Update ActivityInputConverter for Activities with FunctionContext-only parameters (#2806)

* Update ActivityInputConverter.cs

* update result to unhandled

Author: nytian

src/Worker.Extensions.DurableTask/ActivityInputConverter.cs

@@ -25,6 +25,13 @@ public ValueTask<ConversionResult> ConvertAsync(ConverterContext context)
             throw new ArgumentNullException(nameof(context));
         }
 
+        // Special handling for FunctionContext
+        // This addresses cases where the activity function has only FunctionContext as a parameter.
+        if (context.TargetType == typeof(FunctionContext))
+        {
+            return new(ConversionResult.Unhandled());
+        }
+
         if (context.Source is null)
         {
             return new(ConversionResult.Success(null));

src/Worker.Extensions.DurableTask/ActivityTriggerAttribute.cs

@@ -15,7 +15,7 @@ namespace Microsoft.Azure.Functions.Worker;
 [AttributeUsage(AttributeTargets.Parameter)]
 [DebuggerDisplay("{Activity}")]
 [InputConverter(typeof(ActivityInputConverter))]
-[ConverterFallbackBehavior(ConverterFallbackBehavior.Disallow)]
+[ConverterFallbackBehavior(ConverterFallbackBehavior.Allow)]
 public sealed class ActivityTriggerAttribute : TriggerBindingAttribute
 {
     /// <summary>