Implemented confi snapshots

internal/datasource/synthetic/synthetic.go

@@ -263,6 +263,9 @@ func (s *Synthetic) AddSignal(def SignalDef) error {
 	if def.Name == "" {
 		return errors.New("signal name must not be empty")
 	}
+	if def.Version < 1 {
+		def.Version = 1
+	}
 
 	rg, err := compileGraph(def)
 	if err != nil {
@@ -340,6 +343,16 @@ func (s *Synthetic) UpdateSignal(def SignalDef) error {
 		s.mu.Unlock()
 		return datasource.ErrNotFound
 	}
+	// Preserve the superseded revision as a backup and bump the version.
+	oldDef := old.def
+	if oldDef.Version < 1 {
+		oldDef.Version = 1
+	}
+	if err := s.backupVersion(oldDef); err != nil {
+		s.mu.Unlock()
+		return fmt.Errorf("back up revision: %w", err)
+	}
+	def.Version = oldDef.Version + 1
 	if old.cancel != nil {
 		old.cancel()
 	}