Calling `.watch` inside a `Computed` callback

Consider the following code:

let watcherB
const state = new Signal.State(false)
const computed = new Signal.Computed(() => {
  if (state.get()) {
    watcherB.watch(computed)
    return 1
  } else {
    return 0
  }
})

computed.get()
watcherB = new Signal.subtle.Watcher(() => {
  console.log("B notified")
});
const watcherA = new Signal.subtle.Watcher(() => {
  console.log("A notified")
});
watcherA.watch(computed)
state.set(true)

During the execution of its callback, computed makes itself watched by watcherB. The semantics as they currently stand mean that both by the spec and the polyfill at f7c550b, only "A notified" is logged. This is probably right, but is also potentially quite surprising, and may be best spelled out explicitly?

I foresee browsers doing creative strategies to optimise Signal as long as the semantics are compatible with the "push-dirty pull-execute" semantics spelled out; I worry that a case like this might end up changing behaviour there unless it's more explicitly spelled out.

tc39 / proposal-signals

Calling `.watch` inside a `Computed` callback #211