fix(mcp): handle null JSON-RPC request payloads safely

When the MCP client sends a malformed or null top-level request, prevent the AttributeError on request.get() by explicitly validating that the request is a dictionary. Returns standard JSON-RPC Error -32600 (Invalid Request) instead of crashing the server.

mempalace/mcp_server.py

@@ -1968,6 +1968,8 @@ SUPPORTED_PROTOCOL_VERSIONS = [
 
 
 def handle_request(request):
+    if not isinstance(request, dict):
+        return {"jsonrpc": "2.0", "error": {"code": -32600, "message": "Invalid Request"}}
     method = request.get("method") or ""
     params = request.get("params") or {}
     req_id = request.get("id")