So i was having a discussion with people and trying to explain why Crafty Cutpurse and Alliance of Arms doesn't quite work the way they want it to, but i am having trouble finding the concrete rule that there is no priority pass during a spells resolution.
In their head
1.they can flash it in after everyone pays into it to receive the tokens
or
2.they can flash in after the spell resolves but before the tokens enter.
I explained that they have to flash it in before the spell starts to resolve, thus kind of ruining the combo.
Am i wrong in thinking this is not possible or am i just bad explaining why its not?
While Alliance of Arms is resolving, no player has priority (C.R. 117.2e), so, for example, no player can cast spells (including Crafty Cutpurse) between the time players pay mana this way (if any) and the time players create the tokens called for (review C.R. 117.1a). (Note that those tokens are created while Alliance of Arms is resolving, not after it resolves [C.R. 608.2, 608.2c].) Rather, a player can "respond to" Alliance of Arms only before that spell resolves (so before players pay mana to create tokens this way) (C.R. 117.7), and after that spell is cast. See also this thread, this thread, and this thread.
Note that this answer doesn't depend on whether the Commander variant is played. The Commander variant is not synonymous with a multiplayer game; except for Commander drafts, nothing in the rules for the Commander variant under C.R. 903 precludes applying those rules to two-player games (C.R. 903.2, 903.13a).
EDIT (Feb. 21, 2021): Some rules were renumbered in the meantime. Change second paragraph.
In their head
1.they can flash it in after everyone pays into it to receive the tokens
or
2.they can flash in after the spell resolves but before the tokens enter.
I explained that they have to flash it in before the spell starts to resolve, thus kind of ruining the combo.
Am i wrong in thinking this is not possible or am i just bad explaining why its not?
Note that this answer doesn't depend on whether the Commander variant is played. The Commander variant is not synonymous with a multiplayer game; except for Commander drafts, nothing in the rules for the Commander variant under C.R. 903 precludes applying those rules to two-player games (C.R. 903.2, 903.13a).
EDIT (Feb. 21, 2021): Some rules were renumbered in the meantime. Change second paragraph.