chore: import upstream snapshot with attribution

examples/stories/legacy_routing/server_lowlevel.py

@@ -0,0 +1,48 @@
+"""Exported era classifier (lowlevel API): the same dual-era app + CORS — the predicate stays in `server.py`."""
+
+from typing import Any
+
+import mcp_types as types
+from mcp_types.version import MODERN_PROTOCOL_VERSIONS
+from starlette.applications import Starlette
+from starlette.middleware.cors import CORSMiddleware
+
+from mcp.server.context import ServerRequestContext
+from mcp.server.lowlevel import Server
+from stories._hosting import NO_DNS_REBIND, run_app_from_args
+
+from .server import MCP_ALLOWED_HEADERS, MCP_ALLOWED_METHODS, MCP_EXPOSED_HEADERS
+
+WHICH_ARM = types.Tool(
+    name="which_arm",
+    description="Report which era the built-in router dispatched this request to.",
+    input_schema={"type": "object", "properties": {}},
+)
+
+
+def build_app() -> Starlette:
+    async def list_tools(
+        ctx: ServerRequestContext[Any], params: types.PaginatedRequestParams | None
+    ) -> types.ListToolsResult:
+        return types.ListToolsResult(tools=[WHICH_ARM])
+
+    async def call_tool(ctx: ServerRequestContext[Any], params: types.CallToolRequestParams) -> types.CallToolResult:
+        assert params.name == "which_arm"
+        arm = "modern" if ctx.protocol_version in MODERN_PROTOCOL_VERSIONS else "legacy"
+        return types.CallToolResult(content=[types.TextContent(text=arm)])
+
+    server = Server("legacy-routing-example", on_list_tools=list_tools, on_call_tool=call_tool)
+
+    app = server.streamable_http_app(transport_security=NO_DNS_REBIND)
+    app.add_middleware(
+        CORSMiddleware,
+        allow_origins=["*"],
+        allow_methods=MCP_ALLOWED_METHODS,
+        allow_headers=MCP_ALLOWED_HEADERS,
+        expose_headers=MCP_EXPOSED_HEADERS,
+    )
+    return app
+
+
+if __name__ == "__main__":
+    run_app_from_args(build_app)