# Bug: `/a2a/{id}/message/send` returns `-32603 "Stream consumed"` on JSON-RPC POST

## Summary

LiteLLM proxy's A2A endpoints (`POST /a2a/{agent_id}` and `POST /a2a/{agent_id}/message/send`) return a JSON-RPC 2.0 error response `{"jsonrpc":"2.0","id":null,"error":{"code":-32603,"message":"Internal error: Stream consumed"}}` when invoked via raw HTTP POST (curl).

Affects: LiteLLM `main` branch as of 2026-05-13, observed on Docker image `ghcr.io/berriai/litellm-non_root:main-stable` (running locally as v1.83.10-equivalent with `a2a-sdk==0.3.24` bundled).

## Repro

1. Register an AgentCard via `POST /v1/agents` with admin master-key — succeeds, AgentCard visible at `GET /v1/agents`, dashboard playground works. 2. From outside the proxy, POST a JSON-RPC `message/send` request:

```bash TRACE=$(uuidgen) curl -fsSk -X POST \ -H "Authorization: Bearer ${VK}" \ -H "x-litellm-trace-id: ${TRACE}" \ -H "Content-Type: application/json" \ "https://${LITELLM_HOST}/a2a/${AGENT_ID}/message/send" \ -d "{ \"jsonrpc\": \"2.0\", \"id\": \"$(uuidgen)\", \"method\": \"message/send\", \"params\": { \"message\": { \"kind\": \"message\", \"messageId\": \"$…