chore: import upstream snapshot with attribution

examples/stories/dual_era/server_lowlevel.py

@@ -0,0 +1,50 @@
+"""One lowlevel Server factory that serves both the 2025 handshake era and the 2026 stateless era."""
+
+from typing import Any
+
+import mcp_types as types
+from mcp_types.version import MODERN_PROTOCOL_VERSIONS
+
+from mcp.server.context import ServerRequestContext
+from mcp.server.lowlevel import Server
+from stories._hosting import run_server_from_args
+
+GREET_INPUT_SCHEMA: dict[str, Any] = {
+    "type": "object",
+    "properties": {"name": {"type": "string"}},
+    "required": ["name"],
+}
+
+
+def build_server() -> Server[Any]:
+    async def list_tools(
+        ctx: ServerRequestContext[Any], params: types.PaginatedRequestParams | None
+    ) -> types.ListToolsResult:
+        return types.ListToolsResult(
+            tools=[
+                types.Tool(
+                    name="greet",
+                    description="Greet the caller and report which protocol era served the request.",
+                    input_schema=GREET_INPUT_SCHEMA,
+                ),
+            ]
+        )
+
+    async def call_tool(ctx: ServerRequestContext[Any], params: types.CallToolRequestParams) -> types.CallToolResult:
+        assert params.name == "greet" and params.arguments is not None
+        era = "modern" if ctx.protocol_version in MODERN_PROTOCOL_VERSIONS else "legacy"
+        text = f"Hello, {params.arguments['name']}! (served on the {era} era at {ctx.protocol_version})"
+        return types.CallToolResult(content=[types.TextContent(text=text)])
+
+    # The same factory serves both eras with no configuration. Which era a request is
+    # on is decided by the entry point / transport, never by the server.
+    return Server(
+        "dual-era-example",
+        instructions="A small dual-era demo server.",
+        on_list_tools=list_tools,
+        on_call_tool=call_tool,
+    )
+
+
+if __name__ == "__main__":
+    run_server_from_args(build_server)