Three build cycles, three different missing modules — xformers, then torch at
install time, then transformers. The list had been trimmed against what the MAIN
venv provides, which is exactly backwards: an isolated venv starts with nothing,
so it needs the whole declared set, minus only the torch pins we choose and the
dev-only tools.

Verified in a throwaway container against the real core image before building
anything: audiocraft 1.3.0 on torch 2.5.1+cu121 with xformers 0.0.28.post3, and
MusicGen and AudioGen both import. That check takes two minutes; the image build
it replaces takes fifteen, which is why the last three rounds were so expensive.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0182DhR1eFNPQyGmDrpHbedY