dotnet: MapAGUI supports on-demand agent selection (addressing copilot comments)

Author: halllo

dotnet/samples/AGUIClientServer/AGUIDojoServer/Program.cs

@@ -40,10 +40,11 @@
 var jsonOptions = app.Services.GetRequiredService<IOptions<Microsoft.AspNetCore.Http.Json.JsonOptions>>();
 app.MapAGUI("/shared_state", ChatClientAgentFactory.CreateSharedState(jsonOptions.Value.SerializerOptions));
 
-app.MapAGUI("/agents/{agentId}", async (context) =>
+// Map an AG-UI agent endpoint with per-request agent selection based on route parameter
+app.MapAGUI("/agents/{agentId}", (context) =>
 {
-    var agentId = context.Request.RouteValues["agentId"]?.ToString() ?? string.Empty;
-    return agentId switch
+    string agentId = context.Request.RouteValues["agentId"]?.ToString() ?? string.Empty;
+    return ValueTask.FromResult(agentId switch
     {
         "agentic_chat" => ChatClientAgentFactory.CreateAgenticChat(),
         "backend_tool_rendering" => ChatClientAgentFactory.CreateBackendToolRendering(),
@@ -52,7 +53,7 @@
         "agentic_generative_ui" => ChatClientAgentFactory.CreateAgenticUI(),
         "shared_state" => ChatClientAgentFactory.CreateSharedState(jsonOptions.Value.SerializerOptions),
         _ => throw new ArgumentException($"Unknown agent ID: {agentId}"),
-    };
+    });
 });
 
 await app.RunAsync();

dotnet/samples/AGUIClientServer/AGUIServer/Program.cs

@@ -4,6 +4,7 @@
 using AGUIServer;
 using Azure.AI.OpenAI;
 using Azure.Identity;
+using Microsoft.Agents.AI;
 using Microsoft.Agents.AI.Hosting.AGUI.AspNetCore;
 using Microsoft.Extensions.AI;
 using OpenAI;
@@ -48,14 +49,16 @@
 // Map the AG-UI agent endpoint
 app.MapAGUI("/", agent);
 
-app.MapAGUI("/agents/{agentId}", async (context) =>
+// Map an AG-UI agent endpoint with per-request agent selection based on route parameter
+app.MapAGUI("/agents/{agentId}", (context) =>
 {
-    var agentId = context.Request.RouteValues["agentId"]?.ToString() ?? string.Empty;
-    return agentId switch
+    string agentId = context.Request.RouteValues["agentId"]?.ToString() ?? string.Empty;
+    AIAgent selectedAgent = agentId switch
     {
         "0" => agent,
         _ => throw new ArgumentException($"Unknown agent ID: {agentId}"),
     };
+    return ValueTask.FromResult(selectedAgent);
 });
 
 await app.RunAsync();

dotnet/src/Microsoft.Agents.AI.Hosting.AGUI.AspNetCore/AGUIEndpointRouteBuilderExtensions.cs

@@ -82,6 +82,10 @@ public static IEndpointConventionBuilder MapAGUI(
 
             // Determine the agent to use
             var aiAgent = await aiAgentSelector(context).ConfigureAwait(false);
+            if (aiAgent is null)
+            {
+                return Results.BadRequest("Agent could not be determined.");
+            }
 
             // Run the agent and convert to AG-UI events
             var events = aiAgent.RunStreamingAsync(