Macbook pro 9,2 can't boot without this last file that got messed up
it is in folder
Try reinstalling your system.
That will probably work the best if you use a bootable installer, and not from your recovery system.
You won't lose any of your files and apps, but a macOS reinstall will scan the existing system files, reinstall those that are missing, or in the wrong location. Should also fix or replace any damaged files in the normal system install.
If you don't have an external, bootable installer, then you can try the recovery system installer, which should also get your system installed correctly.
Get there by restarting, while holding Command+r.
Choose Reinstall macOS from the menu screen.
Let us know how that goes.