Return Invalid Request for an empty JSON-RPC batch

[royalpinto007]

Problem

handleMcpRequest treats an empty JSON array as a batch with no responses and returns HTTP 202. Under JSON-RPC 2.0, an empty batch is invalid and should return an Invalid Request error.

Relevant code: src/mcp.ts.

Expected behavior

A request body of [] should return a JSON-RPC error with code -32600, rather than a successful empty response.

Acceptance criteria

• Detect an empty batch before dispatch.
• Return a valid JSON-RPC Invalid Request error with id null.
• Keep notification-only non-empty batches returning no response.
• Add request-level tests covering empty batches and notification-only batches.

[vsolano9]

I’ll take this. I’ll add request-level regression coverage for both the empty-batch error and the existing notification-only 202 behavior, then return a JSON-RPC -32600 error with id: null before dispatching an empty batch.