Function next_batch 

pub fn next_batch(
    resolved: &ResolvedIngest,
    workspace_root: &Path,
    cache_root: &Path,
    batch_size: usize,
) -> Option<Batch>

Advance the uncovered-artifact file sample (D2) — the retained rotation over a source facet’s enumerated files, one batch_size window at a time. A thin wrapper over next_rotation_batch keyed ROTATION_UNCOVERED_FILES. None when the binding has no source files (e.g. a non-enumerable medium).