Thank you! IIUC correctly, the TLDR of that is:

    An extension to C++ that adds (pretty much) a type system on top of C++ to enable static analysis and prevention of race conditions. Widely used at Google.

Super interesting! That's exactly what Rust is doing too, except I think Rust's version (which pretty much relies on two "traits", `Send` and `Sync`) is much simpler, much more ergonomic, and much more complete.