Review finding 2 (10.07 gate): a deliberately locked config (0444) in a
writable directory was silently overwritten — atomic replace creates a
fresh temp inode and renames over the read-only file, defeating the old
in-place Path.write_text PermissionError contract.
Probe the existing target with a non-truncating O_WRONLY open before any
replacement work and let the PermissionError propagate. The probe fstat()s
the fd it actually opened and hands that stat to the rest of the write, so
a concurrent writer replacing the inode between stat and probe refreshes
the metadata instead of failing (keeps concurrent-writer semantics).
Regression: writable parent + 0444 target now raises and keeps the
original bytes and mode.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
