I think the tool would be much more useful with a whitelist. Do this only for grep, awk, sed and other similar tools.

Of course, much more thought is needed to try something like this. Somebody could as well use awk with its system command to do whatever..

Even an incomplete blacklist might be helpful, just in the interest of keeping perfect from being the enemy of good.

Author here: I hope something like that (syscall/capabilities limits) could work. If it is possible, it would just mostly solve the problem, I believe. I'm kinda starting to realize, that probably any command modifying some external state is potentially somewhat risky already, by potentially spinning some exponential feedback loop. (One person on lobste.rs mentioned that foo.bak.bak.bak.bak files could easily get created.) Regardless, I'm generally considering adding a shortcut/option to pause/unpause, and only execute on Ctrl-Enter when paused.

Another possibly reasonable option would be to create a (configurable) whitelist of commands that are considered safe, and keep running the pipeline automatically as long as it only contains whitelisted commands. Any time a non-whitelisted command is introduced, stop auto-running and require Ctrl+Enter or something, until the command once again consists of only whitelisted commands.

This would save you, for example, if you had a custom command called "gr" which was short for "get rid of current directory" (obviously chosen as a pathological example since it's a prefix of grep). As you type the word "grep", auto-running is paused because "g", "gr", and "gre" are not whitelisted, and then once "grep" is fully typed, it recognizes that "grep" is on the whitelist and resumes auto-running. And it never ran the dangerous "gr" command.

Or perhaps use filesystem snapshots as an undo option ... if your fs supports them, of course.

Pretty much. Is rm blacklisted? OK. How about bash -c "rm"? cp? mv? vim?

...? :D

Yah, a whitelist of commands which includes bash would probably be best. You'd be fine using it and can simply switch to chainsaw mode by adding bash to the command