I started building this at one point. Basically there's an accompanying manifest.toml that specifies permissions for the packages with their checksums, and then

I started building this at one point. Basically there's an accompanying manifest.toml that specifies permissions for the packages with their checksums, and then it can traverse the dependency graph finding each manifest.toml. It also generated a manifest.lock so if manifests changed you would know about it. Then once it built up the sandbox it would execute the build. If no dependencies require networking, for example, it gets no networking, etc. I stopped working on it because I didn't have time, and it obviously relied on everyone doing the work of writing a manifest.toml and using my tool, plus it only supported rust and crates.io TBH it seems really easy to solve this problem, it's very well worn territory - Browser extensions have been doing the same thing for decades. Similarly, why can I upload a package with a near-0 string distance to another package? That'd help a massive amount against typosquatting. No one wants to implement it who also implements package managers I guess.