[tracnar]

You could use this funky tool from oss-rebuild which proxies registries so they return the state they were at a past date: https://github.com/google/oss-rebuild/tree/main/cmd/timewarp

[hoistbypetard]

That... looks like it would let me do this exactly the way I want to for npm and python. For my C++ stuff, it's all vendored and manual anyway.

I had not seen that tool. Thanks for pointing it out.