Strongly-typed requests with named arguments produce empty params object with SystemTextJsonFormatter

net9.0, StreamJsonRpc 2.22.11

Interface declaration

public interface TestInterface
{
    public Task<int> add(int a, int b);
}

Strongly-typed request with named arguments with JsonMessageFormatter

Pipe pipe = new();

var formatter = new JsonMessageFormatter();
var handler = new LengthHeaderMessageHandler(pipe.Writer, pipe.Reader, formatter);
var jsonRpc = new JsonRpc(handler);

jsonRpc.TraceSource.Listeners.Add(new ConsoleTraceListener());
jsonRpc.TraceSource.Switch.Level = SourceLevels.Verbose;

jsonRpc.StartListening();

JsonRpcProxyOptions JsonRpcProxyOptions = new()
{
    ServerRequiresNamedArguments = true
};

TestInterface testInterface = jsonRpc.Attach<TestInterface>(JsonRpcProxyOptions);
await testInterface.add(123, 456);

Partial console output

JsonRpc Verbose: 8 : Sent: {
  "jsonrpc": "2.0",
  "id": 2,
  "method": "add",
  "params": {
    "a": 123,
    "b": 456
  }
}

Strongly-typed request with named arguments with SystemTextJsonFormatter

Pipe pipe = new();

var formatter = new SystemTextJsonFormatter();
var handler = new LengthHeaderMessageHandler(pipe.Writer, pipe.Reader, formatter);
var jsonRpc = new JsonRpc(handler);

jsonRpc.TraceSource.Listeners.Add(new ConsoleTraceListener());
jsonRpc.TraceSource.Switch.Level = SourceLevels.Verbose;

jsonRpc.StartListening();

JsonRpcProxyOptions JsonRpcProxyOptions = new()
{
    ServerRequiresNamedArguments = true
};

TestInterface testInterface = jsonRpc.Attach<TestInterface>(JsonRpcProxyOptions);
await testInterface.add(123, 456);

Partial console output

JsonRpc Verbose: 8 : Sent: {"jsonrpc":"2.0","id":2,"method":"add","params":{}}

Start by reproducing the strongly-typed named-argument request with SystemTextJsonFormatter and compare its output with JsonMessageFormatter. Inspect the JsonRpc.Attach proxy path, JsonRpcProxyOptions, and the two formatter entry points to find why parameter names are omitted. Done means the System.Text.Json request contains "a": 123 and "b": 456, with coverage for this repro.