Handles notifications without sending a response

JSON-RPC 2.0 defines notifications as messages with no id — they require no response, and sending one violates the spec. A server that sends error responses to notifications/initialized (because it tries to echo the id that isn't there) causes clients to receive unexpected extra messages, which can desync the message stream. A server that crashes on an unknown notification type (notifications/cancelled, notifications/roots/list_changed) can be triggered by any client action that emits those events, making stability fragile in real workloads.

In custom message handlers, check for the absence of id to identify notifications and return without responding.

// src/transport/handler.ts
function handleMessage(message: unknown) {
  // Notifications: no id field — process but do not respond
  if (!('id' in (message as object))) {
    const notification = message as { method: string }
    if (notification.method === 'notifications/initialized') {
      isInitialized = true
    }
    // Unknown notifications: silently ignore
    return
  }
  // Requests: have an id — must respond
  return handleRequest(message as JsonRpcRequest)
}

SDK-based servers handle this automatically — do not override the SDK's default notification handling.