Watches the board for a change, waiting until any cards turn face up or face down, are removed from the board, or change from one string to a different string.
a Memory Scramble board
ID of player watching the board; must be a nonempty string of alphanumeric or underscore characters
(a promise for) the updated state of the board from the perspective of playerId, in the format described in the PS4 handout
Watches the board for a change, waiting until any cards turn face up or face down, are removed from the board, or change from one string to a different string.