#74 corrupted the persistent fallback cache again despite serialising the
fetch, so the cause isn't a write race: BuildKit evicts part of that persistent
cache mount between builds (the first build after each id bump always passed,
later ones failed). Mount /usr/local/share/.cache/yarn as tmpfs so it's clean
every build and nothing can be half-evicted; the Berry cache stays persistent.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
claude
e0a4938a78