It's effectively impossible to guarantee this when you have a file system that unifies and re-exports. Network file systems being an obvious one, but overlayfs is in a similar position.
Even if inodes still work nowadays they will eventually run into issues a few years down the line.
Then unifying file systems is not something that POSIX support and a POSIX system shouldn't do it unless it can somehow map inodes with POSIX semantics. E.g. for a network mount spanning multiple remote filesystems you could also have multiple st_dev locally.
Even if inodes still work nowadays they will eventually run into issues a few years down the line.