Files created in the .jenga sub-directory.
val prepare : unit ‑> unitPrepares the directory for special files (mkdir -p .jenga).
Not async because we do it very early (but after discover_root).
val debug : Path.Rel.tval metrics : Path.Rel.tval server : Path.Rel.tval plugin_cache : Path.Rel.tval db : version:string ‑> Path.Rel.tval local_lock : Path.Rel.tval matches : Path.t ‑> bool