## Description

When the LiteLLM `/mcp/` endpoint receives a JSON-RPC request that's rejected at the protocol layer (e.g. an unknown method like `tools/totally_made_up`, or malformed params), the proxy returns a JSON-RPC error response to the caller — but **no `standard_logging_object` is produced**. No callback fires, no spend log entry is written, no audit trail exists.

This creates a blind spot for:

- Audit/compliance pipelines that expect every inbound request to produce a record. - Abuse/malformed-traffic detection. - Operators investigating a client that's hammering the proxy with bad requests.

## Repro

Tested on `ghcr.io/berriai/litellm:main-v1.81.14-stable`.

1. POST a JSON-RPC request with an unknown method: ```bash curl -s -X POST 'http://localhost:4000/mcp/' \ -H 'Authorization: Bearer sk-1234' \ -H 'Content-Type: application/json' \ -H 'Accept: application/json, text/event-stream' \ -d '{"jsonrpc":"2.0","id":1,"method":"tools/totally_made_up","params":{}}' ``` 2. Caller receives: ```json {"jsonrpc":"2.0","id":1, "error":{"code":-32602,"message":"Invalid request parameters","data":""}} ``` 3. Search verbose proxy logs / Langf…