The cargo-target-cuda PVC persists `$BUILD` across runs. cargo build
mutates Cargo.lock, so the next run's `git checkout $SHA` fails with
"Your local changes to the following files would be overwritten by
checkout: Cargo.lock". Same pattern alpha-perception-template uses
(`git checkout --force $SHA; git clean -fd`) handles this cleanly.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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