I imagine the SQLite eschews AI generated code, but using it for testing (vulnerability, performance, etc) would seem like an easy win.

I know their proprietary testing framework is their secret sauce so we may never know...

Richard Hipp's recent talk at Software Should Work explains that AI agents have been testing SQLite and they've gotten a deluge of new bug reports from the fuzz-like testing they can do. But they do not do this in house; hobbyists and other organizations do this in their own internal agent-driven fuzzing.