Add a pluggable server extension API with MCP Apps (#3003)

Co-authored-by: Max Isbey <224885523+maxisbey@users.noreply.github.com>

docs_src/apps/tutorial002.py

@@ -0,0 +1,25 @@
+from mcp.server.apps import Apps, ResourceCsp, ResourcePermissions
+from mcp.server.mcpserver import MCPServer
+
+DASHBOARD_HTML = "<!doctype html><title>Dashboard</title><canvas id='chart'></canvas>"
+
+apps = Apps()
+
+
+@apps.tool(resource_uri="ui://dashboard/app.html", visibility=["app"])
+def refresh_dashboard() -> str:
+    """Refresh the dashboard data."""
+    return "refreshed"
+
+
+apps.add_html_resource(
+    "ui://dashboard/app.html",
+    DASHBOARD_HTML,
+    title="Dashboard",
+    csp=ResourceCsp(connect_domains=["https://api.example.com"]),
+    permissions=ResourcePermissions(clipboard_write={}),
+    domain="dashboard.example.com",
+    prefers_border=True,
+)
+
+mcp = MCPServer("dashboard", extensions=[apps])