Run the suite without -v first so a passing build shows only per-package
summaries; on failure rerun with -v for full diagnostics and exit
non-zero, matching the conditional-verbose-rerun pattern in
REPO_POLICIES.md. Add -cover to the first run per the policy's Go
example; keep -race (added in #55) and the existing nix-shell CGO
fallback for hosts without pkg-config/vips.
Model: opus-4-8