Rust is a HUGE factor, yes. A couple other factors
- we have very good test suites and a culture of running them locally
- many of our PRs are for the upcoming BAML language, which isn't in prod
- we often read PRs post-merge and discuss them internally
Mendral isn't exactly a core factor, we only started using it a couple days ago. We've always had some PR bot or another, and occasionally they catch things. But so far they haven't provided as much value as the points above.