fix(mcpapps): harden resource lifecycle, meta merging, and edge cases

- Clean up stale ui:// resources on toolset reload via RemoveResources
- Merge _meta.ui into existing tool Meta instead of skipping
- Guard ensureStructuredObject against typed nil slices
- Prevent duplicate Namespace key in tableToStructured
- Remove redundant loop variable capture (Go 1.22+ semantics)
- Use plain object instead of ES6 Map in protocol.js for consistency

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Signed-off-by: Marc Nuri <marc@marcnuri.com>

Author: manusa

pkg/mcp/mcp.go

@@ -64,13 +64,14 @@ func (c *Configuration) isToolApplicable(tool api.ServerTool) bool {
 }
 
 type Server struct {
-	mu             sync.RWMutex
-	configuration  *Configuration
-	server         *mcp.Server
-	enabledTools   []string
-	enabledPrompts []string
-	p              internalk8s.Provider
-	metrics        *metrics.Metrics // Metrics collection system
+	mu                   sync.RWMutex
+	configuration        *Configuration
+	server               *mcp.Server
+	enabledTools         []string
+	enabledPrompts       []string
+	registeredAppURIs    []string // tracked for cleanup on reload
+	p                    internalk8s.Provider
+	metrics              *metrics.Metrics // Metrics collection system
 }
 
 func NewServer(configuration Configuration, targetProvider internalk8s.Provider) (*Server, error) {
@@ -286,27 +287,46 @@ func (s *Server) registerPrompt(prompt api.ServerPrompt) error {
 // registerMCPAppResources registers per-tool viewer HTML as ui:// resources.
 // Each tool gets its own resource URI (e.g. ui://kubernetes-mcp-server/tool/pods_list)
 // so the viewer knows which tool it belongs to and can call it via serverTools.
+// Stale resources from previously enabled tools are removed.
 func (s *Server) registerMCPAppResources(toolNames []string) {
+	// Build the new URI set
+	newURIs := make(map[string]bool, len(toolNames))
 	for _, toolName := range toolNames {
-		tn := toolName // capture for closure
-		uri := mcpapps.ToolResourceURI(tn)
+		newURIs[mcpapps.ToolResourceURI(toolName)] = true
+	}
+	// Remove stale resources that are no longer needed
+	var staleURIs []string
+	for _, uri := range s.registeredAppURIs {
+		if !newURIs[uri] {
+			staleURIs = append(staleURIs, uri)
+		}
+	}
+	if len(staleURIs) > 0 {
+		s.server.RemoveResources(staleURIs...)
+	}
+	// Register new/updated resources
+	registeredURIs := make([]string, 0, len(toolNames))
+	for _, toolName := range toolNames {
+		uri := mcpapps.ToolResourceURI(toolName)
+		registeredURIs = append(registeredURIs, uri)
 		s.server.AddResource(
 			&mcp.Resource{
 				URI:      uri,
-				Name:     "Kubernetes MCP Apps Viewer: " + tn,
+				Name:     "Kubernetes MCP Apps Viewer: " + toolName,
 				MIMEType: mcpapps.ResourceMIMEType,
 			},
 			func(_ context.Context, _ *mcp.ReadResourceRequest) (*mcp.ReadResourceResult, error) {
 				return &mcp.ReadResourceResult{
 					Contents: []*mcp.ResourceContents{{
 						URI:      uri,
 						MIMEType: mcpapps.ResourceMIMEType,
-						Text:     mcpapps.ViewerHTMLForTool(tn),
+						Text:     mcpapps.ViewerHTMLForTool(toolName),
 					}},
 				}, nil
 			},
 		)
 	}
+	s.registeredAppURIs = registeredURIs
 }
 
 // metricsMiddleware returns a metrics middleware with access to the server's metrics system

pkg/mcp/text_result_test.go

@@ -58,6 +58,11 @@ func (s *TextResultSuite) TestEnsureStructuredObject() {
 		result := ensureStructuredObject("hello")
 		s.Equal("hello", result)
 	})
+	s.Run("passes nil slice through unchanged", func() {
+		var nilSlice []map[string]any
+		result := ensureStructuredObject(nilSlice)
+		s.Nil(result)
+	})
 }
 
 func (s *TextResultSuite) TestNewStructuredResult() {

pkg/mcp/tool_mutator.go

@@ -128,10 +128,16 @@ func createTargetListHandler(p targetLister, targetParameterName, defaultTarget
 
 // WithAppsMeta injects _meta.ui into every tool when MCP Apps is enabled.
 // Each tool gets a unique resource URI so the viewer knows which tool to call.
+// If a tool already has Meta with a "ui" key, it is left unchanged.
 func WithAppsMeta() ToolMutator {
 	return func(tool api.ServerTool) api.ServerTool {
+		appsMeta := mcpapps.ToolMetaForTool(tool.Tool.Name)
 		if tool.Tool.Meta == nil {
-			tool.Tool.Meta = mcpapps.ToolMetaForTool(tool.Tool.Name)
+			tool.Tool.Meta = appsMeta
+		} else if _, hasUI := tool.Tool.Meta["ui"]; !hasUI {
+			for k, v := range appsMeta {
+				tool.Tool.Meta[k] = v
+			}
 		}
 		return tool
 	}

pkg/mcpapps/viewer/protocol.js

@@ -2,7 +2,7 @@
   'use strict';
 
   var nextId = 1;
-  var pending = new Map();
+  var pending = {};
   var notificationHandlers = {};
   var requestHandlers = {};
 
@@ -17,7 +17,7 @@
     var id = nextId++;
     sendMessage({ jsonrpc: '2.0', id: id, method: method, params: params });
     return new Promise(function(resolve, reject) {
-      pending.set(id, { resolve: resolve, reject: reject });
+      pending[id] = { resolve: resolve, reject: reject };
     });
   }
 
@@ -43,9 +43,9 @@
     console.log('[mcp-protocol] <<', msg.method || ('response id=' + msg.id), JSON.stringify(msg).substring(0, 500));
 
     // Response to our request
-    if (msg.id != null && pending.has(msg.id)) {
-      var p = pending.get(msg.id);
-      pending.delete(msg.id);
+    if (msg.id != null && pending[msg.id]) {
+      var p = pending[msg.id];
+      delete pending[msg.id];
       if (msg.error) p.reject(new Error(msg.error.message));
       else p.resolve(msg.result);
       return;

pkg/output/output.go

@@ -162,11 +162,13 @@ func tableToStructured(t *metav1.Table) []map[string]any {
 				item[col.Name] = row.Cells[ci]
 			}
 		}
-		// Add namespace from the embedded object metadata if available
-		if row.Object.Object != nil {
-			if u, ok := row.Object.Object.(*unstructured.Unstructured); ok {
-				if ns := u.GetNamespace(); ns != "" {
-					item["Namespace"] = ns
+		// Add namespace from the embedded object metadata if not already present from column definitions
+		if _, hasNS := item["Namespace"]; !hasNS {
+			if row.Object.Object != nil {
+				if u, ok := row.Object.Object.(*unstructured.Unstructured); ok {
+					if ns := u.GetNamespace(); ns != "" {
+						item["Namespace"] = ns
+					}
 				}
 			}
 		}