Solution (source code)

= Solution

By the definition of conditional probability and <stationary distribution>[stationarity],
$$
P^*(x,y)
=\frac{\mathbb P(X_0=y,X_1=x)}{\mathbb P(X_1=x)}
=\boxed{\frac{\pi(y)P(y,x)}{\pi(x)}}.
$$
This is the transition matrix of the <time-reversed Markov chain>.