In my experience no coding standards or cleanliness can prevent this. The only sure way is testing on commit/PR.
EDIT: A common failure mode I've noticed is that people only test the functionality they've added and not other parts of the system that may be affected.
This failure mode often comes from parts of the system being coupled when they shouldn't be, or it's not obvious that they are.
Have you ever had a change to a logging statement break cause some other code to stop functioning? I have. And I was thoroughly disappointed by the person who made a logging statement have any effect outside of logging.
Clean code needs to adhere to principles such as the Principle of Least Astonishment[0], otherwise code is bound to break when other people modify it.
[0] https://en.wikipedia.org/wiki/Principle_of_least_astonishmen...
A nicer way to say it (from pair programming ethos): If someone asks you a question to clarify some code, then it needs a comment (or a re-write/re-factor). Note that I didn't say anything about the experience level of the asker.
One more thing: I've met (multiple) people who are firmly in the "Convention over configuration" camp and the "Principle of Least Astonishment" camp and cannot understand how new joiners are continuously surprised by this or that convention.
What makes it easy to make changes, add features, find bugs, etc. is good design.
Testing can help find problems, sure, but you can't test in quality (you can only, to a degree, test in robustness).
The difference between a decent design and a mess is mostly what happens when your "simple, local fix" causes unexpected tests to fail. If your first reaction is "damn, guess we can't do that" three is a good chance you have a mess on your hands.
Clean code (yes some of this is just taste) is mostly a symptom that people have been thinking about this stuff, not a guarantee.
There is a corollary though, which is difficult. Quality of design and techniques used mostly put an upper bound on the complexity the system can have before it becomes unmanageable. If it grows long enough though, it will get there.
I think that's an issue with how people define "clean." It isn't just about surface aesthetics. Think of a cooking appliance that looks "clean" in its design, that might win a designy design award, but accumulates gunk in hard-to-reach crevices because it was only designed to look clean, not designed to be kept actually clean.