Function snippet_active_predicate 

pub fn snippet_active_predicate(
    session: SnippetSessionHandle,
) -> Arc<dyn Fn(BufferId) -> bool + Send + Sync> 

Predicate for the host’s generic session-backed-minor reconciler: active-snippet-mode should be active on the active buffer exactly while a snippet session is live. The host pairs this with SnippetActiveMode::mode_id() at boot and reconciles it each overlay-sync cycle — so the host’s generic sync carries no snippet_session.is_active() literal. Keeps the “when is my mode active?” policy in this crate per feedback_mode_owns_its_surface.