What is the interaction ? it seems to me that spellstrike kinda of ignores the incapacitation on this case ? it's the first time i see a incapacitation spell attack so... what happens ?
There's no special interaction, nothing about Spellstrike lets you ignore the incapacitation trait.
The incapacitation trait says you treat your check as one degree worse, so if you hit with the strike, blinding foam misses, and if you crit with the strike, blinding foam hits.