Specifically on the subject of input, Jon Postel said:
TCP implementations should follow a general principle of robustness:
be conservative in what you do, be liberal in what you accept from
This principle is paraphrased and misquoted all over the place, with words like "lenient", "generous", "tolerant" in place of "liberal"[*]. All of these mean the system allows variety in what input it accepts and responds to.
However, he was mostly talking about not treating input as erroneous, and whether to return errors, refuse connections, etc, or just to work as far as possible. You're talking about not hanging. A system should generally not hang unless explicitly instructed to loop forever. So if in your case the important thing to convey is that it doesn't hang/crash, you could say the system is "robust". Or you could talk about what it isn't: "faulty", "buggy", "broken". You don't generally want to tell the outside world that your system is bug-free, because generally it isn't, but internally or when talking about someone else's system you can use that kind of language.
[*] No political statement[**] intended
[**] Maybe a little bit.
I was thinking of "forgiving".. It's the first word I thought of for your system.