Replace the block/rescue that caught any error -- including templating errors in
the debug task -- with explicit conditional cleanup gated on nvidia-smi's actual
return code. A cosmetic failure can no longer roll back a working install. rc 18
(driver/library version mismatch) now fails with guidance and leaves packages intact.
Check nvidia_verification.rc is defined instead of the var, since a skipped
task still registers a dict without rc. Fall back to nvidia_check output so
driver info shows on every successful run.