Function register 

pub fn register(
    picker_registry: &mut PickerRegistry,
    snippet_registry: Arc<ArcSwap<SnippetRegistry>>,
)

Register this crate’s picker sources into the supplied registry. Called by the host’s App::new at boot:

lattice_snippet::picker_sources::register(&mut picker_registry, snippet_registry);

New feature crates that ship picker sources follow this pattern (see also lattice-lsp::picker_sources::register).