CARGO_TARGET_DIR=/cargo-target redirects all build output away from
the in-tree `<crate>/target/` path, so `cp $BUILD/target/release/...`
fails after a successful compile. Mirror alpha-perception-template's
correct pattern: `cp $CARGO_TARGET_DIR/release/...`.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>