docs: rebuild the v2 documentation around a task-based page tree (#2397)

docs/serving/fastify.md

@@ -0,0 +1,90 @@
+---
+shape: how-to
+---
+# Serve with Fastify
+
+```sh
+npm install @modelcontextprotocol/server @modelcontextprotocol/fastify @modelcontextprotocol/node fastify
+```
+
+## Mount the handler
+
+`createMcpHandler` turns a server factory into a web-standard HTTP handler, and `toNodeHandler` adapts it once to Node's `(req, res)` — a Fastify route hands it `request.raw` and `reply.raw`. `createMcpFastifyApp` is `Fastify()` with DNS rebinding protection already applied.
+
+```ts source="../../examples/guides/serving/fastify.examples.ts#createMcpFastifyApp_mount"
+import { createMcpFastifyApp } from '@modelcontextprotocol/fastify';
+import { toNodeHandler } from '@modelcontextprotocol/node';
+import { createMcpHandler, McpServer } from '@modelcontextprotocol/server';
+import * as z from 'zod/v4';
+
+const handler = createMcpHandler(() => {
+    const server = new McpServer({ name: 'notes', version: '1.0.0' });
+    server.registerTool('add-note', { description: 'Append a note', inputSchema: z.object({ text: z.string() }) }, async ({ text }) => ({
+        content: [{ type: 'text', text: `Saved: ${text}` }]
+    }));
+    return server;
+});
+
+const app = createMcpFastifyApp();
+const node = toNodeHandler(handler);
+app.all('/mcp', (request, reply) => node(request.raw, reply.raw, request.body));
+```
+
+`app` is an ordinary Fastify instance with one route — `/mcp` answers every MCP request — and nothing is listening yet. The factory runs once per request, so a fresh `McpServer` serves every call: [Serve over HTTP](./http.md#understand-the-per-request-factory) covers that model.
+
+## Protect against DNS rebinding
+
+A malicious page can DNS-rebind its own domain to `127.0.0.1` and reach a localhost server as if it were same-origin. `createMcpFastifyApp` validates the `Host` and `Origin` headers against that: with the default `127.0.0.1` bind (and `localhost` / `::1`), a request carrying a non-localhost value gets `403` before your handler runs.
+
+Binding to all interfaces drops that default — name the hosts you serve instead.
+
+```ts source="../../examples/guides/serving/fastify.examples.ts#createMcpFastifyApp_allowedHosts"
+const publicApp = createMcpFastifyApp({ host: '0.0.0.0', allowedHosts: ['api.example.com'] });
+```
+
+`allowedHosts` and `allowedOrigins` take hostnames, port-agnostic. A request without an `Origin` header always passes, so MCP clients outside a browser are unaffected.
+
+## Forward auth and the parsed body
+
+Fastify parses JSON bodies itself, so `request.body` is already the parsed body — passing it as `toNodeHandler`'s third argument keeps the adapter from re-reading the consumed stream. Auth rides on the Node request: set `auth` on `request.raw` and `toNodeHandler` forwards it, so handlers read it as `ctx.http.authInfo`.
+
+```ts source="../../examples/guides/serving/fastify.examples.ts#toNodeHandler_authInfo"
+publicApp.all('/mcp', async (request, reply) => {
+    const auth = await verifyToken(request.headers.authorization);
+    return node(Object.assign(request.raw, { auth }), reply.raw, request.body);
+});
+```
+
+`verifyToken` is your token verification. [Authorization](./authorization.md) covers verifying bearer tokens and serving the OAuth metadata documents.
+
+## Run it and verify
+
+Add the listen line and start the process (`npx tsx server.ts`).
+
+```ts source="../../examples/guides/serving/fastify.examples.ts#createMcpFastifyApp_listen"
+await app.listen({ port: 3000 });
+```
+
+POST a `tools/list` request to the endpoint.
+
+```sh
+curl -s -X POST http://127.0.0.1:3000/mcp \
+  -H 'Content-Type: application/json' \
+  -H 'Accept: application/json, text/event-stream' \
+  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list"}'
+```
+
+The response is a single SSE `message` event carrying the `tools/list` result:
+
+```
+event: message
+data: {"result":{"tools":[{"name":"add-note","description":"Append a note","inputSchema":{"type":"object","$schema":"https://json-schema.org/draft/2020-12/schema","properties":{"text":{"type":"string"}},"required":["text"]}}]},"jsonrpc":"2.0","id":1}
+```
+
+## Recap
+
+- One install line, one file: `createMcpFastifyApp()` plus `app.all('/mcp', …)` over `toNodeHandler(createMcpHandler(factory))`.
+- A fresh server instance from your factory serves every request.
+- Fastify already parsed `request.body`; pass it as `toNodeHandler`'s third argument.
+- The default `127.0.0.1` bind validates `Host` and `Origin`; pass `allowedHosts` when binding to `0.0.0.0`.
+- Set `auth` on the raw Node request; `toNodeHandler` forwards it as `ctx.http.authInfo`.