Keep the 1.x handler registration forms as deprecated overloads (#769)

setRequestHandler(Schema, handler) and setNotificationHandler(Schema, handler) work on App and AppBridge as deprecated overloads forwarding to the 2.x method-keyed form; AppRequest, AppNotification and AppResult return as deprecated type aliases. Both removed in 3.0.

docs/migrate-to-2.md

@@ -41,8 +41,9 @@ its `Protocol` class); `@modelcontextprotocol/core` is a required peer that `cli
   Valibot. Raw zod shapes (`{ q: z.string() }`) still work with
   `registerAppTool` but are deprecated; wrap them with `z.object({...})`.
 - **`App` / `AppBridge` extend `Protocol` from `@modelcontextprotocol/client`.**
-  `ProtocolWithEvents`, `AppRequest`, `AppNotification` and `AppResult` are
+  `ProtocolWithEvents` is gone; use the SDK's `Protocol`. The `AppRequest`,
-  gone; use the SDK's `Protocol`, `Request`, `Notification` and `Result`.
+  `AppNotification` and `AppResult` unions are kept as deprecated type
+  aliases (nothing in 2.x consumes them) and will be removed in 3.0.
 - **Handler context.** Custom handlers receive the SDK 2.x context:
   `extra.signal` → `extra.mcpReq.signal`, `extra.requestId` →
   `extra.mcpReq.id`.
@@ -51,7 +52,11 @@ its `Protocol` class); `@modelcontextprotocol/core` is a required peer that `cli
   `app.setRequestHandler("some/method", { params: SomeParamsSchema }, (params, ctx) => …)`
   for custom methods (the handler receives the parsed params); the two-argument
   `setRequestHandler("tools/call", handler)` form exists only for spec-defined
-  method names.
+  method names. The 1.x `(Schema, handler)` form still works on `App` and
+  `AppBridge` as a deprecated overload: it logs a one-time warning, hands the
+  handler the whole `{ method, params }` message as before, and gives request
+  handlers a 1.x-shaped `extra` (`signal`, `requestId`, `sessionId`, `_meta`).
+  It will be removed in 3.0.
 - **Errors.** Remote JSON-RPC errors are `ProtocolError` (numeric `code`);
   local conditions are `SdkError` with a string `code`: request timeout →
   `"REQUEST_TIMEOUT"`, connection closed → `"CONNECTION_CLOSED"`. Cancelling a

src/app-bridge.ts

@@ -35,6 +35,12 @@ import {
   LoggingMessageNotificationSchema,
 } from "@modelcontextprotocol/core";
 import { EventDispatcher, MethodRegistry } from "./events.js";
+import {
+  toModernArgs,
+  type LegacyMethodSchema,
+  type LegacyNotificationHandler,
+  type LegacyRequestHandler,
+} from "./legacy-handlers.js";
 import type { ZodLiteral, ZodObject, ZodType } from "zod/v4";
 
 type MethodSchema = ZodObject<{
@@ -324,11 +330,14 @@ export class AppBridge extends Protocol<BaseContext> {
    *
    * @throws {Error} if a handler for this method is already registered.
    */
-  override setRequestHandler: Protocol<BaseContext>["setRequestHandler"] = (
+  override setRequestHandler: Protocol<BaseContext>["setRequestHandler"] &
-    method: string,
+    (<S extends LegacyMethodSchema>(
-    ...rest: unknown[]
+      /** @deprecated Pass the method name and `{ params }` instead. */
-  ) => {
+      schema: S,
-    this._methods.claim(method, "setRequestHandler");
+      handler: LegacyRequestHandler<S>,
+    ) => void) = (...args: unknown[]) => {
+    const [method, ...rest] = toModernArgs("request", args) ?? args;
+    this._methods.claim(method as string, "setRequestHandler");
     (super.setRequestHandler as unknown as UntypedHandlerSetter).call(
       this,
       method,
@@ -343,15 +352,20 @@ export class AppBridge extends Protocol<BaseContext> {
    *
    * @throws {Error} if a handler for this method is already registered.
    */
-  override setNotificationHandler: Protocol<BaseContext>["setNotificationHandler"] =
+  override setNotificationHandler: Protocol<BaseContext>["setNotificationHandler"] &
-    (method: string, ...rest: unknown[]) => {
+    (<S extends LegacyMethodSchema>(
-      this._methods.claim(method, "setNotificationHandler");
+      /** @deprecated Pass the method name and `{ params }` instead. */
-      (super.setNotificationHandler as unknown as UntypedHandlerSetter).call(
+      schema: S,
-        this,
+      handler: LegacyNotificationHandler<S>,
-        method,
+    ) => void) = (...args: unknown[]) => {
-        ...rest,
+    const [method, ...rest] = toModernArgs("notification", args) ?? args;
-      );
+    this._methods.claim(method as string, "setNotificationHandler");
-    };
+    (super.setNotificationHandler as unknown as UntypedHandlerSetter).call(
+      this,
+      method,
+      ...rest,
+    );
+  };
 
   override removeRequestHandler: Protocol<BaseContext>["removeRequestHandler"] =
     (method: string) => {

src/app.ts

@@ -24,6 +24,18 @@ import {
 import { EmptyResultSchema } from "@modelcontextprotocol/core";
 export { RESOURCE_MIME_TYPE, RESOURCE_URI_META_KEY } from "./constants.js";
 import { EventDispatcher, MethodRegistry } from "./events.js";
+import {
+  toModernArgs,
+  type LegacyMethodSchema,
+  type LegacyNotificationHandler,
+  type LegacyRequestHandler,
+} from "./legacy-handlers.js";
+export type {
+  LegacyMethodSchema,
+  LegacyNotificationHandler,
+  LegacyRequestHandler,
+  LegacyRequestHandlerExtra,
+} from "./legacy-handlers.js";
 export { EventDispatcher } from "./events.js";
 
 import { PostMessageTransport } from "./message-transport.js";
@@ -316,11 +328,14 @@ export class App extends Protocol<BaseContext> {
    *
    * @throws {Error} if a handler for this method is already registered.
    */
-  override setRequestHandler: Protocol<BaseContext>["setRequestHandler"] = (
+  override setRequestHandler: Protocol<BaseContext>["setRequestHandler"] &
-    method: string,
+    (<S extends LegacyMethodSchema>(
-    ...rest: unknown[]
+      /** @deprecated Pass the method name and `{ params }` instead. */
-  ) => {
+      schema: S,
-    this._methods.claim(method, "setRequestHandler");
+      handler: LegacyRequestHandler<S>,
+    ) => void) = (...args: unknown[]) => {
+    const [method, ...rest] = toModernArgs("request", args) ?? args;
+    this._methods.claim(method as string, "setRequestHandler");
     (super.setRequestHandler as unknown as UntypedHandlerSetter).call(
       this,
       method,
@@ -335,15 +350,20 @@ export class App extends Protocol<BaseContext> {
    *
    * @throws {Error} if a handler for this method is already registered.
    */
-  override setNotificationHandler: Protocol<BaseContext>["setNotificationHandler"] =
+  override setNotificationHandler: Protocol<BaseContext>["setNotificationHandler"] &
-    (method: string, ...rest: unknown[]) => {
+    (<S extends LegacyMethodSchema>(
-      this._methods.claim(method, "setNotificationHandler");
+      /** @deprecated Pass the method name and `{ params }` instead. */
-      (super.setNotificationHandler as unknown as UntypedHandlerSetter).call(
+      schema: S,
-        this,
+      handler: LegacyNotificationHandler<S>,
-        method,
+    ) => void) = (...args: unknown[]) => {
-        ...rest,
+    const [method, ...rest] = toModernArgs("notification", args) ?? args;
-      );
+    this._methods.claim(method as string, "setNotificationHandler");
-    };
+    (super.setNotificationHandler as unknown as UntypedHandlerSetter).call(
+      this,
+      method,
+      ...rest,
+    );
+  };
 
   override removeRequestHandler: Protocol<BaseContext>["removeRequestHandler"] =
     (method: string) => {

src/legacy-handlers.test.ts

@@ -0,0 +1,145 @@
+import { afterEach, beforeEach, describe, expect, it, spyOn } from "bun:test";
+import { InMemoryTransport, Server } from "@modelcontextprotocol/server";
+import { z } from "zod/v4";
+
+import { App } from "./app.js";
+import { AppBridge } from "./app-bridge.js";
+import {
+  McpUiInitializeRequestSchema,
+  McpUiInitializeResultSchema,
+  McpUiInitializedNotificationSchema,
+  McpUiResourceTeardownRequestSchema,
+  McpUiToolInputNotificationSchema,
+  McpUiSizeChangedNotificationSchema,
+  McpUiOpenLinkRequestSchema,
+} from "./types.js";
+
+const CustomRequestSchema = z.object({
+  method: z.literal("test/echo"),
+  params: z.object({ text: z.string() }),
+});
+
+const CustomNotificationSchema = z.object({
+  method: z.literal("test/ping"),
+  params: z.object({ n: z.number() }),
+});
+
+let warn: ReturnType<typeof spyOn>;
+beforeEach(() => {
+  warn = spyOn(console, "warn").mockImplementation(() => {});
+});
+afterEach(() => warn.mockRestore());
+
+describe("1.x setRequestHandler(Schema, handler) on App", () => {
+  it("registers a custom request and hands the handler the whole message plus a 1.x extra", async () => {
+    const app = new App({ name: "a", version: "1" }, {}, { autoResize: false });
+    const server = new Server(
+      { name: "s", version: "1" },
+      { capabilities: {} },
+    );
+    server.setRequestHandler(
+      "ui/initialize",
+      {
+        params: McpUiInitializeRequestSchema.shape.params,
+        result: McpUiInitializeResultSchema,
+      },
+      () => ({
+        protocolVersion: "2026-01-26",
+        hostCapabilities: {},
+        hostInfo: { name: "h", version: "1" },
+        hostContext: {},
+      }),
+    );
+    server.setNotificationHandler(
+      "ui/notifications/initialized",
+      { params: McpUiInitializedNotificationSchema.shape.params },
+      () => {},
+    );
+
+    let seen: unknown;
+    let seenExtra: { signal: AbortSignal; requestId: unknown } | undefined;
+    app.setRequestHandler(CustomRequestSchema, (request, extra) => {
+      seen = request;
+      seenExtra = extra;
+      return { echoed: request.params.text };
+    });
+
+    const [at, st] = InMemoryTransport.createLinkedPair();
+    await server.connect(st);
+    await app.connect(at);
+
+    const result = await server.request(
+      { method: "test/echo", params: { text: "hi" } },
+      z.object({ echoed: z.string() }),
+    );
+
+    expect(result).toEqual({ echoed: "hi" });
+    expect(seen).toEqual({ method: "test/echo", params: { text: "hi" } });
+    expect(seenExtra?.signal).toBeInstanceOf(AbortSignal);
+    expect(seenExtra?.requestId).toBeDefined();
+    expect(warn).toHaveBeenCalledTimes(1);
+    expect(String(warn.mock.calls[0][0])).toContain(
+      'setRequestHandler("test/echo", { params: Schema.shape.params }, handler)',
+    );
+
+    await app.close();
+    await server.close();
+  });
+
+  it("still throws for a method an on* setter already owns", () => {
+    const app = new App({ name: "a", version: "1" }, {}, { autoResize: false });
+    app.onteardown = async () => ({});
+    expect(() =>
+      app.setRequestHandler(
+        McpUiResourceTeardownRequestSchema,
+        async () => ({}),
+      ),
+    ).toThrow(/already registered/);
+  });
+
+  it("still throws for an event-mapped notification", () => {
+    const app = new App({ name: "a", version: "1" }, {}, { autoResize: false });
+    app.ontoolinput = () => {};
+    expect(() =>
+      app.setNotificationHandler(McpUiToolInputNotificationSchema, () => {}),
+    ).toThrow(/already registered/);
+  });
+});
+
+describe("1.x setNotificationHandler(Schema, handler) on AppBridge", () => {
+  it("registers a custom notification and hands the handler the whole message", async () => {
+    const bridge = new AppBridge(null, { name: "h", version: "1" }, {});
+    // A bare Server stands in for the View: unlike Client, connect() sends no
+    // MCP initialize, matching what a real App does on this channel.
+    const view = new Server({ name: "v", version: "1" }, { capabilities: {} });
+    let seen: unknown;
+    bridge.setNotificationHandler(CustomNotificationSchema, (n) => {
+      seen = n;
+    });
+
+    const [bt, vt] = InMemoryTransport.createLinkedPair();
+    await bridge.connect(bt);
+    await view.connect(vt);
+    await view.notification({ method: "test/ping", params: { n: 3 } });
+    await new Promise((r) => setTimeout(r, 10));
+
+    expect(seen).toEqual({ method: "test/ping", params: { n: 3 } });
+    await view.close();
+    await bridge.close();
+  });
+
+  it("still throws for a method an on* setter already owns", () => {
+    const bridge = new AppBridge(null, { name: "h", version: "1" }, {});
+    bridge.onsizechange = () => {};
+    expect(() =>
+      bridge.setNotificationHandler(
+        McpUiSizeChangedNotificationSchema,
+        () => {},
+      ),
+    ).toThrow(/already registered/);
+    bridge.onopenlink = async () => ({});
+    expect(() =>
+      bridge.setRequestHandler(McpUiOpenLinkRequestSchema, async () => ({})),
+    ).toThrow(/already registered/);
+  });
+});

src/legacy-handlers.ts

@@ -0,0 +1,94 @@
+import type { BaseContext, RequestId } from "@modelcontextprotocol/client";
+import type { ZodLiteral, ZodObject, ZodType } from "zod/v4";
+
+/**
+ * A whole-message Zod schema (`method` literal plus `params`), as accepted by
+ * the 1.x `setRequestHandler(Schema, handler)` forms.
+ */
+export type LegacyMethodSchema = ZodObject<{
+  method: ZodLiteral<string>;
+  params: ZodType;
+}>;
+
+/**
+ * The `extra` argument 1.x request handlers received.
+ *
+ * @deprecated Use the 2.x `BaseContext` (`extra.mcpReq.signal`, `extra.mcpReq.id`).
+ */
+export type LegacyRequestHandlerExtra = {
+  signal: AbortSignal;
+  requestId: RequestId;
+  sessionId?: string;
+  _meta?: BaseContext["mcpReq"]["_meta"];
+  sendRequest: BaseContext["mcpReq"]["send"];
+  sendNotification: BaseContext["mcpReq"]["notify"];
+  authInfo?: NonNullable<BaseContext["http"]>["authInfo"];
+};
+
+/** @deprecated Use `setRequestHandler("method", { params, result }, (params, ctx) => …)`. */
+export type LegacyRequestHandler<S extends LegacyMethodSchema> = (
+  request: S["_output"],
+  extra: LegacyRequestHandlerExtra,
+) => unknown;
+
+/** @deprecated Use `setNotificationHandler("method", { params }, (params) => …)`. */
+export type LegacyNotificationHandler<S extends LegacyMethodSchema> = (
+  notification: S["_output"],
+) => void | Promise<void>;
+
+/**
+ * Arguments for the 2.x three-argument `setRequestHandler` /
+ * `setNotificationHandler` form.
+ */
+type ModernArgs = [
+  method: string,
+  schemas: { params: ZodType },
+  handler: (params: unknown, ctx: BaseContext) => unknown,
+];
+
+const warned = new Set<string>();
+
+/**
+ * Translate a 1.x `(Schema, handler)` registration into the 2.x
+ * `(method, { params }, handler)` form, or return `undefined` when the call
+ * is already in the 2.x form. The 1.x handler receives the reassembled
+ * `{ method, params }` message and, for requests, a 1.x-shaped `extra`.
+ */
+export function toModernArgs(
+  kind: "request" | "notification",
+  args: unknown[],
+): ModernArgs | undefined {
+  const [first, handler] = args;
+  const shape = (first as Partial<LegacyMethodSchema> | undefined)?.shape;
+  if (typeof shape?.method?.value !== "string") return undefined;
+  const method = shape.method.value;
+  const setter =
+    kind === "request" ? "setRequestHandler" : "setNotificationHandler";
+  if (!warned.has(setter)) {
+    warned.add(setter);
+    console.warn(
+      `[ext-apps] ${setter}(Schema, handler) is deprecated; use ` +
+        `${setter}("${method}", { params: Schema.shape.params }, handler).`,
+    );
+  }
+  const call = handler as (...a: unknown[]) => unknown;
+  return [
+    method,
+    { params: shape.params },
+    kind === "request"
+      ? (params, ctx) => call({ method, params }, legacyExtra(ctx))
+      : (params) => call({ method, params }),
+  ];
+}
+
+function legacyExtra(ctx: BaseContext): LegacyRequestHandlerExtra {
+  return {
+    signal: ctx.mcpReq.signal,
+    requestId: ctx.mcpReq.id,
+    sessionId: ctx.sessionId,
+    _meta: ctx.mcpReq._meta,
+    sendRequest: ctx.mcpReq.send,
+    sendNotification: ctx.mcpReq.notify,
+    authInfo: ctx.http?.authInfo,
+  };
+}

src/types.ts

@@ -9,6 +9,55 @@
  * @see `generated/schema.test.ts` for compile-time verification
  */
 
+import type {
+  CallToolRequest,
+  CallToolResult,
+  CreateMessageRequest,
+  CreateMessageResult,
+  CreateMessageResultWithTools,
+  EmptyResult,
+  ListPromptsRequest,
+  ListPromptsResult,
+  ListResourceTemplatesRequest,
+  ListResourceTemplatesResult,
+  ListResourcesRequest,
+  ListResourcesResult,
+  ListToolsRequest,
+  ListToolsResult,
+  LoggingMessageNotification,
+  PingRequest,
+  PromptListChangedNotification,
+  ReadResourceRequest,
+  ReadResourceResult,
+  ResourceListChangedNotification,
+  ToolListChangedNotification,
+} from "@modelcontextprotocol/client";
+import type {
+  McpUiDownloadFileRequest,
+  McpUiDownloadFileResult,
+  McpUiHostContextChangedNotification,
+  McpUiInitializeRequest,
+  McpUiInitializeResult,
+  McpUiInitializedNotification,
+  McpUiMessageRequest,
+  McpUiMessageResult,
+  McpUiOpenLinkRequest,
+  McpUiOpenLinkResult,
+  McpUiRequestDisplayModeRequest,
+  McpUiRequestDisplayModeResult,
+  McpUiRequestTeardownNotification,
+  McpUiResourceTeardownRequest,
+  McpUiResourceTeardownResult,
+  McpUiSandboxProxyReadyNotification,
+  McpUiSandboxResourceReadyNotification,
+  McpUiSizeChangedNotification,
+  McpUiToolCancelledNotification,
+  McpUiToolInputNotification,
+  McpUiToolInputPartialNotification,
+  McpUiToolResultNotification,
+  McpUiUpdateModelContextRequest,
+} from "./spec.types.js";
+
 // Re-export all types from spec.types.ts
 export {
   LATEST_PROTOCOL_VERSION,
@@ -108,3 +157,71 @@ export {
   McpUiToolVisibilitySchema,
   McpUiToolMetaSchema,
 } from "./generated/schema.js";
+
+/**
+ * Union of every request an {@link app!App `App`} may send or receive.
+ *
+ * @deprecated 1.x fed this to the SDK's `Protocol` generics; SDK 2.x derives
+ * request types from the method name, so nothing consumes it anymore.
+ */
+export type AppRequest =
+  | McpUiInitializeRequest
+  | McpUiOpenLinkRequest
+  | McpUiDownloadFileRequest
+  | McpUiMessageRequest
+  | McpUiUpdateModelContextRequest
+  | McpUiResourceTeardownRequest
+  | McpUiRequestDisplayModeRequest
+  | CallToolRequest
+  | ListToolsRequest
+  | ListResourcesRequest
+  | ListResourceTemplatesRequest
+  | ReadResourceRequest
+  | ListPromptsRequest
+  | CreateMessageRequest
+  | PingRequest;
+
+/**
+ * Union of every notification an {@link app!App `App`} may send or receive.
+ *
+ * @deprecated See {@link AppRequest}.
+ */
+export type AppNotification =
+  // Sent to app
+  | McpUiHostContextChangedNotification
+  | McpUiToolInputNotification
+  | McpUiToolInputPartialNotification
+  | McpUiToolResultNotification
+  | McpUiToolCancelledNotification
+  | McpUiSandboxResourceReadyNotification
+  | ToolListChangedNotification
+  | ResourceListChangedNotification
+  | PromptListChangedNotification
+  // Received from app
+  | McpUiInitializedNotification
+  | McpUiSizeChangedNotification
+  | McpUiSandboxProxyReadyNotification
+  | McpUiRequestTeardownNotification
+  | LoggingMessageNotification;
+
+/**
+ * Union of every result an {@link app!App `App`} may send or receive.
+ *
+ * @deprecated See {@link AppRequest}.
+ */
+export type AppResult =
+  | McpUiInitializeResult
+  | McpUiOpenLinkResult
+  | McpUiDownloadFileResult
+  | McpUiMessageResult
+  | McpUiResourceTeardownResult
+  | McpUiRequestDisplayModeResult
+  | CallToolResult
+  | ListToolsResult
+  | ListResourcesResult
+  | ListResourceTemplatesResult
+  | ReadResourceResult
+  | ListPromptsResult
+  | CreateMessageResult
+  | CreateMessageResultWithTools
+  | EmptyResult;