Initialiser functions in actors?

Does not answer your question, but you can simplify that code:

private func configureTextUpdateContinuation() {
   let u = AsyncStream<String>.makeStream ()
   self.textUpdates = u.stream
   self.textUpdateContinuation = u.continuation
}

Edit:
Also, instead of calling an instance method:

initialisation of those two variables can be done directly in the init:

init() {
   ...        
   let u = AsyncStream<String>.makeStream ()
   self.textUpdates = u.stream
   self.textUpdateContinuation = u.continuation
   ...