JSON-RPC envelope errors use `id:null` even when the request id is present

[cclabadmin]

The Ruby SDK server returns JSON-RPC error responses for several malformed JSON-RPC envelope cases, but those responses use id:null even when the incoming payload contains a concrete request id.

From a JSON-RPC client's perspective, the original request remains pending because no response with the matching id arrives. The server itself remains usable and continues to process subsequent requests.

Tested with:

• stable release v0.18.0 (3ff237a02c0792bbfbcacef5e37c0c7529c1f2a5)
• Transports: stdio and Streamable HTTP

To Reproduce

1. Start a server over stdio or Streamable HTTP.
2. Complete a normal initialization flow.
3. Send these requests in isolation:

{"jsonrpc":"1.0","id":3,"method":"ping","params":{}}
{"id":4,"method":"ping","params":{}}
{"jsonrpc":"2.0","id":8,"method":12345,"params":{}}

Expected behavior

For valid JSON payloads where the top-level request id is present and recoverable, it would be helpful for the JSON-RPC error response to preserve that id so clients can correlate the response with the pending request.

Logs

Case	Sent	Server response
wrong jsonrpc version	{"jsonrpc":"1.0","id":3,...}	{"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"Invalid Request","data":"JSON-RPC version must be 2.0"}}
missing jsonrpc field	{"id":4,"method":"ping",...}	{"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"Invalid Request","data":"JSON-RPC version must be 2.0"}}
method as number	{"jsonrpc":"2.0","id":8,"method":12345,...}	{"jsonrpc":"2.0","id":null,"error":{"code":-32600,"message":"Invalid Request","data":"Method name must be a string and not start with \"rpc.\""}}

In all three cases, subsequent pings received correct responses — the server remained usable.