Spellsong + casting defensively?

[S'Daria]

If enemy success vs. your Perform check

1) enemy know you cast spell but they get no AoO

2) enemy know you cast and get AoO

... A) you must declare before Spellsong you cast spell defensively

... B) you declare after using Spellsong to cast defensively

[Archaeik]

On the surface this looks very similar to some kind of stealth check (using perform), but nothing about the feat suggests that you can forgo casting defensively.

My gut says

2) if they know you're casting they can make the attack

A) you make the decision to cast defensively at the same as the decision to use spellsong