> If you can't trust the kernel to close() then you can't trust it to fsync() or anything else either.

https://man7.org/linux/man-pages/man2/close.2.html

       A successful close does not guarantee that the data has been
       successfully saved to disk, as the kernel uses the buffer cache to
       defer writes.  Typically, filesystems do not flush buffers when a
       file is closed.  If you need to be sure that the data is
       physically stored on the underlying disk, use fsync(2).  (It will
       depend on the disk hardware at this point.)

Of course none of this matters much on an ephemeral Github Actions VM. There's no "on next boot or whatever". So this is one environment where it makes sense to bypass all this careful durability work that I'd normally be totally behind. It seems reasonable enough to say it's reached the page cache, it should continue being visible in the current boot, and tomorrow will never come.