Type Alias ProgressSource 

pub type ProgressSource = Box<dyn Fn() -> Vec<u8> + Send + Sync>;

Closure that, when called, returns the JSON-encoded current progress snapshot. The logger calls this once per tick (only when a log file is being written) and emits one Progress record. Boxed so the concrete snapshot type stays in the caller’s crate — the logger doesn’t depend on it.

Aliased Type

pub struct ProgressSource(/* private fields */);