## ADDED Requirements

### Requirement: Deck creation and shuffling
The game engine SHALL create a standard 52-card deck and shuffle it using a random algorithm before each hand.

#### Scenario: Full 52-card deck created
- **WHEN** a new deck is initialized
- **THEN** the deck contains exactly 52 cards covering all ranks (2 through Ace) across all four suits

#### Scenario: Deck is shuffled randomly
- **WHEN** a deck is prepared for dealing
- **THEN** the card order is randomized and differs between consecutive shuffles

### Requirement: Dealing phase execution
The game engine SHALL deal 2 hole cards to each active player, then burn and deal community cards at each street (flop, turn, river).

#### Scenario: Hole cards dealt to all players
- **WHEN** a hand begins dealing
- **THEN** each active player receives exactly 2 face-down hole cards

#### Scenario: Flop deals 3 community cards
- **WHEN** the pre-flop betting round completes
- **THEN** 3 community cards are dealt face-up to the board

#### Scenario: Turn deals 1 community card
- **WHEN** the flop betting round completes
- **THEN** 1 additional community card is dealt face-up

#### Scenario: River deals final community card
- **WHEN** the turn betting round completes
- **THEN** 1 final community card is dealt face-up

### Requirement: Betting round progression
The game engine SHALL progress through four betting rounds (pre-flop, flop, turn, river) in sequence, each starting after the player left of the dealer.

#### Scenario: Pre-flop begins first
- **WHEN** hole cards are dealt
- **THEN** the pre-flop betting round starts with the player left of the dealer button

#### Scenario: Flop follows pre-flop
- **WHEN** all active players have matched bets in the pre-flop round
- **THEN** community cards (flop) are dealt and the flop betting round begins

#### Scenario: Showdown after river
- **WHEN** the river betting round completes with 2+ active players remaining
- **THEN** a showdown is triggered where remaining hole cards are revealed

### Requirement: Blind posting
The game engine SHALL enforce small blind and big blind posting before each hand, positioned left of the dealer button.

#### Scenario: Small blind posted
- **WHEN** a new hand starts
- **THEN** the player immediately left of the dealer posts the small blind amount

#### Scenario: Big blind posted
- **WHEN** a new hand starts
- **THEN** the player two seats left of the dealer posts the big blind amount (2x small blind)

### Requirement: Player action validation
The game engine SHALL validate each player action against the current game state and reject invalid actions.

#### Scenario: Fold rejected when no bet to call
- **WHEN** a player attempts to fold but no preceding bet exists in the current round
- **THEN** the action is rejected and Check is suggested instead

#### Scenario: Raise amount validated
- **WHEN** a player attempts to raise
- **THEN** the raise amount must be at least the size of the previous bet or big blind, whichever is larger

#### Scenario: All-in limited by chip count
- **WHEN** a player goes all-in with fewer chips than the call amount
- **THEN** the player's entire stack is posted and they are marked as all-in

### Requirement: Hand evaluation and winner determination
The game engine SHALL evaluate each remaining player's best 5-card hand from their 2 hole cards and 5 community cards, then award the pot to the winner.

#### Scenario: Best hand wins the pot
- **WHEN** showdown occurs with multiple active players
- **THEN** the player with the highest-ranking poker hand wins the entire pot

#### Scenario: Split pot on tie
- **WHEN** two or more players have hands of equal rank at showdown
- **THEN** the pot is divided equally among tied players

#### Scenario: Last player standing wins without showdown
- **WHEN** all opponents fold leaving one active player
- **THEN** that player wins the pot without a showdown and hole cards are not revealed

### Requirement: Pure function state transitions
The game engine SHALL represent each action as a pure function that takes the current `GameState` and returns a new immutable `GameState`.

#### Scenario: State immutability preserved
- **WHEN** an action function is called with a game state
- **THEN** the original state object is unchanged and a new state object is returned