Refine backlog policy and runtime guards

Move speculative framework items into Ideas and bump rc.14

Guard tgapi API/uploader setup and nil plugin registrations

Add missing observer Event godoc

observer.go

@@ -32,6 +32,7 @@ const (
 	HandlerSceneMessageKind HandlerEventKind = "scene_message"
 )
 
+// Event is the marker interface implemented by all observer runtime events.
 type Event interface {
 	isEvent()
 }