Type Alias PromotionExecutor 

pub type PromotionExecutor = Arc<dyn Fn(PromotionRequest) -> Result<(), String> + Send + Sync>;

The closure that actually performs the L1 promotion. Injected at construction so this module has no compile-time dependency on BlobCache.

The wiring slice will pass a closure of the form:

let cache = self.clone();
Arc::new(move |req| cache.do_l1_promotion(req))

Aliased Type

pub struct PromotionExecutor { /* private fields */ }