[regression]: Support MCP-Protocol-Version 2025-11-25

[adamdehaven]

When utilizing agents@0.3.3 and @modelcontextprotocol/sdk@1.25.1 when attempting to list tools or resources a MCP Server again responds with an error for unsupported protocol version:

Streamable HTTP error: Error POSTing to endpoint: 
{
  "jsonrpc": "2.0",
  "error": {
    "code": -32000,
    "message": "Bad Request: Unsupported protocol version: 2025-11-25 (supported versions: 2025-06-18, 2025-03-26, 2024-11-05, 2024-10-07)"
  },
  "id": null
}

⚠️ The issue is present for all versions of agents after 0.2.32

This was previously reported in #719 and supposedly resolved in #720; however, the issue arises again in agents@0.2.34 through 0.3.3.

To Reproduce
Steps to reproduce the behavior:

1. Install the packages listed above
2. Connect via the /mcp endpoint
3. If you don't get the error on init, attempt to list resources

Expected behavior
The protocol version should be compatable.

Version:
>= 0.2.34

[whoiskatrin]

@adamdehaven hey Adam, we haven't shipped the support for it yet: #752

See this open PR, but it's a WIP. Hopefully in the next week or so

[adamdehaven]

@whoiskatrin how can a consuming app track the proper version?

The @modelcontextprotocol/sdk exports a SUPPORTED_PROTOCOL_VERSIONS array:

import { DEFAULT_NEGOTIATED_PROTOCOL_VERSION, SUPPORTED_PROTOCOL_VERSIONS } from '@modelcontextprotocol/sdk/types.js'

Could the agents package do something similar? or where is this documented?