The self-hosted runner builds on the Pi5 alongside live services; the unthrottled build saturated all cores (Go compiler + esbuild) and took the reverse-proxied sites down. Add BUILD_CPUS build-arg → GOMAXPROCS in both build stages (caps the Go compiler and Vite's esbuild) and go build -p, plus nice/ionice on the build. Slower build, responsive host. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>