Support MCP 2026-07-28 Multi Round-Trip Requests (input_required)

Describe the feature or problem you'd like to solve

Copilot does not support the protocol version 2026-07-28 and thus MRTR for URL elicitation fail for server not supporting legacy (2025-era) fallback

Proposed solution

Copilot CLI should support the MCP 2026-07-28 Multi Round-Trip Request (MRTR) mechanism, including input_required, requestState, and URL-mode elicitation.

Problem

I am running Copilot CLI 1.0.83 against an MCP server that implements only MCP 2026-07-28 (1.0.83 is the latest version of Copilot at the time of writing). The server has legacy MCP compatibility disabled and therefore does not support the 2025-era server --> client elicitation mechanism.

Expected behavior

For a 2026-07-28 MCP connection, Copilot CLI should:

• send protocol version 2026-07-28 on initialize
• Receive resultType: "input_required" from tools/call.
• Handle the embedded URL elicitation and present/launch the URL for the user.
• Collect the result of the elicitation.
• Retry the original tools/call as a new JSON-RPC request.

Actual behavior

With Copilot CLI 1.0.83, the client sends protocol version 2025-11-25 on initialize.

{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "initialize",
    "params": {
        "protocolVersion": "2025-11-25",
        "capabilities": {
            "sampling": {},
            "elicitation": {
                "form": {},
                "url": {}
            }
        },
        "clientInfo": {
            "name": "copilot-cli",
            "version": "0.0.0"
        }
    }
}

(interesting: clientInfo states 0.0.0 instead of 1.0.83)

Subsequently, Copilot sends notifications/initialized and tools/list:

{
    "jsonrpc": "2.0",
    "method": "notifications/initialized"
}

{
    "jsonrpc": "2.0",
    "id": 2,
    "method": "tools/list",
    "params": {
        "_meta": {
            "progressToken": 0
        }
    }
}

Then, I ask for a tool called url_elicitation. Copilot sends the payload:

{
    "jsonrpc": "2.0",
    "id": 4,
    "method": "tools/call",
    "params": {
        "_meta": {
            "progressToken": 0
        },
        "arguments": {},
        "name": "url_elicitation"
    }
}

MCP server responds with the error as the tool handler returns input-required result which is not supported by protocol 2025-11-25:

{
    "jsonrpc": "2.0",
    "id": 4,
    "error": {
        "code": -32603,
        "message": "Handler for tools/call returned an input-required result, but this request is served on protocol revision 2025-11-25, which has no input_required vocabulary"
    }
}

Note that the request headers set by Copilot include:
"mcp-protocol-version": "2025-11-25".

Note that the MCP server intentionally has the legacy compatibility/shim disabled.

Requested support

Please add native Copilot CLI support for:

• MCP protocol 2026-07-28
• Multi Round-Trip Requests (MRTR)
• requestState round-tripping
• URL-mode elicitation
• Retrying tools/call after elicitation

Please provide info about the roadmap.

Example prompts or workflows

No response

Additional context

No response

Start by tracing the MCP initialize and tools/call entry points described in the issue, including protocol-version negotiation and URL-mode elicitation. Verify how input_required and requestState are represented, then confirm that the original tools/call is retried as a new JSON-RPC request after the elicitation result is collected.