On Windows an in-process file digest can miss a rewrite that kept size and mtime (2026-11-03)

Index: Known gaps

Status (2026-11-03): OPEN, narrow.

What happens

extract/cache_input_digest.py reuses a memoized SHA-256 of a file while its stat signature (st_dev, st_ino, st_size, st_mtime_ns, st_ctime_ns) is unchanged. On POSIX st_ctime_ns is the inode change time, so any rewrite moves it. On Windows it is the file's creation time (CPython 3.12+ deprecates it as such), so a rewrite that restores both size and mtime leaves the whole signature unchanged.

Landed (#1908)

• The cross-process store (extract/cache_digest_store.py) is neither read nor written on Windows (_STORE_SIGNATURES_TRUSTED), so a later process never reuses a digest for different bytes. Before this, the test_an_edited_file_is_re_read_in_a_new_process[same_size_same_mtime] case failed on windows-latest.

Still open

• The in-process memo still applies on Windows. It is guarded only by the racy-mtime window (_RACY_WINDOW_NS), which does not cover a file whose old mtime is restored on purpose within the same process.

What would close it

A change time on Windows. os.stat does not expose one today (CPython plans to make st_ctime the change time on Windows in a later release); reading FILE_BASIC_INFO.ChangeTime through ctypes would be a Windows-only extraction path to maintain.