pub fn active_variant(root: &Path) -> Option<(PathBuf, String)>Expand description
This box’s active libtorch as (variant directory, variant label),
anchored on root (a project root, or the global one).
The directory rather than its lib/: a build wants LIBTORCH_PATH
(headers included) and a child process wants lib/, so one value
serves both and neither caller has to guess which it was handed.