Thinking about it more, the kind of guarantees you want are the kind given by a VM for running untrusted binaries. The only difference is that you don't mind re

Thinking about it more, the kind of guarantees you want are the kind given by a VM for running untrusted binaries. The only difference is that you don't mind read-access to the host system. Yes, there will be certain things that involve system-calls or network activity that your previewer will not accurately show. But those cases fall far outside the goal of "live preview of text output of data processing pipelines".