Function is_marker 

pub fn is_marker(name: &str) -> bool

A key that stands for something other than data a user could open: the receipts a job leaves behind, and the marker some tools write in place of a folder.

Narrower than crate::discover::is_bookkeeping on purpose. That one answers “does this count as data”, which decides a directory’s kind; this one answers “is there anything here to open”, which decides whether a row is shown at all. A leading _ is enough for the first and not for the second: _manifest.parquet is a real object somebody may want to look at, and the local listing has always shown its equivalent.