claude-code: drop what was removed while away, render one at a time, refuse an empty settings set

Review of the nox-mesh plugin: a watch hands over what is there, not what
went, so the view is pruned to the state's keys before it starts; the
watches and the tools render one at a time, as the home's record is read
and written whole; the register answer names how an item is offered.

modules/claude-code/cmd/claude-code/node.go

@@ -104,9 +104,15 @@ func Registered(p Paths) Servers {
 	return s
 }
 
+var renderMu sync.Mutex
+
 // RenderNow writes the managed directory from the facts, the settings, the licence held and the servers
 // registered here.
 func RenderNow(p Paths, write WriteManaged) ([]string, error) {
+	// One at a time: the watches and the tools all render, and the home's record of what was placed is
+	// read and written whole.
+	renderMu.Lock()
+	defer renderMu.Unlock()
 	var facts Facts
 	if !readJSON(p.Facts, &facts) || facts.Console == "" {
 		return nil, fmt.Errorf("the mesh has not rendered %s yet; nothing to write", p.Facts)