I'd add pinning a rust toolchain version (using rust-toolchain.toml or similar) in addition to Cargo.lock

Rustc does have fairly frequent (every ~18 months of so) minor breaking changes between versions. These are often related to type inference, usually only affect a very small number of crates, and are usually mitigated by publishing patch versions of those crates that don't run into the issue. But if you have the patch version locked with a lockfile then that won't help you, and there is increased likelihood of the build failing, so it's best to lock down the rustc version too.

Luckily pinning the rustc version is very easy to do.

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On regular projects this kind of issue can usually also be fixed by upgrading to the latest rustc and running `cargo update`. But conservative embedded projects may have legitimate reasons for not wanting to upgrade rustc to the latest version, and parts of ecosystem's disregard for MSRVs means that running `cargo update` on an older rustc has a high chance of causing build breakage due to MSRV issues.