Brainstorm in upkeep + Sylvan Library in draw step

[sco0ter]

Let's assume, you have Sylvan Library in play.

In your upkeep you play Brainstorm. Draw 3 cards, put 2 other back from your hand. Crack Fetchland, shuffle.

In your drawstep, Library triggers. Draw 3 cards. Then actually you are allowed to put cards back, which you have drawn with Brainstorm.

But how does the gamestate know, which cards you have drawn with Brainstorm?

Would you just see forward while playing Brainstorm and draw these cards into a different pile / set them aside?

But what if your opponent gets a benefit then, e.g. if he knew your hand and is able to cast a "better" Cabal Therapy next turn, depending on if you put cards back from your hand or from the set aside pile.

[Lemnear]

If you read the Oracle of library you realize that you don't really put cards in your hand before the effect is finished. Aside from any trigger caused by the word "draw" Library let you basically LOOK at the Top 3, Pay 4 Life for any you want from them, put Rest back in any order.

Library is NOT a brainstorm-effect! So you can't use it to hide cards like with brainstorm

[TheInfamousBearAssassin]

If you read the Oracle of library you realize that you don't really put cards in your hand before the effect is finished. Aside from any trigger caused by the word "draw" Library let you basically LOOK at the Top 3, Pay 4 Life for any you want from them, put Rest back in any order.

Library is NOT a brainstorm-effect! So you can't use it to hide cards like with brainstorm

That's not the question.

The scenario is

a) You have a Sylvan Library in play.

b) You cast Brainstorm during your upkeep.

c) During your draw step you draw three cards, then put back two cards you drew this turn.

d) How do you know which cards are the ones you drew off of Brainstorm?

I assume you have to just keep track of it as per a normal Sylvan Library, it's not like you didn't realize you had the card in place to start with. I suppose this means letting the opponent know how many cards off of Brainstorm you put back.

[(nameless one)]

I think you'll just have to choose from the two drawn cards off of Sylvan Library and disregard whatever you've drawn from Brainstorm.

[death]

If you are knowingly going to BS + Library, you need to set aside cards you draw with BS so you can put them back with Library otherwise you won't be able to do so, like if you shuffled them in your hand.

If you need to protect cards from discard, do so by putting them on top of the library with the Brainstorm before Sylvan Library.

[cdr]

Let's assume, you have Sylvan Library in play.

In your upkeep you play Brainstorm. Draw 3 cards, put 2 other back from your hand. Crack Fetchland, shuffle.

In your drawstep, Library triggers. Draw 3 cards. Then actually you are allowed to put cards back, which you have drawn with Brainstorm.

But how does the gamestate know, which cards you have drawn with Brainstorm?

Would you just see forward while playing Brainstorm and draw these cards into a different pile / set them aside?

But what if your opponent gets a benefit then, e.g. if he knew your hand and is able to cast a "better" Cabal Therapy next turn, depending on if you put cards back from your hand or from the set aside pile.

If you don't keep the cards drawn this turn separate from the rest of your hand, they are ineligible to be put back with Sylvan Library's effect. If you don't keep the Sylvan Library cards separate, it's assumed you're choosing to pay 8 life.

[Lemnear]

Seems I misinterpreted the question, my fault. Otherwise I can't see the problem here; either you respond with brainstorm with Library on the stack or do it afterwards. Bear is right; talk with your opponent what happens each action and work through the stack.

Without communication this play is a desaster for a all 3 participants (Judge included of course)