Type Alias MutationClock 

pub type MutationClock = Arc<dyn Fn() -> SystemTime + Send + Sync>;

Clock the engine reads when stamping mutation timestamps. Arc’d closure rather than a trait so a test can pin a constant with one line: engine.set_mutation_clock(Arc::new(|| some_time)).

Aliased Type

pub struct MutationClock { /* private fields */ }