protofsm: add optional daemon event on init

In this commit, we add an optional daemon event that can be specified to
dispatch during init. This is useful for instances where before we
start, we want to make sure we have a registered spend/conf notification
before normal operation starts.

We also add new unit tests to cover this, and the prior spend/conf event
additions.

protofsm/state_machine.go

@@ -135,6 +135,8 @@ type StateMachine[Event any, Env Environment] struct {
 
 	stateQuery chan stateQuery[Event, Env]
 
+	initEvent fn.Option[DaemonEvent]
+
 	startOnce sync.Once
 	stopOnce  sync.Once
 
@@ -142,10 +144,12 @@ type StateMachine[Event any, Env Environment] struct {
 }
 
 // NewStateMachine creates a new state machine given a set of daemon adapters,
-// an initial state, and an environment.
+// an initial state, an environment, and an event to process as if emitted at
+// the onset of the state machine. Such an event can be used to set up tracking
+// state such as a txid confirmation event.
 func NewStateMachine[Event any, Env Environment](adapters DaemonAdapters,
-	initialState State[Event, Env],
-	env Env) StateMachine[Event, Env] {
+	initialState State[Event, Env], env Env,
+	initEvent fn.Option[DaemonEvent]) StateMachine[Event, Env] {
 
 	return StateMachine[Event, Env]{
 		daemon:         adapters,
@@ -154,6 +158,7 @@ func NewStateMachine[Event any, Env Environment](adapters DaemonAdapters,
 		stateQuery:     make(chan stateQuery[Event, Env]),
 		quit:           make(chan struct{}),
 		env:            env,
+		initEvent:      initEvent,
 		newStateEvents: fn.NewEventDistributor[State[Event, Env]](),
 	}
 }
@@ -443,6 +448,9 @@ func (s *StateMachine[Event, Env]) applyEvents(newEvent Event) (State[Event, Env
 			currentState = transition.NextState
 
 			// Notify our subscribers of the new state transition.
+			//
+			// TODO(roasbeef): will only give us the outer state?
+			//  * let FSMs choose which state to emit?
 			s.newStateEvents.NotifySubscribers(currentState)
 
 			return nil
@@ -464,6 +472,16 @@ func (s *StateMachine[Event, Env]) driveMachine() {
 	// TODO(roasbeef): move into env? read only to start with
 	currentState := s.currentState
 
+	// Before we start, if we have an init daemon event specified, then
+	// we'll handle that now.
+	err := fn.MapOptionZ(s.initEvent, func(event DaemonEvent) error {
+		return s.executeDaemonEvent(event)
+	})
+	if err != nil {
+		log.Errorf("unable to execute init event: %w", err)
+		return
+	}
+
 	// We just started driving the state machine, so we'll notify our
 	// subscribers of this starting state.
 	s.newStateEvents.NotifySubscribers(currentState)