Function look_into_batch 

pub fn look_into_batch(
    rows: Vec<Entry>,
    cache: &CacheManager,
    each: impl FnMut(PathBuf, Measured),
)

Look into a batch of rows, handing each answer to each as it arrives, and remember what was learned.

What both background passes do — the one that measures rows on screen and the one that classifies them — because the difference between them is which rows they pick, not what is done to one. Runs on a worker; see look_into for why never here.

Every row is classified before any is measured. A kind costs one directory read and a count can cost sixty-four footers, so a batch that did both a row at a time kept the last row’s label waiting on every footer above it.