THIS CODE WAS ENTIRELY VIBE-CODED. USE AT YOUR OWN RISK!
I am not proud of this, but this was made to scratch a very old itch of mine.

mg-verify 0.1.0
vibecoded mega.nz file verifier

This tool implements MEGA's "condensed MAC" calculation[1] for files as to
verify whether it was downloaded properly or not.

It accepts a decrypted file and its respective file key, like so:

---
./mg-verify "08. Alove.mp3" lK7aaqgcVsvBA2KEiOtHGbBBvfU9qap6sRPLrdSgTY20
Computed meta-MAC : 44f2eb752813636d
Expected meta-MAC : 44f2eb752813636d

✓ MAC MATCH — file is intact.
---

You can use -v to make it verbose, which will output the AES key, nonce,
and a bunch of other things; you can also use -s to make it silent and make
it return either exit code 0 on success or exit code 1 for anything else.

[1]https://mega.nz/SecurityWhitepaper.pdf