Function is_external_plugin_active 

pub fn is_external_plugin_active(
    ext: &ExternalPluginDef,
    all_deps: &[String],
    root: &Path,
    discovered_files: &[PathBuf],
) -> bool

External-plugin dry-run primitives for the CLI’s plugin-check command. Determine whether an external plugin activates against the given project.

Shared between process_external_plugins and the collision-warning helper in registry::mod so both paths agree on activation semantics.