.NET: Support dynamic agent resolution in AG-UI endpoints (MapAGUI with factory delegate)

[mattbrailsford]

Summary

The current MapAGUI extension method only accepts a pre-created AIAgent instance, which doesn't support scenarios where the agent needs to be resolved dynamically at request time (e.g., multi-tenant applications, agent selection by ID/alias from a database).

Current API

public static IEndpointConventionBuilder MapAGUI(
    this IEndpointRouteBuilder endpoints,
    string pattern,
    AIAgent aiAgent)  // Pre-created instance

Problem

For dynamic agent resolution scenarios like:

• POST /agents/{agentId}/stream - resolve agent by ID from database
• Multi-tenant applications where agent configuration varies per tenant
• Agent marketplaces where users select from multiple agents

We cannot use MapAGUI because the agent must be resolved at request time, not at startup.

Additionally, the types needed to implement this ourselves are internal:

• RunAgentInput - cannot use for model binding
• AGUIServerSentEventsResult - cannot return from custom endpoint

This forces consumers to reimplement AG-UI request/response handling.

Proposed Solution

Add factory delegate overload

public static IEndpointConventionBuilder MapAGUI(
    this IEndpointRouteBuilder endpoints,
    string pattern,
    Func<HttpContext, CancellationToken, Task<AIAgent?>> agentFactory)

Usage:

endpoints.MapAGUI("/agents/{agentId}/stream", async (httpContext, ct) =>
{
    var agentId = httpContext.GetRouteValue("agentId")?.ToString();
    return await agentResolver.ResolveAsync(agentId, ct);
});

Environment

• Package: Microsoft.Agents.AI.Hosting.AGUI.AspNetCore v1.0.0-preview.251219.1
• Framework: .NET 10

[TheEagleByte]

I've put together a PR for this which should address everything! Hopefully we can get it merged soon.

[avogiatzis]

@TheEagleByte appreciate the work you've done on the PR, where there any developments on the architectural discussions? We're also looking to adopt AGUI but the static agent is an issue as we're looking to build agents dynamically, fetching configurations from the Database etc.

[TheEagleByte]

@avogiatzis Unfortunately there's been no movement or follow up, just a workaround that isn't ideal. At least it is workable for now, but ideally this gets merged in for a more standard approach. It's a shame this is getting held up for so long with no movement.

I agree, this is really a crucial feature when you need to do agent based access control (in the one use case I have). Really don't know why such a crucial and power feature would be held up.