Realization: #Python dependency groups (PEP 735, added in pip 25.1) can be used for optional 'narrowing' of a dependency graph.

E.g. I have a project that depends on package shaky>=X.Y.Z, <X.Y+1 where we have some trust issues with the API stablity of the shaky upstream.

But X.Y.Z is the 'nominal' resolution of that requirement for release, higher versions are allowed as an "early warning system" for upstream breakage (i.e. in a nightly build)

So I could have a dependency group called release or nominal or something that further restricts the requirement to shaky==X.Y.Z

I don't think I am going to do this, but it's a neat trick.