ObservedChanges.next → ObservationRegistrar.nextChange (isolated) → ObservationRegistrar.scheduleNextChange (isolated) → withUnsafeContinuation ObservedChanges.next → ObservationRegistrar.nextChange (isolated) → ObservationRegistrar.scheduleNextChange (isolated) → withUnsafeContinuation ObservedChanges は init で isolation: Isolation を受け取る。