Test fallback root cache reuse through ordinary builds
Keep the prerequisite regression focused on real build artifacts: generic shells must exclude cached root-dependent content, while shells with known roots retain it. Ordinary requests also verify concrete cached and uncached root values.
Remove shell-debugging configuration, forced generic-shell requests, and an artificial sibling delay. Those requests exercised fresh root-fallback fills that ordinary applications cannot request before paramMatching. Runtime fresh-fill coverage belongs with a supported API scenario rather than a test-only render override.
