Function document_staging_name 

pub fn document_staging_name(name: &OsStr) -> OsString

What the staging file of a document named name is called: the name hidden by a dot and suffixed .staging, in the document’s own directory (crates/kernel/spec/Layout.lean §8-56).

The whole-or-nothing document writer stages here and renames over the document; the checkpoint scan refuses this name before git opens it, because the file can be renamed away between the scan’s stat and its read (storage D30). Both ask this function, so the two spellings cannot drift apart.