feat(debug-server): add interactive debug server example (#321)

* feat(examples): add debug-server example

A comprehensive debug/development server for testing MCP Apps SDK features:
- Vanilla TypeScript UI with collapsible panels
- Message visualization (sent, received, errors)
- Server tool calling interface
- Multiple tool endpoints for testing

* refactor(debug-server): convert to React

- Replace vanilla TypeScript with React components
- Add comprehensive Host Styles panel showing all CSS variables grouped by category
- Use React hooks (useApp, useHostStyles, useAutoResize)
- Cleaner state management with useReducer for event log
- Collapsible sections for better organization
- CSS modules for scoped styling

* fix(debug-server): correct server name in main.ts

* Revert "refactor(debug-server): convert to React"

This reverts commit 5d22d2daa9a98ba412892447202ef10fbdb62f5b.

* fix(debug-server): update default values for multipleBlocks and includeMeta

* fix(debug-server): correct serve script and server name

- serve script now runs main.ts instead of server.ts
- Updated server name to 'Debug Server'
- Fixed npx command in comment

* fix: increase maxHeight to 6000px and add tools capability to debug app

- basic-host: Increase maxHeight from 600 to 6000px
- debug-server: Add tools capability to enable oncalltool/onlisttools handlers

* fix(debug-server): use consistent callback names for event tracking

Event types now match callback names (ontoolinput, ontoolresult, etc.)
so the Callback Status panel shows correct counts and payloads.

* feat(debug-server): add Update (Image) button for model context

* feat(debug-server): add expandable event log entries

- Click on any event log row to expand/collapse
- Arrow indicator rotates when expanded
- Full JSON payload shown indented in pre block
- Max height with scroll for large payloads

* style(debug-server): format long line in fullPayload function

* test(debug-server): add to E2E tests and screenshot specs

* chore: regenerate package-lock.json for cross-platform compatibility

* update dep

examples/debug-server/main.ts

@@ -0,0 +1,94 @@
+/**
+ * Entry point for running the MCP server.
+ * Run with: npx mcp-server-debug
+ * Or: node dist/index.js [--stdio]
+ */
+
+/**
+ * Shared utilities for running MCP servers with Streamable HTTP transport.
+ */
+
+import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
+import { createMcpExpressApp } from "@modelcontextprotocol/sdk/server/express.js";
+import type { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
+import { StreamableHTTPServerTransport } from "@modelcontextprotocol/sdk/server/streamableHttp.js";
+import cors from "cors";
+import type { Request, Response } from "express";
+import { createServer } from "./server.js";
+
+export interface ServerOptions {
+  port: number;
+  name?: string;
+}
+
+/**
+ * Starts an MCP server with Streamable HTTP transport in stateless mode.
+ *
+ * @param createServer - Factory function that creates a new McpServer instance per request.
+ * @param options - Server configuration options.
+ */
+export async function startServer(
+  createServer: () => McpServer,
+  options: ServerOptions,
+): Promise<void> {
+  const { port, name = "MCP Server" } = options;
+
+  const app = createMcpExpressApp({ host: "0.0.0.0" });
+  app.use(cors());
+
+  app.all("/mcp", async (req: Request, res: Response) => {
+    const server = createServer();
+    const transport = new StreamableHTTPServerTransport({
+      sessionIdGenerator: undefined,
+    });
+
+    res.on("close", () => {
+      transport.close().catch(() => {});
+      server.close().catch(() => {});
+    });
+
+    try {
+      await server.connect(transport);
+      await transport.handleRequest(req, res, req.body);
+    } catch (error) {
+      console.error("MCP error:", error);
+      if (!res.headersSent) {
+        res.status(500).json({
+          jsonrpc: "2.0",
+          error: { code: -32603, message: "Internal server error" },
+          id: null,
+        });
+      }
+    }
+  });
+
+  const httpServer = app.listen(port, (err) => {
+    if (err) {
+      console.error("Failed to start server:", err);
+      process.exit(1);
+    }
+    console.log(`${name} listening on http://localhost:${port}/mcp`);
+  });
+
+  const shutdown = () => {
+    console.log("\nShutting down...");
+    httpServer.close(() => process.exit(0));
+  };
+
+  process.on("SIGINT", shutdown);
+  process.on("SIGTERM", shutdown);
+}
+
+async function main() {
+  if (process.argv.includes("--stdio")) {
+    await createServer().connect(new StdioServerTransport());
+  } else {
+    const port = parseInt(process.env.PORT ?? "3110", 10);
+    await startServer(createServer, { port, name: "Debug Server" });
+  }
+}
+
+main().catch((e) => {
+  console.error(e);
+  process.exit(1);
+});