feat: add mcpUI feature flag

Author: tsck

src/common/schemas.ts

@@ -1,4 +1,4 @@
-export const previewFeatureValues = ["search"] as const;
+export const previewFeatureValues = ["search", "mcpUI"] as const;
 export type PreviewFeature = (typeof previewFeatureValues)[number];
 
 export const similarityValues = ["cosine", "euclidean", "dotProduct"] as const;

src/tools/tool.ts

@@ -728,6 +728,10 @@ export abstract class ToolBase {
      * @returns The result with UIResource appended if conditions are met, otherwise unchanged
      */
     private appendUIResourceIfAvailable(result: CallToolResult): CallToolResult {
+        if (!this.isFeatureEnabled("mcpUI")) {
+            return result;
+        }
+
         const uiHtml = this.getUI();
         if (!uiHtml || !result.structuredContent) {
             return result;