Allow extending agent with additional properties

src/Agents/AgentExtensions.cs

@@ -23,4 +23,14 @@ public static ChatResponse AsChatResponse(this AgentRunResponse response)
 
         return chatResponse;
     }
+
+    extension(AIAgent agent)
+    {
+        /// <summary>Gets the emoji associated with the agent, if any.</summary>
+        public string? Emoji => agent is not IHasAdditionalProperties additional
+            ? null
+            : additional.AdditionalProperties is null
+            ? null
+            : additional.AdditionalProperties.TryGetValue("Emoji", out var value) ? value as string : null;
+    }
 }

src/Agents/ConfigurableAIAgent.cs

@@ -15,7 +15,7 @@ namespace Devlooped.Agents.AI;
 /// A configuration-driven <see cref="AIAgent"/> which monitors configuration changes and 
 /// re-applies them to the inner agent automatically.
 /// </summary>
-public sealed partial class ConfigurableAIAgent : AIAgent, IDisposable
+public sealed partial class ConfigurableAIAgent : AIAgent, IHasAdditionalProperties, IDisposable
 {
     readonly IServiceProvider services;
     readonly IConfiguration configuration;
@@ -57,6 +57,9 @@ Type t when typeof(AIAgentMetadata).IsAssignableFrom(t) => metadata,
         _ => agent.GetService(serviceType, serviceKey)
     };
 
+    /// <inheritdoc/>
+    public AdditionalPropertiesDictionary? AdditionalProperties { get; set; }
+
     /// <inheritdoc/>
     public override string Id => agent.Id;
     /// <inheritdoc/>
@@ -89,6 +92,20 @@ public override IAsyncEnumerable<AgentRunResponseUpdate> RunStreamingAsync(IEnum
         options?.Description = options?.Description?.Dedent();
         options?.Instructions = options?.Instructions?.Dedent();
 
+        var properties = configSection.Get<AdditionalPropertiesDictionary>();
+        if (properties is not null)
+        {
+            properties?.Remove(nameof(AgentClientOptions.Name));
+            properties?.Remove(nameof(AgentClientOptions.Description));
+            properties?.Remove(nameof(AgentClientOptions.Instructions));
+            properties?.Remove(nameof(AgentClientOptions.Client));
+            properties?.Remove(nameof(AgentClientOptions.Model));
+            properties?.Remove(nameof(AgentClientOptions.Use));
+            properties?.Remove(nameof(AgentClientOptions.Tools));
+
+            AdditionalProperties = properties;
+        }
+
         // If there was a custom id, we must validate it didn't change since that's not supported.
         if (configuration[$"{section}:name"] is { } newname && newname != name)
             throw new InvalidOperationException($"The name of a configured agent cannot be changed at runtime. Expected '{name}' but was '{newname}'.");

src/Agents/IHasAdditionalProperties.cs

@@ -0,0 +1,10 @@
+using Microsoft.Extensions.AI;
+
+namespace Devlooped.Agents.AI;
+
+/// <summary>Indicates that the instance can have additional properties associated with it.</summary>
+public interface IHasAdditionalProperties
+{
+    /// <summary>Gets or sets any additional properties associated with the instance.</summary>
+    AdditionalPropertiesDictionary? AdditionalProperties { get; set; }
+}

src/Tests/ConfigurableAgentTests.cs

@@ -25,6 +25,7 @@ public void CanConfigureAgent()
             ["ai:agents:bot:description"] = "Helpful chat agent",
             ["ai:agents:bot:instructions"] = "You are a helpful chat agent.",
             ["ai:agents:bot:options:temperature"] = "0.5",
+            ["ai:agents:bot:emoji"] = "🤖",
         });
 
         builder.AddAIAgents();
@@ -36,6 +37,10 @@ public void CanConfigureAgent()
         Assert.Equal("chat", agent.Name);
         Assert.Equal("chat", agent.DisplayName);
         Assert.Equal("Helpful chat agent", agent.Description);
+
+        var additional = Assert.IsType<IHasAdditionalProperties>(agent, exactMatch: false);
+        Assert.Equal("🤖", additional.AdditionalProperties?["emoji"]?.ToString());
+        Assert.Equal("🤖", agent.Emoji);
     }
 
     [Fact]