fix: mcp client name

[MQ37]

Currently, Opencode uses the MCP config server name as the MCP clientInfo.name, which prevents MCP servers from easily identifying that the client is actually Opencode. This fix changes the clientInfo.name to a hardcoded value: "opencode". This ensures the Opencode MCP client is clearly identifiable by MCP servers, allowing them to adapt the features exposed based on supported specification features.

We are working on a package to address this, as the protocol does not support it yet. We would like to add Opencode, but without this change, we cannot: https://github.com/apify/mcp-client-capabilities

For example, if you configure opencode.json like this, the clientInfo.name in the MCP initialize request will be "testing-client" instead of a consistent identifier such as "opencode". Since each MCP client supports a different feature set, this makes it impossible to reliably identify Opencode.

{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "testing-client": {
      "type": "remote",
      "url": "http://localhost:3001",
      "enabled": true,
      "headers": {
        "Authorization": "Bearer MY_API_KEY"
      }
    }
  }
}

MCP initialize request with this config, which cannot be easily identified as Opencode:

{"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"testing-client","version":"1.0.0"}},"jsonrpc":"2.0","id":0}

MCP initialize request with this config patched, now clearly identifiable by the "opencode" client name:

{"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"opencode","version":"1.0.0"}},"jsonrpc":"2.0","id":0}

[rekram1-node]

this makes sense, the ai sdk defaults to "name": "ai-sdk-mcp-client" but name shouldn't be the name of mcp server, it should be name of client.