Function resolve 

pub fn resolve(
    git: &dyn GitRunner,
    fetcher: &dyn Fetcher,
    source: &PluginSource,
    name: &str,
    cache_root: &Path,
    user_root: &Path,
    policy: RefreshPolicy,
) -> Result<Resolved, String>

Resolve source for the plugin called name.

cache_root holds git checkouts (~/.config/lattice/cache/sources/); user_root is the plugin cache (~/.config/lattice/plugins/) a Prebuilt artifact lands in.

policy decides whether an already-cloned git source is advanced from the network; it is meaningless for Local (the tree IS the source) and for Prebuilt (which re-downloads whenever the artifact is missing).

Blocking (clone / fetch / download). Run on spawn_blocking.