Add MCP experiment toggle for build mode (#2659)

e2e-tests/helpers/page-objects/components/Settings.ts

@@ -30,6 +30,12 @@ export class Settings {
     await this.page.getByRole("switch", { name: "Auto-fix problems" }).click();
   }
 
+  async toggleEnableMcpServersForBuildMode() {
+    await this.page
+      .getByRole("switch", { name: "Enable MCP servers for Build mode" })
+      .click();
+  }
+
   async toggleAutoUpdate() {
     await this.page.getByRole("switch", { name: "Auto-update" }).click();
   }

e2e-tests/mcp.spec.ts

@@ -6,6 +6,8 @@ import { expect } from "@playwright/test";
 testSkipIfWindows("mcp - call calculator", async ({ po }) => {
   await po.setUp();
   await po.navigation.goToSettingsTab();
+  await po.page.getByRole("button", { name: "Experiments" }).click();
+  await po.settings.toggleEnableMcpServersForBuildMode();
   await po.page.getByRole("button", { name: "Tools (MCP)" }).click();
 
   await po.page
@@ -90,6 +92,8 @@ testSkipIfWindows("mcp - call calculator via http", async ({ po }) => {
   try {
     await po.setUp();
     await po.navigation.goToSettingsTab();
+    await po.page.getByRole("button", { name: "Experiments" }).click();
+    await po.settings.toggleEnableMcpServersForBuildMode();
     await po.page.getByRole("button", { name: "Tools (MCP)" }).click();
 
     // Fill in server name

package-lock.json

 {
   "name": "dyad",
-  "version": "0.36.0",
+  "version": "0.37.0-beta.1",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "dyad",
-      "version": "0.36.0",
+      "version": "0.37.0-beta.1",
       "license": "MIT",
       "dependencies": {
         "@ai-sdk/amazon-bedrock": "^4.0.46",

src/components/ChatInputControls.tsx

@@ -16,11 +16,13 @@ export function ChatInputControls({
   const enabledMcpServersCount = servers.filter((s) => s.enabled).length;
 
   // Show MCP tools picker when:
-  // 1. Mode is "agent" (backwards compatibility) OR
-  // 2. Mode is "build" AND there are enabled MCP servers
+  // 1. The enableMcpServersForBuildMode experiment is on AND
+  // 2. Mode is "agent" (backwards compatibility) OR
+  //    mode is "build" AND there are enabled MCP servers
   const showMcpToolsPicker =
-    settings?.selectedChatMode === "agent" ||
-    (settings?.selectedChatMode === "build" && enabledMcpServersCount > 0);
+    !!settings?.enableMcpServersForBuildMode &&
+    (settings?.selectedChatMode === "agent" ||
+      (settings?.selectedChatMode === "build" && enabledMcpServersCount > 0));
 
   return (
     <div className="flex items-center">

src/ipc/handlers/chat_stream_handlers.ts

@@ -1203,11 +1203,13 @@ This conversation includes one or more image attachments. When the user uploads
         }
 
         // Use MCP agent code path if:
-        // 1. Mode is explicitly "agent" (backwards compatibility for existing settings)
-        // 2. Mode is "build" AND there are enabled MCP servers
+        // 1. The enableMcpServersForBuildMode experiment is on AND
+        // 2. Mode is explicitly "agent" (backwards compatibility for existing settings)
+        //    OR mode is "build" AND there are enabled MCP servers
         if (
-          settings.selectedChatMode === "agent" ||
-          settings.selectedChatMode === "build"
+          settings.enableMcpServersForBuildMode &&
+          (settings.selectedChatMode === "agent" ||
+            settings.selectedChatMode === "build")
         ) {
           const tools = await getMcpTools(event);
           const hasEnabledMcpServers = Object.keys(tools).length > 0;

src/lib/schemas.ts

@@ -326,6 +326,7 @@ export const UserSettingsSchema = z
     autoExpandPreviewPanel: z.boolean().optional(),
     enableChatCompletionNotifications: z.boolean().optional(),
     enableNativeGit: z.boolean().optional(),
+    enableMcpServersForBuildMode: z.boolean().optional(),
     enableAutoUpdate: z.boolean(),
     releaseChannel: ReleaseChannelSchema,
     runtimeMode2: RuntimeMode2Schema.optional(),

src/lib/settingsSearchIndex.ts

@@ -32,6 +32,7 @@ export const SETTING_IDS = {
   supabase: "setting-supabase",
   neon: "setting-neon",
   nativeGit: "setting-native-git",
+  enableMcpServersForBuildMode: "setting-enable-mcp-servers-for-build-mode",
   reset: "setting-reset",
 } as const;
 
@@ -304,6 +305,15 @@ export const SETTINGS_SEARCH_INDEX: SearchableSettingItem[] = [
     sectionLabel: "Experiments",
   },
 
+  {
+    id: SETTING_IDS.enableMcpServersForBuildMode,
+    label: "Enable MCP servers for Build mode",
+    description: "Allow MCP servers to be used when in Build mode",
+    keywords: ["mcp", "build", "agent", "tools", "experiment", "server"],
+    sectionId: SECTION_IDS.experiments,
+    sectionLabel: "Experiments",
+  },
+
   // Danger Zone
   {
     id: SETTING_IDS.reset,

src/pages/settings.tsx

@@ -194,6 +194,30 @@ export default function SettingsPage() {
                   a faster, native-Git performance experience.
                 </div>
               </div>
+              <div
+                id={SETTING_IDS.enableMcpServersForBuildMode}
+                className="space-y-1 mt-4"
+              >
+                <div className="flex items-center space-x-2">
+                  <Switch
+                    id="enable-mcp-servers-for-build-mode"
+                    aria-label="Enable MCP servers for Build mode"
+                    checked={!!settings?.enableMcpServersForBuildMode}
+                    onCheckedChange={(checked) => {
+                      updateSettings({
+                        enableMcpServersForBuildMode: checked,
+                      });
+                    }}
+                  />
+                  <Label htmlFor="enable-mcp-servers-for-build-mode">
+                    Enable MCP servers for Build mode
+                  </Label>
+                </div>
+                <div className="text-sm text-gray-500 dark:text-gray-400">
+                  Allow MCP servers to be used when in Build mode. Note: MCP
+                  servers are always enabled in Agent mode.
+                </div>
+              </div>
             </div>
           </div>