.Net: BugFix TryGetFunction + FunctionInvocationFilter when using IChatClient (microsoft#12405)

### Motivation and Context

- Fixes microsoft#12378

Co-authored-by: SergeyMenshykh <68852919+SergeyMenshykh@users.noreply.github.com>

Author: rogerbarreto

dotnet/src/SemanticKernel.Abstractions/AI/ChatClient/KernelFunctionInvokingChatClient.cs

@@ -102,8 +102,7 @@ await autoFunctionInvocationFilters[index].OnAutoFunctionInvocationAsync(
                 // Note that we explicitly do not use executionSettings here; those pertain to the all-up operation and not necessarily to any
                 // further calls made as part of this function invocation. In particular, we must not use function calling settings naively here,
                 // as the called function could in turn telling the model about itself as a possible candidate for invocation.
-                result = await autoContext.AIFunction.InvokeAsync(autoContext.Arguments, cancellationToken).ConfigureAwait(false);
-                ctx.Result = new FunctionResult(ctx.Function, result);
+                ctx.Result = await autoContext.Function.InvokeAsync(kernelChatOptions.Kernel, autoContext.Arguments, cancellationToken).ConfigureAwait(false);
             }).ConfigureAwait(false);
         result = autoContext.Result.GetValue<object>();
 

dotnet/src/SemanticKernel.Core/Functions/DefaultKernelPlugin.cs

@@ -3,6 +3,8 @@
 using System;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
+using System.Linq;
+using Microsoft.Extensions.AI;
 
 namespace Microsoft.SemanticKernel;
 
@@ -41,8 +43,27 @@ internal DefaultKernelPlugin(string name, string? description, IEnumerable<Kerne
     public override int FunctionCount => this._functions.Count;
 
     /// <inheritdoc/>
-    public override bool TryGetFunction(string name, [NotNullWhen(true)] out KernelFunction? function) =>
-        this._functions.TryGetValue(name, out function);
+    public override bool TryGetFunction(string name, [NotNullWhen(true)] out KernelFunction? function)
+    {
+        if (this._functions.TryGetValue(name, out function))
+        {
+            return true;
+        }
+
+        if (this._functions.Count == 0 || name.Length <= this.Name.Length)
+        {
+            // The function name is too short to have the plugin name aborting the search.
+            function = null;
+            return false;
+        }
+
+        // When a kernel function is used as an ai function by IChatClients it needs to be discoverable by the FQN.
+        function = (KernelFunction?)this._functions.Values
+            .Select(f => f as AIFunction)
+            .FirstOrDefault(aiFunction => aiFunction.Name == name);
+
+        return function is not null;
+    }
 
     /// <inheritdoc/>
     public override IEnumerator<KernelFunction> GetEnumerator() => this._functions.Values.GetEnumerator();