Reclaim KV checkpoints the index cannot reach

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/engine.rs

@@ -26,6 +26,8 @@ use validation::{validate_dspark, validate_main};
 
 pub(crate) use validation::validate_model_artifact;
 
+#[cfg(target_os = "macos")]
+pub(crate) use kvstore::sweep_unreachable as sweep_transient_cache;
 #[cfg(target_os = "macos")]
 pub(crate) use metal::configure_sources as configure_metal_sources;