"our call stack has become a tree" This is a really useful property to have and reason about. Instead of several independent coroutines with arbitrarily overl

"our call stack has become a tree" This is a really useful property to have and reason about. Instead of several independent coroutines with arbitrarily overlapping lifetimes, we can now think of all coroutines as organized in a single hierarchy with properly nested lifetimes. The function call stack becomes a call tree - each branch is a concurrent execution.