Thanks! This is good clarity about the index priority PEP, and I’ll work on putting something together. It will be nice to reduce some of the complexity of the metadata work by handling this part separately.
I wasn’t clear enough in my description. The index URLs differ between variant combinations, but the filenames should also differ between index URLs. The thought was that the build tag would be used as the differentiator and would contain the variant hash or some shortened form of it, but it doesn’t matter exactly where the differentiator goes in the filename, or really even what it contains, so long as it makes distribution files uniquely named. I think it’s important to keep the requirement that filenames be unique for each distribution, for the reasons you listed, as well as confusion from having them together locally when building/uploading.
I believe that having separate index URLs for each variant will allow dependencies to differ between variants of a given package while still respecting the static metadata assumption, but that’s a can of worms that I’ll wait to open until the implementation is further along.