fix(ai-mcp): keep clientOptions across the MCP Apps reconnect

`createMcpAppCallHandler` rebuilds a client per call from `getInfo()`, and that
descriptor carried only `transport` and `prefix`. So a client created with
`clientOptions` served widget tool calls through a REBUILT client that had none
— back on the SDK's AJV validator, which is the failure the option exists to
avoid, reintroduced for every MCP Apps call on an edge runtime.

`getInfo()` now reports the options the client was built with, the descriptor
carries them, and the handler forwards them. `MCPClients.getServers()` reports
them the same way, since the handler reads pools through it.

Optional on the return type rather than required: a hand-rolled `MCPClient`
would otherwise stop compiling, and it is omitted entirely when the client was
built without options, so a descriptor round-trips unchanged.

Author: L4Ph

packages/ai-mcp/src/apps/call-handler.ts

@@ -127,10 +127,12 @@ function buildRegistry(clients: McpAppClientsInput): AppRegistry {
   const add = (info: {
     transport: McpServerDescriptor['transport']
     prefix: string | undefined
+    clientOptions?: McpServerDescriptor['clientOptions']
   }) => {
     const descriptor: McpServerDescriptor = {
       transport: info.transport,
       prefix: info.prefix,
+      ...(info.clientOptions ? { clientOptions: info.clientOptions } : {}),
     }
     total += 1
     const key = info.prefix
@@ -234,6 +236,9 @@ export function createMcpAppCallHandler(opts: McpAppCallHandlerOptions) {
     const client = await createMCPClient({
       transport: descriptor.transport,
       prefix: descriptor.prefix,
+      ...(descriptor.clientOptions
+        ? { clientOptions: descriptor.clientOptions }
+        : {}),
     })
 
     try {

packages/ai-mcp/src/apps/session-store.ts

@@ -1,3 +1,4 @@
+import type { ClientOptions } from '@modelcontextprotocol/sdk/client/index.js'
 import type { TransportConfig } from '../transport'
 
 export interface McpServerDescriptor {
@@ -9,6 +10,11 @@ export interface McpServerDescriptor {
    */
   transport: TransportConfig | undefined
   prefix?: string
+  /**
+   * Options to rebuild the client with. Carried so a reconnect keeps a custom
+   * `jsonSchemaValidator` — an edge runtime cannot use the SDK's AJV default.
+   */
+  clientOptions?: ClientOptions
 }
 
 export interface McpSessionStore {

packages/ai-mcp/src/client.ts

@@ -86,6 +86,15 @@ export interface MCPClient<
   getInfo: () => {
     transport: TransportConfig | undefined
     prefix: string | undefined
+    /**
+     * The options this client was built with, so a caller that reconstructs it
+     * from this descriptor keeps them. Without it a rebuilt client silently
+     * reverts to the SDK defaults — including the AJV validator that edge
+     * runtimes cannot compile.
+     *
+     * Optional so an existing hand-rolled `MCPClient` keeps compiling.
+     */
+    clientOptions?: ClientOptions
   }
   close: () => Promise<void>
   [Symbol.asyncDispose]: () => Promise<void>
@@ -101,6 +110,10 @@ class MCPClientImpl<
   // The ORIGINAL serializable transport config (undefined for clients built
   // from a ready-made Transport instance, which is single-use / not reconnectable).
   readonly #transport: TransportConfig | undefined
+  // Retained for the same reason as #transport: the MCP Apps call handler
+  // rebuilds a client per call from getInfo(), and a rebuilt client that lost
+  // `jsonSchemaValidator` falls straight back to AJV.
+  readonly #clientOptions: ClientOptions | undefined
 
   constructor(
     prefix?: string,
@@ -111,6 +124,7 @@ class MCPClientImpl<
   ) {
     this.prefix = prefix
     this.#transport = transport
+    this.#clientOptions = clientOptions
     // `clientOptions` is spread rather than passed straight through so an
     // omitted option keeps the SDK's default. See MCPClientOptions.clientOptions
     // for why edge runtimes need `jsonSchemaValidator` in particular.
@@ -120,8 +134,13 @@ class MCPClientImpl<
   getInfo(): {
     transport: TransportConfig | undefined
     prefix: string | undefined
+    clientOptions?: ClientOptions
   } {
-    return { transport: this.#transport, prefix: this.prefix }
+    return {
+      transport: this.#transport,
+      prefix: this.prefix,
+      ...(this.#clientOptions ? { clientOptions: this.#clientOptions } : {}),
+    }
   }
 
   async connect(transport: Transport): Promise<void> {

packages/ai-mcp/src/pool.ts

@@ -7,6 +7,7 @@ import type {
   ServerDescriptor,
   ToolsOptions,
 } from './types'
+import type { ClientOptions } from '@modelcontextprotocol/sdk/client/index.js'
 import type { TransportConfig } from './transport'
 import type { ReadResourceResult } from '@modelcontextprotocol/sdk/types.js'
 
@@ -151,6 +152,7 @@ export async function createMCPClients<
       {
         transport: TransportConfig | undefined
         prefix: string | undefined
+        clientOptions?: ClientOptions
       }
     > {
       // Keyed by config key (serverId / default prefix). Read each underlying

packages/ai-mcp/tests/client.test.ts

@@ -327,4 +327,29 @@ describe('clientOptions', () => {
 
     expect(result.structuredContent).toEqual({ id: 'u-1', name: 'Ada' })
   })
+
+  it('reports clientOptions on getInfo so a rebuilt client keeps them', async () => {
+    // `createMcpAppCallHandler` reconnects per call from `getInfo()`. A
+    // descriptor that dropped `clientOptions` would hand the rebuilt client
+    // back to the SDK's AJV default — the exact failure this option exists to
+    // avoid, reintroduced for every MCP Apps widget call.
+    const { clientTransport } = await makeServerWithStructuredTool()
+    const { provider } = recordingValidator()
+    await using client = await createMCPClient({
+      transport: clientTransport,
+      prefix: 'weather',
+      clientOptions: { jsonSchemaValidator: provider },
+    })
+
+    expect(client.getInfo().clientOptions).toEqual({
+      jsonSchemaValidator: provider,
+    })
+  })
+
+  it('omits clientOptions from getInfo when none were given', async () => {
+    const { clientTransport } = await makeServerWithStructuredTool()
+    await using client = await createMCPClientFromTransport(clientTransport)
+
+    expect(client.getInfo().clientOptions).toBeUndefined()
+  })
 })