Fix actors added during initialization process being run twice

Also broke out the emergency halt process into a new function,
which is also now ALWAYS called 16 minutes after sigint has been
pressed, regardless if the shutdown even began in the first place.

actorset.go

@@ -35,6 +35,8 @@ type actorInfo struct {
 	// incremented automatically for each actor that is added. It is never
 	// less than one.
 	order int
+	// initial is true if this actor was added as an argument to [Run].
+	initial bool
 }
 
 // actorSetIface holds only the add/del/clear methods of actorSet.
@@ -60,23 +62,12 @@ func (sets *actorSets) All() iter.Seq[actorSetIface] {
 
 // add adds an actor under the given parent context. This is a write operation.
 func (this *actorSets) add(ctx context.Context, actor Actor) {
-	if this.inf == nil { this.inf = make(map[Actor] actorInfo)}
-	actorCtx, done := context.WithCancel(ctx)
-	this.nextOrder ++
-	info := actorInfo {
-		ctx:   actorCtx,
-		done:  done,
-		order: this.nextOrder,
-	}
-	_, isRunnable        := actor.(Runnable)
-	_, isRunShutdownable := actor.(RunShutdownable)
-	if isRunnable || isRunShutdownable {
-		info.stopped = make(chan struct { })
-	}
-	this.inf[actor] = info
-	for set := range this.All() {
-		set.add(actor)
-	}
+	this.addInternal(actorInfo { }, ctx, actor)
+}
+
+// addInitial is like add, but marks the actor as initial. This is a write operation.
+func (this *actorSets) addInitial(ctx context.Context, actor Actor) {
+	this.addInternal(actorInfo { initial: true }, ctx, actor)
 }
 
 // del removes an actor. This is a write operation.
@@ -101,6 +92,24 @@ func (this *actorSets) info(actor Actor) actorInfo {
 	return this.inf[actor]
 }
 
+func (this *actorSets) addInternal(inf actorInfo, ctx context.Context, actor Actor) {
+	if this.inf == nil { this.inf = make(map[Actor] actorInfo)}
+	actorCtx, done := context.WithCancel(ctx)
+	this.nextOrder ++
+	inf.ctx   = actorCtx
+	inf.done  = done
+	inf.order = this.nextOrder
+	_, isRunnable        := actor.(Runnable)
+	_, isRunShutdownable := actor.(RunShutdownable)
+	if isRunnable || isRunShutdownable {
+		inf.stopped = make(chan struct { })
+	}
+	this.inf[actor] = inf
+	for set := range this.All() {
+		set.add(actor)
+	}
+}
+
 // sortActors sorts actors according to the order in which they were added.
 func sortActors[T comparable] (sets *actorSets, actors []T) []T {
 	slices.SortFunc(actors, func (left, right T) int {