docs: add elicitation usage example

docs/ADVANCED.md

@@ -56,40 +56,99 @@ export { handler as GET, handler as POST, handler as DELETE };
 
 ```typescript
 interface Config {
-  redisUrl?: string;    // Redis connection URL for pub/sub
-  basePath?: string;    // Base path for MCP endpoints
+  redisUrl?: string; // Redis connection URL for pub/sub
+  basePath?: string; // Base path for MCP endpoints
   maxDuration?: number; // Maximum duration for SSE connections (seconds)
   verboseLogs?: boolean; // Enable debug logging
 }
 ```
 
-## Nuxt Usage
+## Elicitation
+
+Elicitation requires a bidirectional transport so the server can ask the client
+for input while a tool is running. Use the SSE transport with Redis enabled and
+export all three HTTP methods:
 
 ```typescript
-// server/api/mcp/[transport].ts
+// app/api/[transport]/route.ts
 import { createMcpHandler } from "mcp-handler";
-import { fromWebHandler } from "h3";
 import { z } from "zod";
 
 const handler = createMcpHandler(
   (server) => {
     server.registerTool(
-      "roll_dice",
+      "quote_product",
       {
-        title: "Roll Dice",
-        description: "Roll a dice with a specified number of sides.",
-        inputSchema: { sides: z.number().int().min(2) },
+        title: "Quote Product",
+        description: "Ask the user which product should be quoted.",
+        inputSchema: {},
       },
-      async ({ sides }) => {
-        const value = 1 + Math.floor(Math.random() * sides);
+      async () => {
+        const result = await server.server.elicitInput({
+          message: "Which product should be quoted?",
+          requestedSchema: {
+            type: "object",
+            properties: {
+              productName: {
+                type: "string",
+                title: "Product",
+                enum: ["starter", "pro", "enterprise"],
+              },
+            },
+            required: ["productName"],
+          },
+        });
+
+        const productName = result.content?.productName;
         return {
-          content: [{ type: "text", text: `🎲 You rolled a ${value}!` }],
+          content: [
+            {
+              type: "text",
+              text: `Creating a quote for ${productName}.`,
+            },
+          ],
         };
       }
     );
   },
-  {}
+  {},
+  {
+    basePath: "/api",
+    redisUrl: process.env.REDIS_URL,
+  }
 );
 
+export { handler as GET, handler as POST, handler as DELETE };
+```
+
+Clients must support elicitation. If a client only sends Streamable HTTP `POST`
+requests and does not keep a server-to-client channel open, the server cannot
+deliver the elicitation request.
+
+## Nuxt Usage
+
+```typescript
+// server/api/mcp/[transport].ts
+import { createMcpHandler } from "mcp-handler";
+import { fromWebHandler } from "h3";
+import { z } from "zod";
+
+const handler = createMcpHandler((server) => {
+  server.registerTool(
+    "roll_dice",
+    {
+      title: "Roll Dice",
+      description: "Roll a dice with a specified number of sides.",
+      inputSchema: { sides: z.number().int().min(2) },
+    },
+    async ({ sides }) => {
+      const value = 1 + Math.floor(Math.random() * sides);
+      return {
+        content: [{ type: "text", text: `🎲 You rolled a ${value}!` }],
+      };
+    }
+  );
+}, {});
+
 export default fromWebHandler(handler);
 ```