An assassin cannot cast FADE on anyone else.
The ARMOR functions like an oSkill - yet it’s flagged as CtC upon conditions being met.
Therefore - if you “pre-buff” with FADE - it’s the same as having x slvl FADE skill and having cast it.
Your comparison with Demon Limb(I assume) should technically work the same as the way you disagree with Treachery/Fade.
I equip DL - I cast enchant for all/self - I take DL off and I should/all should LOSE the Enchant.
No.
It’s effectively an oSkill no matter how you look at it but one requires YOU to actually cast it while the other SELF-Casts.
They’re the exact same thing with different mechanics.