Joking aside I can’t ever remember seeing a bug in either bash or zsh, never seen either crash or segfault and anytime I’ve had weirdness it’s always turned out to be me missing something.
Both (along with a lot of the standard utilities) are a testament to what talented C programmers plus years of people beating on them in unintended ways can achieve in terms of reliability/stability.
I've been able to trigger a segfault in zsh with certain plugins, a directory with a lot of files/folders, and globs with a bunch of * characters.
It seems like a cheap and simple thing to offer your customers a little extra safety.
Anybody interested in starting a platform agnostic service to do this?