check_cxx_source_compiles() caches MUSRVIEW_HAS_ROOT7_API under a plain variable name with no dependency tracking, so a failure recorded once (e.g. against an older ROOT built into the same build/ directory) kept being reported as missing on every later reconfigure even after ROOT was fine. Unset both cache entries before the check so it always re-runs. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>