Ten hand-rolled "write a token file safely" routines each carried a
different subset of {0600-on-create, fsync, atomic_replace, parent-0700
guard, BaseException cleanup}. Two of them (iron_proxy state files,
the exchanged-JWT store) still opened the temp file at process umask
and chmod'ed afterwards - the exact TOCTOU window the others document
as fixed. None of the bare-os.replace copies got atomic_replace's
Windows-contention retry or EXDEV fallback.
utils gains fsync_dir= (absorbs auth.py's dir fsync), atomic_write_bytes
(vault blob) and mode= on atomic_write_text; the ten sites become 1-3
line callers. mkstemp creates the temp file O_EXCL at 0600 regardless of
umask, so the payload is never umask-readable.
Behavior change: iron_proxy proxy.yaml/mappings.json and the exchanged-JWT
store are now 0600 from creation and fsync'd; every credential write goes
through atomic_replace (symlink-preserving, Windows retry, EXDEV copy).
auth_nous shared store now uses atomic_replace too (it forced os.replace
with no recorded reason). secret_sources cache parent-0700 goes through
the guarded secure_parent_dir instead of an unguarded chmod.
2be8e6147a