To be clear, the only file in question is requirements.txt; Docker has no idea what files `pip install ...` is pulling and doesn't factor them into any kind of cache check. Beyond that, I didn't realize that timestamps were factored into the hash, or at least if they were, I would expect git or similar to set them "correctly" such that Docker does the right thing (I still think Docker's build tooling is insane, but I'm surprised that it breaks in this case)?