[DAP] Working with a server which doesn't set "seq" property in some responses

Hi,
I am trying get the DAP client working with vscode-lldb server.
Unfortunately, this server sends some responses without seq property set. For example, it sends the the following initialize response:

{
  "type": "response",
  "request_seq": 1,
  "success": true,
  "command": "initialize",
  "body": {
    //...
  }
}

Given such a response, the DapReceiver fails with "No sequence given":

            if (!request.TryGetValue("seq", out var id))
            {
                yield return new InvalidRequest(null, "No sequence given");
                yield break;
            }

I patched the code like this:

            if (!request.TryGetValue("seq", out var id))
            {
                id = 0;
            }

-- and the client worked.

Given that VS Code works with such a server behavior without any problems, I think it is reasonable to "fix" this in the client.

I tried to replace DapReceiver with my inherited class to modify this behavior without changing the library, but didn't find a way to change the service container registration code.

Could you please advice on how to better resolve this issue? Is my fix suitable for the official library packages? Maybe we could log warnings in such cases, but allow the responses without seq?

Start with the DapReceiver response-validation code shown in the issue and trace how missing seq values become InvalidRequest responses. Check the DAP response handling and service-container registration before deciding whether responses without seq should be accepted or warned about; done means the vscode-lldb initialize response no longer causes the client to fail, with behavior covered by an appropriate regression test.