BTP issue maint-11 - proposed resolution

["Furniss, Peter" <Peter.Furniss@choreology.com>]

Title: Message

I propose we allow repetition of CANCELLED, using solution I proposed when submitting this:

 

Add additional state z2, entered on sending CANCELLED where this currently transits to z. If an imbound message is received, transit to a new query state (y3), which is exitted by resending CANCELLED, reverting to z2. Disruption (loss of volatile information) should cause a transition to existing z. (Thus the current behaviour can be treated as a disruption I.)