fix: add elicitation forwarding helper to AppBridge

Author: Avcharov

examples/basic-host/src/implementation.ts

@@ -2,7 +2,7 @@ import { RESOURCE_MIME_TYPE, getToolUiResourceUri, type McpUiSandboxProxyReadyNo
 import { Client } from "@modelcontextprotocol/sdk/client/index.js";
 import { SSEClientTransport } from "@modelcontextprotocol/sdk/client/sse.js";
 import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js";
-import { ElicitRequestSchema, ElicitResultSchema, type CallToolResult, type Resource, type Tool } from "@modelcontextprotocol/sdk/types.js";
+import type { CallToolResult, Resource, Tool } from "@modelcontextprotocol/sdk/types.js";
 import { getTheme, onThemeChange } from "./theme";
 import { HOST_STYLE_VARIABLES } from "./host-styles";
 
@@ -45,25 +45,7 @@ export async function connectToServer(serverUrl: URL): Promise<ServerInfo> {
   const resources = new Map(resourcesList.resources.map((r) => [r.uri, r]));
   log.info("Server resources:", Array.from(resources.keys()));
 
-  // Buffer elicitation/create requests until the AppBridge is ready.
-  // The promise is reset after each setBridge() call so it works across
-  // multiple sequential tool invocations.
-  let resolveBridge!: (bridge: AppBridge) => void;
-  let bridgePromise = new Promise<AppBridge>((resolve) => { resolveBridge = resolve; });
-
-  const setBridge = (bridge: AppBridge) => {
-    resolveBridge(bridge);
-    bridgePromise = new Promise<AppBridge>((resolve) => { resolveBridge = resolve; });
-  };
-
-  client.setRequestHandler(ElicitRequestSchema, async (request, extra) => {
-    const bridge = await bridgePromise;
-    return bridge.request(
-      { method: "elicitation/create", params: request.params },
-      ElicitResultSchema,
-      { signal: extra.signal },
-    );
-  });
+  const setBridge = AppBridge.setupElicitationForwarding(client);
 
   return { name, client, tools, resources, appHtmlCache: new Map(), setBridge };
 }

src/app-bridge.ts

@@ -5,6 +5,8 @@ import {
   CallToolRequestSchema,
   CallToolResult,
   CallToolResultSchema,
+  ElicitRequestSchema,
+  ElicitResultSchema,
   EmptyResult,
   Implementation,
   ListPromptsRequest,
@@ -1548,6 +1550,45 @@ export class AppBridge extends Protocol<
 
     return super.connect(transport);
   }
+
+  /**
+   * Set up automatic forwarding of `elicitation/create` requests from the MCP
+   * server through a bridge to the app.
+   *
+   * Registers a handler on the given {@link Client} that buffers incoming
+   * elicitation requests until a bridge is available, then forwards them.
+   * The returned callback must be called with the active {@link AppBridge}
+   * once it is initialized (typically right after `ui/initialize` completes).
+   * It can be called multiple times for sequential tool invocations.
+   *
+   * @returns A `setBridge` callback to resolve the current buffered request
+   *          and prepare for the next one.
+   *
+   * @example
+   * ```ts
+   * const setBridge = AppBridge.setupElicitationForwarding(client);
+   * // ... later, after the bridge + app are initialized:
+   * setBridge(appBridge);
+   * ```
+   */
+  static setupElicitationForwarding(client: Client): (bridge: AppBridge) => void {
+    let resolveBridge!: (bridge: AppBridge) => void;
+    let bridgePromise = new Promise<AppBridge>((resolve) => { resolveBridge = resolve; });
+
+    client.setRequestHandler(ElicitRequestSchema, async (request, extra) => {
+      const bridge = await bridgePromise;
+      return bridge.request(
+        { method: "elicitation/create", params: request.params },
+        ElicitResultSchema,
+        { signal: extra.signal },
+      );
+    });
+
+    return (bridge: AppBridge) => {
+      resolveBridge(bridge);
+      bridgePromise = new Promise<AppBridge>((resolve) => { resolveBridge = resolve; });
+    };
+  }
 }
 
 function deepEqual(a: any, b: any): boolean {