Orleans grain observer (IGrainObserver) which returns results

ObserverWithReturn.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net6.0</TargetFramework>
    <RootNamespace>ObserverWithReturn</RootNamespace>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.Hosting" Version="6.0.1" />
    <PackageReference Include="Microsoft.Orleans.CodeGenerator.MSBuild" Version="3.6.0" />
    <PackageReference Include="Microsoft.Orleans.Server" Version="3.6.0" />
  </ItemGroup>

</Project>

Program.cs

using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Orleans;
using Orleans.Hosting;

namespace ObserverWithReturn;

class Program
{
    static async Task Main(string[] args)
    {
        using var host = Host.CreateDefaultBuilder()
            .UseOrleans(siloBuilder =>
            {
                siloBuilder.UseLocalhostClustering();
            }).Build();

        await host.StartAsync();

        var client = host.Services.GetRequiredService<IGrainFactory>();

        var observer = new MyObserver("Hope this is what you're after.");
        var observerReference = await client.CreateObjectReference<IMyObserver>(observer);

        var grain = client.GetGrain<IMyGrain>("testing");
        var result = await grain.CallMeBack(observerReference);

        Console.WriteLine($"Client received: \"{result}\"");
        Console.ReadLine();

        await host.StopAsync();
    }
}

public interface IMyObserver : IGrainObserver
{
    ValueTask<string> GetGreeting(string input);
}

public class MyObserver : IMyObserver
{
    private readonly string _customMessage;

    public MyObserver(string customMessage) => _customMessage = customMessage;

    public ValueTask<string> GetGreeting(string input) => new($"Hello {input}! {_customMessage}");
}

public interface IMyGrain : IGrainWithStringKey
{
    Task<string> CallMeBack(IMyObserver observer);
}

public class MyGrain : Grain, IMyGrain
{
    public async Task<string> CallMeBack(IMyObserver observer)
    {
        var result = await observer.GetGreeting(this.GetPrimaryKeyString());
        return $"Grain received: \"{result}\"";
    }
}