[Question/Bug?] A2A agent response in Playground displays raw JSON, not parsed text + Metadata

[techgeniuswang]

Hi LiteLLM team,

I'm running into an issue with A2A agents in the Proxy Playground (LiteLLM v1.81.14 + a2a-sdk >=0.3.22 added to dependencies).

Problem description
When I send a message to my custom A2A agent via the Playground (using /v1/a2a/{agent_id}/message/send endpoint), the response is always displayed as raw JSON in the UI, instead of:

• Rendering the text content as the main reply
• Showing the A2A Metadata panel below (Task ID, Context ID, status, timestamp, etc.)

I have tried both common response formats recommended in the docs:

1. kind: "message" (simple sync reply)

{
  "jsonrpc": "2.0",
  "id": "...",
  "result": {
    "kind": "message",
    "messageId": "...",
    "role": "agent",
    "parts": [
      {
        "kind": "text",
        "text": "Welcome call agent demo ----> TEST12345"
      }
    ]
  }
}

2. kind: "task" + artifacts (preferred for metadata)

{
  "jsonrpc": "2.0",
  "id": "...",
  "result": {
    "kind": "task",
    "id": "...",
    "contextId": "...",
    "status": {
      "state": "completed",
      "timestamp": "2026-02-24T03:15:06.385578+00:00"
    },
    "artifacts": [
      {
        "artifactId": "...",
        "name": "response",
        "parts": [
          {
            "kind": "text",
            "text": "Welcome call agent demo ----> TEST12345"
          }
        ]
      }
    ]
  }
}

Both formats return 200 OK when tested with curl / raw HTTP, and the JSON is correct. But in Playground, it's always raw JSON dump, no text extraction, no Metadata panel.

Additional context:

• LiteLLM version: 1.81.14
• Dependencies include: litellm[proxy]>=1.81.0, a2a-sdk>=0.3.22, prisma>=0.15.0
• The agent is a simple LangGraph node returning the above dict directly.
• Proxy logs confirm it's handling message/send (not stream).
• I saw issue [Bug]: Playground endpoint /message/send incorrectly uses streaming method message/stream #19021 about Playground misusing streaming logic for /message/send, but according to my understanding it should be fixed/closed by now? (If not, is there a workaround?)

Questions

1. Is there any specific format or extra field required for Playground to render text + Metadata correctly in v1.81.14?
2. Does Playground have known issues with rendering A2A responses in this version? Any recommended workaround (e.g. force SSE even for sync, custom UI, etc.)?
3. Should I upgrade to a newer version / main branch? Or add some config flag for playground rendering?

Thanks for any help or pointers — really appreciate the great work on A2A support!Best,

[techgeniuswang]

screen shot of above issue