Does Teferi's Puzzle Box affect the hand you just drew during your draw step or the hand you had before?

Teferi's Puzzle Box has a triggered ability that triggers at the beginning of each player's draw step. Crucially, the draw step already includes drawing your normal card for the turn as a turn-based action (CR 504.1). The Puzzle Box's trigger goes on the stack after that draw has already occurred, meaning the card you just drew is already in your hand when the trigger resolves.

When the trigger resolves, you shuffle all cards in your hand — including the card you drew this turn — into your library, then draw that many cards. So if you had 5 cards before your draw step and drew 1, you'd have 6 cards in hand, shuffle all 6 back, and draw 6 new cards.

This works because triggered abilities that trigger 'at the beginning of the draw step' wait until the turn-based draw action is complete, then are placed on the stack (CR 603.3). They don't interrupt the draw; they follow it.

Concrete example: You start your turn with 4 cards in hand. Your draw step begins — you draw 1 card (now 5 in hand). Teferi's Puzzle Box's ability triggers, goes on the stack, and resolves: you shuffle all 5 cards into your library and draw 5 new cards. The card you drew for the turn does NOT stay; it gets shuffled back in along with everything else.

One important note: if multiple Puzzle Boxes are in play, each trigger resolves separately. After the first resolves you draw a new hand, and the second trigger then makes you shuffle and redraw that hand (CR 603.3, 800.4).