> Cargo is a cross-platform tool, so when it ships a sandboxing solution it will need to be a cross-platform solution

This seems like an excuse, not an actual objection.

Linux can do seccomp or Landlock or gVisor or a combination. Seccomp and gVisor need no privileges. Windows has its internal weird mechanisms. Mac has sandbox-exec.

Cargo could easily pick an appropriate sandbox for each major platform and ship it by default.

> If you only care about Unix, then you can do this yourself today by building code in your sandbox of choice.

This is ridiculous. The sandbox should not have network access, but cargo needs network access to download the package in the first place.