Enhanced IAgent Model

[jeremydmiller]

cc @mysticmind

Today IAgent (the running background processes which would include the projection / subscriptions to marten now, Wolverine's backing for virtual agents)
is this:

public interface IAgent : IHostedService
{
    /// <summary>
    ///     Unique identification for this agent within the Wolverine system
    /// </summary>
    Uri Uri { get; }
    
    // Added in 3.0, doesn't really do much for you
    AgentStatus Status { get; }
}

public enum AgentStatus
{
    Started,
    Stopped
}

Two ideas for extension:

• For maybe 3.0 and definitely by 4.0, how about we add IHealthCheck directly into the IAgent model?
• Have the IAgent s expose a description of what metrics and/or Otel spans they export. Marten's projections export a counter on events processed, a histogram of the "gap", and spans for loading, grouping, and execution. Maybe that can be used to integrate inside of Critter Watch with PromQL calls

[mysticmind]

Yes, above should be a good starting point.