refactor: pass specTypeSchema() directly to ExtensionHandle (typescript-sdk#1846 StandardSchemaV1 widening)

generated/schema.ts keeps z.custom(isSpecType()) since it composes into Zod
chains; specTypeSchema() is used at the ExtensionHandle boundary where the
SDK now accepts StandardSchemaV1. app-bridge event-map params type widened
ZodType -> StandardSchemaV1. app.ts no longer imports zod.

Author: felixweinberger

package-lock.json

@@ -197,7 +197,7 @@ import { isSpecType } from "@modelcontextprotocol/client";
 import type { ${typeImports} } from "@modelcontextprotocol/client";`,
   );
 
-  // 2. Replace z.any() placeholders for external SDK types with isSpecType-backed z.custom
+  // 2. Replace z.any() placeholders for external SDK types with specTypeSchema()
   for (const schema of EXTERNAL_TYPE_SCHEMAS) {
     const typeName = schema.replace(/Schema$/, "");
     content = content.replace(

scripts/generate-schemas.ts

@@ -26,7 +26,7 @@ import {
 } from "@modelcontextprotocol/server";
 
 import { EventDispatcher } from "./events";
-import { isSpecType } from "@modelcontextprotocol/server";
+import { specTypeSchema } from "@modelcontextprotocol/server";
 import {
   LATEST_PROTOCOL_VERSION,
   McpUiAppCapabilities,
@@ -93,9 +93,7 @@ function toExtra(ctx: ServerContext): RequestHandlerExtra {
   return { signal: ctx.mcpReq.signal };
 }
 
-const LogParamsSchema = z.custom<LoggingMessageNotification["params"]>(
-  (v) => v != null && typeof v === "object",
-);
+const LogParamsSchema = specTypeSchema("LoggingMessageNotificationParams");
 
 /** Options for constructing an {@link AppBridge `AppBridge`}. */
 export interface HostOptions extends ProtocolOptions {
@@ -124,7 +122,7 @@ export type AppBridgeEventMap = {
 
 const BRIDGE_EVENT_NOTIFICATION_SCHEMAS: Record<
   keyof AppBridgeEventMap,
-  { method: string; params: z.ZodType }
+  { method: string; params: StandardSchemaV1 }
 > = {
   sizechange: {
     method: McpUiSizeChangedNotificationSchema.shape.method.value,
@@ -634,7 +632,7 @@ export class AppBridge extends EventDispatcher<AppBridgeEventMap> {
     return this.ui.sendRequest(
       "ui/call-view-tool",
       params,
-      z.custom<CallToolResult>((v) => isSpecType("CallToolResult", v)),
+      specTypeSchema("CallToolResult"),
       options,
     );
   }
@@ -648,7 +646,7 @@ export class AppBridge extends EventDispatcher<AppBridgeEventMap> {
     return this.ui.sendRequest(
       "ui/list-view-tools",
       params,
-      z.custom<ListToolsResult>((v) => isSpecType("ListToolsResult", v)),
+      specTypeSchema("ListToolsResult"),
       options,
     );
   }

src/app-bridge.ts

@@ -20,8 +20,7 @@ import {
 import { EventDispatcher } from "./events";
 export { EventDispatcher, ProtocolWithEvents } from "./events";
 import { PostMessageTransport } from "./message-transport";
-import { isSpecType } from "@modelcontextprotocol/client";
-import { z } from "zod/v4";
+import { specTypeSchema } from "@modelcontextprotocol/client";
 import {
   LATEST_PROTOCOL_VERSION,
   McpUiAppCapabilities,
@@ -226,19 +225,15 @@ export class App extends EventDispatcher<AppEventMap> {
     // Non-spec host→iframe tool surface (renamed from tools/call & tools/list).
     this.ui.setRequestHandler(
       "ui/call-view-tool",
-      z.custom<CallToolRequest["params"]>((v) =>
-        isSpecType("CallToolRequestParams", v),
-      ),
+      specTypeSchema("CallToolRequestParams"),
       async (params, ctx) => {
         if (!this._oncalltool) throw new Error("No oncalltool handler set");
         return this._oncalltool(params, toExtra(ctx));
       },
     );
     this.ui.setRequestHandler(
       "ui/list-view-tools",
-      z.custom<ListToolsRequest["params"]>((v) =>
-        v === undefined || isSpecType("PaginatedRequestParams", v),
-      ),
+      specTypeSchema("PaginatedRequestParams"),
       async (params, ctx) => {
         if (!this._onlisttools) throw new Error("No onlisttools handler set");
         return this._onlisttools(params, toExtra(ctx));
@@ -430,7 +425,7 @@ export class App extends EventDispatcher<AppEventMap> {
     return this.ui.sendRequest(
       "ui/update-model-context",
       params,
-      z.custom<Record<string, never>>((v) => isSpecType("EmptyResult", v)),
+      specTypeSchema("EmptyResult"),
       options,
     );
   }