The number of coroutine invocations, and the order in which they're cleaned up, could depend on user input. The former could be unbounded.
More formally, I'm pretty sure you can write a program that always halts, but for every pair of large numbers N, K > 0, there are at least K different input values that result in (1) at least N coroutine invocations being simultaneously active, and (2) for each of those K different input values, those invocations finish in a different order.
More formally, I'm pretty sure you can write a program that always halts, but for every pair of large numbers N, K > 0, there are at least K different input values that result in (1) at least N coroutine invocations being simultaneously active, and (2) for each of those K different input values, those invocations finish in a different order.