Migration guide fixes and editor-visible deprecation for the 1.x handler form

README.md

@@ -11,7 +11,7 @@
     <br /><br />
     <a href="#why-mcp-apps">Why</a>
     ·
-    <a href="https://apps.extensions.modelcontextprotocol.io/api/documents/Quickstart.html">Quickstart</a>
+    <a href="https://apps.extensions.modelcontextprotocol.io/api/documents/quickstart.html">Quickstart</a>
     ·
     <a href="https://apps.extensions.modelcontextprotocol.io/api/">API Docs</a>
     ·
@@ -151,7 +151,7 @@ in a 1.x host and a 2.x host renders 1.x Views. See the
 when upgrading from 1.x.
 
 **New here?** Start with the
-[Quickstart Guide](https://apps.extensions.modelcontextprotocol.io/api/documents/Quickstart.html)
+[Quickstart Guide](https://apps.extensions.modelcontextprotocol.io/api/documents/quickstart.html)
 to build your first MCP App.
 
 ## Using the SDK
@@ -272,7 +272,7 @@ point your client at a local build:
 
 ## Resources
 
-- [Quickstart Guide](https://apps.extensions.modelcontextprotocol.io/api/documents/Quickstart.html)
+- [Quickstart Guide](https://apps.extensions.modelcontextprotocol.io/api/documents/quickstart.html)
 - [API Documentation](https://apps.extensions.modelcontextprotocol.io/api/)
 - [Specification (2026-01-26)](https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/2026-01-26/apps.mdx)
   ([Draft](https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/draft/apps.mdx))

docs/migrate-to-2.md

@@ -17,14 +17,22 @@ The `ui/*` messages exchanged over the iframe channel are byte-identical to
 1.x. A 2.x View runs in a 1.x host and a 2.x host renders 1.x Views. The only
 host-side deltas are in error responses (see below).
 
+## What stays the same
+
+`App` / `AppBridge` constructors, the `on*` setters, `addEventListener`,
+`callServerTool`, `readServerResource`, `registerAppResource`, the React hooks
+and the `_meta.ui.resourceUri` handling are unchanged. Published `.d.ts` files
+now resolve under `moduleResolution: NodeNext` / `Node16` without workarounds
+(#705).
+
 ## Peer dependencies by role
 
-| Role                | Install                                                                                                                      |
-| ------------------- | ---------------------------------------------------------------------------------------------------------------------------- |
-| View author         | `@modelcontextprotocol/ext-apps`, `@modelcontextprotocol/client@^2.0.0`, `zod@^4.2.0` (+ `react`/`react-dom` for `./react`)  |
-| Host author         | same as View author                                                                                                          |
-| MCP server author   | View author packages + `@modelcontextprotocol/server@^2.0.0`; `@modelcontextprotocol/node` and `express` for HTTP transports |
-| CDN / `*-with-deps` | nothing extra: `./app-with-deps` and `./react-with-deps` bundle client, core and zod (about 25% larger than the 1.x bundles) |
+| Role                | Install                                                                                                                                                                                                                                                       |
+| ------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
+| View author         | `@modelcontextprotocol/ext-apps`, `@modelcontextprotocol/client@^2.0.0`, `zod@^4.2.0` (+ `react`/`react-dom` for `./react`)                                                                                                                                   |
+| Host author         | same as View author                                                                                                                                                                                                                                           |
+| MCP server author   | View author packages + `@modelcontextprotocol/server@^2.0.0`; for HTTP transports also `@modelcontextprotocol/node@^2.0.0` (`NodeStreamableHTTPServerTransport`) and `@modelcontextprotocol/express@^2.0.0` (`createMcpExpressApp`, which peers on `express`) |
+| CDN / `*-with-deps` | nothing extra: `./app-with-deps` and `./react-with-deps` bundle client, core and zod (about 25% larger than the 1.x bundles)                                                                                                                                  |
 
 `@modelcontextprotocol/client` is a required peer (`App` and `AppBridge` extend
 its `Protocol` class); `@modelcontextprotocol/core` is a required peer that `client` already depends on, so npm installs it without you listing it;
@@ -35,18 +43,23 @@ its `Protocol` class); `@modelcontextprotocol/core` is a required peer that `cli
 
 - **Peer packages.** `@modelcontextprotocol/sdk@^1` is replaced by the split
   2.x packages above, all at `^2.0.0`. Remove the 1.x package from your
-  project; the two SDKs do not interoperate.
+  project: the two SDKs share no classes or types (a 1.x `McpError` or
+  `Client` cannot be passed to 2.x code), even though they speak the same
+  wire protocol.
 - **zod 3 dropped.** The peer range is `zod@^4.2.0`. Tool schemas must
-  implement Standard JSON Schema (`~standard.jsonSchema`): zod v4, ArkType,
-  Valibot. Raw zod shapes (`{ q: z.string() }`) still work with
+  implement Standard JSON Schema (`~standard.jsonSchema`): zod 4.2+, ArkType,
+  Valibot. zod 4.0 and 4.1 do not expose `~standard.jsonSchema` and are
+  rejected too. 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` is gone; use the SDK's `Protocol`. The `AppRequest`,
   `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`.
+- **Handler context.** Custom request handlers, `registerAppTool` callbacks
+  (server) and `app.registerTool` callbacks (View) receive the SDK 2.x
+  context: `extra.signal` → `extra.mcpReq.signal`, `extra.requestId` →
+  `extra.mcpReq.id`; `extra.sessionId` is unchanged and `extra.authInfo`
+  moved to `extra.http?.authInfo`.
 - **`setRequestHandler` / `setNotificationHandler` take method names.**
   `app.setRequestHandler(SomeRequestSchema, handler)` becomes
   `app.setRequestHandler("some/method", { params: SomeParamsSchema }, (params, ctx) => …)`
@@ -55,14 +68,23 @@ its `Protocol` class); `@modelcontextprotocol/core` is a required peer that `cli
   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.
+  handlers a 1.x-shaped `extra` (`signal`, `requestId`, `sessionId`, `_meta`,
+  `sendRequest`, `sendNotification`, `authInfo`; exported as
+  `LegacyRequestHandlerExtra`). It will be removed in 3.0.
+- **Double-registration guard covers the SDK's own handlers.** Registering a
+  handler for `notifications/progress` or `notifications/cancelled` (which
+  the base `Protocol` already owns) now throws `already registered`, as
+  `ping` and the `on*`-owned methods did in 1.x. Use `addEventListener` or
+  the SDK's progress callbacks instead of replacing these.
 - **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
   request with an `AbortSignal` also rejects with `"REQUEST_TIMEOUT"` (the
   message is the abort reason). Messages no longer carry the `MCP error N:`
   prefix.
+  A resource-not-found reply that carries `data.uri` arrives as
+  `ResourceNotFoundError` (a `ProtocolError` subclass, `code` `-32602`, with a
+  `.uri` getter).
 
 ## Host-side wire deltas
 
@@ -98,8 +120,9 @@ The published `./schema.json` export is regenerated from the 2.x core schemas:
 2. Replace `sdk/...` imports with the split packages (`sdk/server/mcp.js` →
    `@modelcontextprotocol/server`, `sdk/server/streamableHttp.js` →
    `NodeStreamableHTTPServerTransport` from `@modelcontextprotocol/node`,
-   `sdk/server/stdio.js` → `@modelcontextprotocol/server/stdio`, `sdk/types.js`
-   → `@modelcontextprotocol/client` or `server` for the types,
+   `sdk/server/stdio.js` → `@modelcontextprotocol/server/stdio`, hand-written
+   Express routing → `createMcpExpressApp` from `@modelcontextprotocol/express`,
+   `sdk/types.js` → `@modelcontextprotocol/client` or `server` for the types,
    `@modelcontextprotocol/core` for the zod schemas).
 3. Wrap raw zod shapes with `z.object({...})`.
 4. Update custom handlers to the `extra.mcpReq.*` context and method-keyed

src/app-bridge.ts

@@ -37,9 +37,8 @@ import {
 import { EventDispatcher, MethodRegistry } from "./events.js";
 import {
   toModernArgs,
-  type LegacyMethodSchema,
-  type LegacyNotificationHandler,
-  type LegacyRequestHandler,
+  type LegacyNotificationHandlerSetter,
+  type LegacyRequestHandlerSetter,
 } from "./legacy-handlers.js";
 import type { ZodLiteral, ZodObject, ZodType } from "zod/v4";
 
@@ -330,12 +329,9 @@ export class AppBridge extends Protocol<BaseContext> {
    *
    * @throws {Error} if a handler for this method is already registered.
    */
-  override setRequestHandler: Protocol<BaseContext>["setRequestHandler"] &
-    (<S extends LegacyMethodSchema>(
-      /** @deprecated Pass the method name and `{ params }` instead. */
-      schema: S,
-      handler: LegacyRequestHandler<S>,
-    ) => void) = (...args: unknown[]) => {
+  override setRequestHandler: LegacyRequestHandlerSetter<
+    Protocol<BaseContext>["setRequestHandler"]
+  > = (...args: unknown[]) => {
     const [method, ...rest] = toModernArgs("request", args) ?? args;
     this._methods.claim(method as string, "setRequestHandler");
     (super.setRequestHandler as unknown as UntypedHandlerSetter).call(
@@ -352,12 +348,9 @@ export class AppBridge extends Protocol<BaseContext> {
    *
    * @throws {Error} if a handler for this method is already registered.
    */
-  override setNotificationHandler: Protocol<BaseContext>["setNotificationHandler"] &
-    (<S extends LegacyMethodSchema>(
-      /** @deprecated Pass the method name and `{ params }` instead. */
-      schema: S,
-      handler: LegacyNotificationHandler<S>,
-    ) => void) = (...args: unknown[]) => {
+  override setNotificationHandler: LegacyNotificationHandlerSetter<
+    Protocol<BaseContext>["setNotificationHandler"]
+  > = (...args: unknown[]) => {
     const [method, ...rest] = toModernArgs("notification", args) ?? args;
     this._methods.claim(method as string, "setNotificationHandler");
     (super.setNotificationHandler as unknown as UntypedHandlerSetter).call(

src/app.ts

@@ -26,15 +26,16 @@ 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,
+  type LegacyNotificationHandlerSetter,
+  type LegacyRequestHandlerSetter,
 } from "./legacy-handlers.js";
 export type {
   LegacyMethodSchema,
   LegacyNotificationHandler,
+  LegacyNotificationHandlerSetter,
   LegacyRequestHandler,
   LegacyRequestHandlerExtra,
+  LegacyRequestHandlerSetter,
 } from "./legacy-handlers.js";
 export { EventDispatcher } from "./events.js";
 
@@ -328,12 +329,9 @@ export class App extends Protocol<BaseContext> {
    *
    * @throws {Error} if a handler for this method is already registered.
    */
-  override setRequestHandler: Protocol<BaseContext>["setRequestHandler"] &
-    (<S extends LegacyMethodSchema>(
-      /** @deprecated Pass the method name and `{ params }` instead. */
-      schema: S,
-      handler: LegacyRequestHandler<S>,
-    ) => void) = (...args: unknown[]) => {
+  override setRequestHandler: LegacyRequestHandlerSetter<
+    Protocol<BaseContext>["setRequestHandler"]
+  > = (...args: unknown[]) => {
     const [method, ...rest] = toModernArgs("request", args) ?? args;
     this._methods.claim(method as string, "setRequestHandler");
     (super.setRequestHandler as unknown as UntypedHandlerSetter).call(
@@ -350,12 +348,9 @@ export class App extends Protocol<BaseContext> {
    *
    * @throws {Error} if a handler for this method is already registered.
    */
-  override setNotificationHandler: Protocol<BaseContext>["setNotificationHandler"] &
-    (<S extends LegacyMethodSchema>(
-      /** @deprecated Pass the method name and `{ params }` instead. */
-      schema: S,
-      handler: LegacyNotificationHandler<S>,
-    ) => void) = (...args: unknown[]) => {
+  override setNotificationHandler: LegacyNotificationHandlerSetter<
+    Protocol<BaseContext>["setNotificationHandler"]
+  > = (...args: unknown[]) => {
     const [method, ...rest] = toModernArgs("notification", args) ?? args;
     this._methods.claim(method as string, "setNotificationHandler");
     (super.setNotificationHandler as unknown as UntypedHandlerSetter).call(

src/legacy-handlers.ts

@@ -36,6 +36,33 @@ export type LegacyNotificationHandler<S extends LegacyMethodSchema> = (
   notification: S["_output"],
 ) => void | Promise<void>;
 
+/**
+ * `setRequestHandler` with the 1.x `(Schema, handler)` form kept as a
+ * deprecated overload next to the 2.x forms in `Modern`.
+ */
+export type LegacyRequestHandlerSetter<Modern> = Modern & {
+  /**
+   * @deprecated 1.x form. Pass the method name and `{ params }` instead;
+   * removed in 3.0.
+   */
+  <S extends LegacyMethodSchema>(
+    schema: S,
+    handler: LegacyRequestHandler<S>,
+  ): void;
+};
+
+/** `setNotificationHandler` counterpart of {@link LegacyRequestHandlerSetter}. */
+export type LegacyNotificationHandlerSetter<Modern> = Modern & {
+  /**
+   * @deprecated 1.x form. Pass the method name and `{ params }` instead;
+   * removed in 3.0.
+   */
+  <S extends LegacyMethodSchema>(
+    schema: S,
+    handler: LegacyNotificationHandler<S>,
+  ): void;
+};
+
 /**
  * Arguments for the 2.x three-argument `setRequestHandler` /
  * `setNotificationHandler` form.