in the persisted state that is safe.

Trying to detect the unsafe parts so they could be turned off after that point would be impossible as you suspect (the task would be constrained by the halting problem, https://en.wikipedia.org/wiki/Halting_problem).