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

Guide: name @modelcontextprotocol/express in the server-author row, say
the two SDKs share no types rather than "do not interoperate" (they speak
the same wire protocol), note zod 4.0/4.1 lack ~standard.jsonSchema, list
the full 1.x-shaped extra, cover tool callbacks in the handler-context
bullet, document that the double-registration guard now covers the base
Protocol's notifications/progress and notifications/cancelled handlers,
mention ResourceNotFoundError, add the Express row to the import map, and
add a "What stays the same" section.

The @deprecated tag on the legacy setRequestHandler / setNotificationHandler
overload sat on the parameter inside an intersection type, which TypeScript
does not report. The overload now comes from LegacyRequestHandlerSetter /
LegacyNotificationHandlerSetter, named types with a documented call
signature, so editors flag the 1.x call and not the 2.x forms.

README links to the quickstart use the lowercase slug typedoc emits.

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