fix: re-export EXTENSION_ID/getUiCapability; getHostContext() undefined pre-connect (v1 parity)

Author: felixweinberger

src/app.ts

@@ -172,7 +172,7 @@ export class App extends EventDispatcher<AppEventMap> {
   /** SEP-2133 extension handle for `ui/*` methods. */
   readonly ui: ExtensionHandle<McpUiAppCapabilities, McpUiHostCapabilities, ClientContext>;
 
-  private _hostContext: McpUiHostContext = {};
+  private _hostContext?: McpUiHostContext;
   private _hostInfo?: Implementation;
   private _resizeObserver?: ResizeObserver;
 

src/server/index.test.ts

@@ -7,7 +7,7 @@ import {
   getUiCapability,
   EXTENSION_ID,
 } from "./index";
-import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import type { McpServer } from "@modelcontextprotocol/server";
 
 describe("registerAppTool", () => {
   it("should pass through config to server.registerTool", () => {
@@ -31,7 +31,7 @@ describe("registerAppTool", () => {
     });
 
     registerAppTool(
-      mockServer as unknown as Pick<McpServer, "registerTool">,
+      mockServer as unknown as McpServer,
       "my-tool",
       {
         title: "My Tool",
@@ -72,7 +72,7 @@ describe("registerAppTool", () => {
       };
 
       registerAppTool(
-        mockServer as unknown as Pick<McpServer, "registerTool">,
+        mockServer as unknown as McpServer,
         "my-tool",
         {
           _meta: {
@@ -107,7 +107,7 @@ describe("registerAppTool", () => {
       };
 
       registerAppTool(
-        mockServer as unknown as Pick<McpServer, "registerTool">,
+        mockServer as unknown as McpServer,
         "my-tool",
         {
           _meta: {
@@ -142,7 +142,7 @@ describe("registerAppTool", () => {
       };
 
       registerAppTool(
-        mockServer as unknown as Pick<McpServer, "registerTool">,
+        mockServer as unknown as McpServer,
         "my-tool",
         {
           _meta: {
@@ -176,7 +176,7 @@ describe("registerAppTool", () => {
       };
 
       registerAppTool(
-        mockServer as unknown as Pick<McpServer, "registerTool">,
+        mockServer as unknown as McpServer,
         "my-tool",
         {
           _meta: {

src/server/index.ts

@@ -196,3 +196,18 @@ export function clientSupportsMcpApps(
 }
 
 export type { McpUiResourceCsp, McpUiResourceMeta, McpUiToolMeta };
+
+/** SEP-2133 extension identifier for MCP Apps. Same value as MCP_APPS_EXTENSION_ID. */
+export const EXTENSION_ID = "io.modelcontextprotocol/ui";
+
+/**
+ * Returns the MCP Apps capability blob from ClientCapabilities.extensions, or
+ * undefined if the client does not declare MCP Apps support.
+ */
+export function getUiCapability(
+  clientCapabilities: ClientCapabilities | undefined | null,
+): McpUiClientCapabilities | undefined {
+  return clientCapabilities?.extensions?.[EXTENSION_ID] as
+    | McpUiClientCapabilities
+    | undefined;
+}