.NET: Support a message only AIContextProvider as an AIAgent Decorator

dotnet/samples/GettingStarted/Agents/Agent_Step14_Middleware/Program.cs

@@ -2,8 +2,9 @@
 
 // This sample shows multiple middleware layers working together with Azure OpenAI:
 // chat client (global/per-request), agent run (PII filtering and guardrails),
-// function invocation (logging and result overrides), and human-in-the-loop
-// approval workflows for sensitive function calls.
+// function invocation (logging and result overrides), human-in-the-loop
+// approval workflows for sensitive function calls, and MessageAIContextProvider
+// middleware for injecting additional context messages into the agent pipeline.
 
 using System.ComponentModel;
 using System.Text.RegularExpressions;
@@ -96,6 +97,20 @@ static string GetDateTime()
 
 Console.WriteLine($"Per-request middleware response: {response}");
 
+// MessageAIContextProvider middleware that injects additional messages into the agent request.
+// This allows any AIAgent (not just ChatClientAgent) to benefit from MessageAIContextProvider-based
+// context enrichment. Multiple providers can be passed to Use and they are called in sequence,
+// each receiving the output of the previous one.
+Console.WriteLine("\n\n=== Example 5: MessageAIContextProvider middleware ===");
+
+var contextProviderAgent = originalAgent
+    .AsBuilder()
+    .Use([new DateTimeContextProvider()])
+    .Build();
+
+var contextResponse = await contextProviderAgent.RunAsync("Is it almost time for lunch?");
+Console.WriteLine($"Context-enriched response: {contextResponse}");
+
 // Function invocation middleware that logs before and after function calls.
 async ValueTask<object?> FunctionCallMiddleware(AIAgent agent, FunctionInvocationContext context, Func<FunctionInvocationContext, CancellationToken, ValueTask<object?>> next, CancellationToken cancellationToken)
 {
@@ -259,3 +274,23 @@ async Task<ChatResponse> PerRequestChatClientMiddleware(IEnumerable<ChatMessage>
 
     return response;
 }
+
+/// <summary>
+/// A <see cref="MessageAIContextProvider"/> that injects the current date and time into the agent's context.
+/// This is a simple example of how to use a MessageAIContextProvider to enrich agent messages
+/// via the <see cref="AIAgentBuilder.Use(MessageAIContextProvider[])"/> extension method.
+/// </summary>
+internal sealed class DateTimeContextProvider : MessageAIContextProvider
+{
+    protected override ValueTask<IEnumerable<ChatMessage>> ProvideMessagesAsync(
+        InvokingContext context,
+        CancellationToken cancellationToken = default)
+    {
+        Console.WriteLine("DateTimeContextProvider - Injecting current date/time context");
+
+        return new ValueTask<IEnumerable<ChatMessage>>(
+            [
+                new ChatMessage(ChatRole.User, $"For reference, the current date and time is: {DateTimeOffset.Now}")
+            ]);
+    }
+}

dotnet/samples/GettingStarted/Agents/Agent_Step14_Middleware/README.md

@@ -14,6 +14,7 @@ This sample demonstrates how to add middleware to intercept:
 5. Per‑request chat client middleware
 6. Per‑request function pipeline with approval
 7. Combining agent‑level and per‑request middleware
+8. MessageAIContextProvider middleware via `AIAgentBuilder.Use(...)` for injecting additional context messages
 
 ## Function Invocation Middleware
 

dotnet/samples/GettingStarted/Agents/Agent_Step20_AdditionalAIContext/Program.cs

@@ -150,13 +150,12 @@ private static void AddTodoItem(AgentSession? session, string item)
     }
 
     /// <summary>
-    /// An <see cref="AIContextProvider"/> which searches for upcoming calendar events and adds them to the AI context.
+    /// A <see cref="MessageAIContextProvider"/> which searches for upcoming calendar events and adds them to the AI context.
     /// </summary>
-    internal sealed class CalendarSearchAIContextProvider(Func<Task<string[]>> loadNextThreeCalendarEvents) : AIContextProvider
+    internal sealed class CalendarSearchAIContextProvider(Func<Task<string[]>> loadNextThreeCalendarEvents) : MessageAIContextProvider
     {
-        protected override async ValueTask<AIContext> InvokingCoreAsync(InvokingContext context, CancellationToken cancellationToken = default)
+        protected override async ValueTask<IEnumerable<MEAI.ChatMessage>> ProvideMessagesAsync(InvokingContext context, CancellationToken cancellationToken = default)
         {
-            var inputContext = context.AIContext;
             var events = await loadNextThreeCalendarEvents();
 
             StringBuilder outputMessageBuilder = new();
@@ -166,18 +165,7 @@ protected override async ValueTask<AIContext> InvokingCoreAsync(InvokingContext
                 outputMessageBuilder.AppendLine($" - {calendarEvent}");
             }
 
-            return new()
-            {
-                Instructions = inputContext.Instructions,
-                Messages =
-                    (inputContext.Messages ?? [])
-                    .Concat(
-                    [
-                        new MEAI.ChatMessage(ChatRole.User, outputMessageBuilder.ToString()).WithAgentRequestMessageSource(AgentRequestMessageSourceType.AIContextProvider, this.GetType().FullName!)
-                    ])
-                    .ToList(),
-                Tools = inputContext.Tools
-            };
+            return [new MEAI.ChatMessage(ChatRole.User, outputMessageBuilder.ToString())];
         }
     }
 }

dotnet/src/Microsoft.Agents.AI.Abstractions/AIContextProvider.cs

@@ -34,9 +34,6 @@ public abstract class AIContextProvider
     private static IEnumerable<ChatMessage> DefaultExternalOnlyFilter(IEnumerable<ChatMessage> messages)
         => messages.Where(m => m.GetAgentRequestMessageSourceType() == AgentRequestMessageSourceType.External);
 
-    private readonly Func<IEnumerable<ChatMessage>, IEnumerable<ChatMessage>> _provideInputMessageFilter;
-    private readonly Func<IEnumerable<ChatMessage>, IEnumerable<ChatMessage>> _storeInputMessageFilter;
-
     /// <summary>
     /// Initializes a new instance of the <see cref="AIContextProvider"/> class.
     /// </summary>
@@ -46,10 +43,20 @@ protected AIContextProvider(
         Func<IEnumerable<ChatMessage>, IEnumerable<ChatMessage>>? provideInputMessageFilter = null,
         Func<IEnumerable<ChatMessage>, IEnumerable<ChatMessage>>? storeInputMessageFilter = null)
     {
-        this._provideInputMessageFilter = provideInputMessageFilter ?? DefaultExternalOnlyFilter;
-        this._storeInputMessageFilter = storeInputMessageFilter ?? DefaultExternalOnlyFilter;
+        this.ProvideInputMessageFilter = provideInputMessageFilter ?? DefaultExternalOnlyFilter;
+        this.StoreInputMessageFilter = storeInputMessageFilter ?? DefaultExternalOnlyFilter;
     }
 
+    /// <summary>
+    /// Gets the filter function to apply to input messages before providing context via <see cref="ProvideAIContextAsync"/>.
+    /// </summary>
+    protected Func<IEnumerable<ChatMessage>, IEnumerable<ChatMessage>> ProvideInputMessageFilter { get; }
+
+    /// <summary>
+    /// Gets the filter function to apply to request messages before storing context via <see cref="StoreAIContextAsync"/>.
+    /// </summary>
+    protected Func<IEnumerable<ChatMessage>, IEnumerable<ChatMessage>> StoreInputMessageFilter { get; }
+
     /// <summary>
     /// Gets the key used to store the provider state in the <see cref="AgentSession.StateBag"/>.
     /// </summary>
@@ -120,7 +127,7 @@ protected virtual async ValueTask<AIContext> InvokingCoreAsync(InvokingContext c
             new AIContext
             {
                 Instructions = inputContext.Instructions,
-                Messages = inputContext.Messages is not null ? this._provideInputMessageFilter(inputContext.Messages) : null,
+                Messages = inputContext.Messages is not null ? this.ProvideInputMessageFilter(inputContext.Messages) : null,
                 Tools = inputContext.Tools
             });
 
@@ -254,7 +261,7 @@ protected virtual ValueTask InvokedCoreAsync(InvokedContext context, Cancellatio
             return default;
         }
 
-        var subContext = new InvokedContext(context.Agent, context.Session, this._storeInputMessageFilter(context.RequestMessages), context.ResponseMessages!);
+        var subContext = new InvokedContext(context.Agent, context.Session, this.StoreInputMessageFilter(context.RequestMessages), context.ResponseMessages!);
         return this.StoreAIContextAsync(subContext, cancellationToken);
     }