The heartbeat opened <instance>.lock with a create-and-truncate that followed symlinks, and fell back to std::fs::write, so another account sharing SAVEFILEPATH could plant a link and have the app truncate a file of the victim's. The lock is now opened with O_NOFOLLOW|O_NONBLOCK and must be a plain file, and unlocked writes replace the file through the atomic writer. Autosave files are created 0600 regardless of umask. Lock pruning parses the folder's autosave names once instead of once per lock.
Dylan M. Taylor
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