pub fn add(root: &Path, url: &str) -> Result<DiscoveredPlugin, String>Expand description
Clone url into root under the plugin’s manifest id, validating the
result. Refuses non-URL sources (decision D1: local installs stay the
documented hand-copy), refuses an existing target directory by naming it,
and removes everything it staged on any failure. The plugin lands
disabled: enabling is a separate config step nothing here performs.