mcp/server.go: changed approach to handling this error

Author: KamdynS

mcp/server.go

@@ -171,6 +171,15 @@ func AddTool[In, Out any](s *Server, t *Tool, h ToolHandlerFor[In, Out]) {
 
 func addToolErr[In, Out any](s *Server, t *Tool, h ToolHandlerFor[In, Out]) (err error) {
 	defer util.Wrapf(&err, "adding tool %q", t.Name)
+	// If the exact same Tool pointer has already been registered under this name,
+	// avoid rebuilding schemas and re-registering. This prevents duplicate
+	// registration from causing errors (and unnecessary work).
+	s.mu.Lock()
+	if existing, ok := s.tools.get(t.Name); ok && existing.tool == t {
+		s.mu.Unlock()
+		return nil
+	}
+	s.mu.Unlock()
 	st, err := newServerTool(t, h)
 	if err != nil {
 		return err

mcp/tool.go

@@ -97,31 +97,11 @@ func setSchema[T any](sfield **jsonschema.Schema, rfield **jsonschema.Resolved)
 	var err error
 	if *sfield == nil {
 		*sfield, err = jsonschema.For[T](nil)
-		if err != nil {
-			return err
-		}
 	}
-	// Resolve operates with internal state and cannot be called twice on the same
-	// Schema instance. Deep-copy the schema before resolving to avoid mutating the
-	// original (which may be reused when adding the same tool again).
-	cloned, err := func(orig *jsonschema.Schema) (*jsonschema.Schema, error) {
-		if orig == nil {
-			return nil, nil
-		}
-		b, err := json.Marshal(orig)
-		if err != nil {
-			return nil, err
-		}
-		var cp jsonschema.Schema
-		if err := json.Unmarshal(b, &cp); err != nil {
-			return nil, err
-		}
-		return &cp, nil
-	}(*sfield)
 	if err != nil {
 		return err
 	}
-	*rfield, err = cloned.Resolve(&jsonschema.ResolveOptions{ValidateDefaults: true})
+	*rfield, err = (*sfield).Resolve(&jsonschema.ResolveOptions{ValidateDefaults: true})
 	return err
 }