Build integrity in a language I don't write

The repository has two Rust services. I have written zero lines of Rust in them and I don't claim the language — my involvement is dependency and CI hygiene, and I'd rather say that plainly than let a lockfile commit look like Rust experience on a contribution graph.

What was wrong: Cargo.lock wasn't tracked, so the services didn't build the same way twice. Tracking it and enforcing --locked in CI makes the build reproducible. Ten minutes of work, no visible result, and it stops the class of incident where CI is green and a machine somewhere isn't.