Upgrade the assistant to a harness

using System.ComponentModel;
using FabrCore.Core;
using FabrCore.Sdk;

[AgentAlias("researcher")]
[Description("Researches a question end to end and reports back.")]
[FabrCoreCapabilities("Breaks a research goal into tracked steps, delegates lookups to specialist agents, and reports a consolidated answer.")]
public class ResearcherAgent : FabrCoreAgentProxy
{
    private FabrCoreHarnessResult harness = null!;

    public ResearcherAgent(AgentConfiguration config, IServiceProvider serviceProvider, IFabrCoreAgentHost fabrcoreAgentHost)
        : base(config, serviceProvider, fabrcoreAgentHost) { }

    public override async Task OnInitialize()
    {
        var tools = await ResolveConfiguredToolsAsync();
        harness = await CreateFabrCoreHarnessAgent(config.Models ?? "default", "main", tools);
    }

    public override async Task<AgentMessage> OnMessage(AgentMessage message)
    {
        var run = await harness.RunAsync(message);

        var response = message.Response();
        response.Message = run.Text;
        return response;
    }
}

public override async Task<AgentMessage> OnMessage(AgentMessage message)
{
    SetStatusMessage("Planning...");

    var run = await harness.RunAsync(message);
    var text = run.Text;

    // Delegations stranded by a restart — see references/durability.md.
    if (harness.DescribeLostDelegations() is { } lost)
    {
        text += $"{Environment.NewLine}{Environment.NewLine}{lost}";
    }

    var remaining = await harness.GetRemainingTodosAsync();
    if (remaining.Count > 0)
    {
        text += $"{Environment.NewLine}{Environment.NewLine}Not completed within the iteration budget:{Environment.NewLine}"
            + string.Join(Environment.NewLine, remaining.Select(item => $"- {item.Title}"));
    }

    SetStatusMessage(string.Empty);

    var response = message.Response();
    response.Message = text;
    return response;
}