[IshKebab]

You could do (it is simple), but all the code is stored on crates.io so there's no real need.

An exception is for crates that wrap C code which might get the code from elsewhere but those are quite rare.

[cyberpunk]

And they’re immutable, forever? No one can pull a leftpad?

[cdirkx]

Yes, they are immutable. It's only possible to "yank" a specific version, which will prevent new dependencies, but it will still be available for download for existing dependencies.

https://doc.rust-lang.org/cargo/commands/cargo-yank.html

[dwattttt]

To elaborate on "prevent new dependencies", dependency resolution will never choose a yanked version. However the yanked version remains hosted.