If a duskblade scores a critical hit when channeling a
spell through a melee attack, is the spell’s damage
multiplied just like the weapon’s?
The rules aren’t as clear as they could be, but the Sage is
inclined to say no. Here’s the key sentence, from the PHB II,
page 20: “If the attack is successful, the attack deals damage
normally; then the effect of the spell is resolved.”
If you score a critical hit, the attack deals the normal
(critical) damage. Then the spell resolves normally, but it’s just
a rider effect applied due to the successful attack roll—you’re
not actually using the spell in the normal manner, so it can’t
score a critical hit.
引自FAQ,关于暮刃的法术引导。我认为其他类似的能力也应该如此处理,除非有特殊说明。