Since AoO specifies that it disrupts on a critical hit only, aND Disruptive Stance upgrades that to disrupt on a regular hit, I wouldn't expect to see a rule about all damage disrupting spells that ive missed to this point. I think that a reaction disrupting a spell needs to state that, as part of the description of the reaction.
In general only reactions (or free actions in case of the Rangers Disrupt Prey) that can disrupt manipulate actions have a chance to disrupt a spell, and only if that spell actually makes use of a manipulate action.
The trope of trying to distract/disrupt an evil spellcaster from completing a big bad spell is common in fantasy literature.
Specifically, that there is a chance of making that spellcaster lose her spell.
Now, I'm looking through the rulebook, but all I can find is the section "Disrupted and Lost Spells" on page 303. But it doesn't explain what actions (if any) that have a chance at disrupting the casting.
Question: Is there a mechanism in PF2 which details some kind of die roll to determine if a spellcasting is lost or not (outside of casting while Stupefied).
For instance, causing damage to caster to force some kind of roll or check to keep the spell.
You have an outdated mindset about disrupting. PF2 doesn't work that way. Cheers. :-)