chore: import upstream snapshot with attribution

examples/stories/dual_era/server.py

@@ -0,0 +1,25 @@
+"""One MCPServer factory that serves both the 2025 handshake era and the 2026 stateless era."""
+
+from mcp_types.version import MODERN_PROTOCOL_VERSIONS
+
+from mcp.server.mcpserver import Context, MCPServer
+from stories._hosting import run_server_from_args
+
+
+def build_server() -> MCPServer:
+    # 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.
+    mcp = MCPServer("dual-era-example", instructions="A small dual-era demo server.")
+
+    @mcp.tool()
+    async def greet(name: str, ctx: Context) -> str:
+        """Greet the caller and report which protocol era served the request."""
+        pv = ctx.request_context.protocol_version
+        era = "modern" if pv in MODERN_PROTOCOL_VERSIONS else "legacy"
+        return f"Hello, {name}! (served on the {era} era at {pv})"
+
+    return mcp
+
+
+if __name__ == "__main__":
+    run_server_from_args(build_server)