refactor: Rename AddFanInEdge to AddFanInBarrierEdge

This will prevent a breaking change later when we introduce a programmable FanIn edge, analogous to the FanOut edge's EdgeSelector.

The goal, in the long run is to support a number of different FanIn scenarios, with naive FanIn (no barrier) by default, similar to FanOut.

Author: lokitoth

dotnet/samples/GettingStarted/Workflows/Agents/WorkflowAsAnAgent/WorkflowFactory.cs

@@ -24,7 +24,7 @@ internal static Workflow BuildWorkflow(IChatClient chatClient)
         // Build the workflow by adding executors and connecting them
         return new WorkflowBuilder(startExecutor)
             .AddFanOutEdge(startExecutor, [frenchAgent, englishAgent])
-            .AddFanInEdge([frenchAgent, englishAgent], aggregationExecutor)
+            .AddFanInBarrierEdge([frenchAgent, englishAgent], aggregationExecutor)
             .WithOutputFrom(aggregationExecutor)
             .Build();
     }

dotnet/samples/GettingStarted/Workflows/Concurrent/Concurrent/Program.cs

@@ -56,7 +56,7 @@ private static async Task Main()
         // Build the workflow by adding executors and connecting them
         var workflow = new WorkflowBuilder(startExecutor)
             .AddFanOutEdge(startExecutor, [physicist, chemist])
-            .AddFanInEdge([physicist, chemist], aggregationExecutor)
+            .AddFanInBarrierEdge([physicist, chemist], aggregationExecutor)
             .WithOutputFrom(aggregationExecutor)
             .Build();
 

dotnet/samples/GettingStarted/Workflows/Concurrent/MapReduce/Program.cs

@@ -63,9 +63,9 @@ public static Workflow BuildWorkflow()
         // Step 4: Build the concurrent workflow with fan-out/fan-in pattern
         return new WorkflowBuilder(splitter)
             .AddFanOutEdge(splitter, [.. mappers])         // Split -> many mappers
-            .AddFanInEdge([.. mappers], shuffler)          // All mappers -> shuffle
+            .AddFanInBarrierEdge([.. mappers], shuffler)          // All mappers -> shuffle
             .AddFanOutEdge(shuffler, [.. reducers])        // Shuffle -> many reducers
-            .AddFanInEdge([.. reducers], completion)       // All reducers -> completion
+            .AddFanInBarrierEdge([.. reducers], completion)       // All reducers -> completion
             .WithOutputFrom(completion)
             .Build();
     }

dotnet/samples/GettingStarted/Workflows/Observability/WorkflowAsAnAgent/WorkflowHelper.cs

@@ -25,7 +25,7 @@ internal static Workflow GetWorkflow(IChatClient chatClient, string sourceName)
         // Build the workflow by adding executors and connecting them
         return new WorkflowBuilder(startExecutor)
             .AddFanOutEdge(startExecutor, [frenchAgent, englishAgent])
-            .AddFanInEdge([frenchAgent, englishAgent], aggregationExecutor)
+            .AddFanInBarrierEdge([frenchAgent, englishAgent], aggregationExecutor)
             .WithOutputFrom(aggregationExecutor)
             .Build();
     }

dotnet/samples/GettingStarted/Workflows/SharedStates/Program.cs

@@ -27,7 +27,7 @@ private static async Task Main()
         // Build the workflow by connecting executors sequentially
         var workflow = new WorkflowBuilder(fileRead)
             .AddFanOutEdge(fileRead, [wordCount, paragraphCount])
-            .AddFanInEdge([wordCount, paragraphCount], aggregate)
+            .AddFanInBarrierEdge([wordCount, paragraphCount], aggregate)
             .WithOutputFrom(aggregate)
             .Build();
 

dotnet/src/Microsoft.Agents.AI.Workflows/AgentWorkflowBuilder.cs

@@ -135,7 +135,7 @@ private static Workflow BuildConcurrentCore(
 
         ExecutorBinding end = endFactory.BindExecutor(ConcurrentEndExecutor.ExecutorId);
 
-        builder.AddFanInEdge(accumulators, end);
+        builder.AddFanInBarrierEdge(accumulators, end);
 
         builder = builder.WithOutputFrom(end);
         if (workflowName is not null)

dotnet/src/Microsoft.Agents.AI.Workflows/WorkflowBuilder.cs

@@ -422,30 +422,26 @@ public WorkflowBuilder AddFanOutEdge<T>(ExecutorBinding source, IEnumerable<Exec
     }
 
     /// <summary>
-    /// Adds a fan-in edge to the workflow, connecting multiple source executors to a single target executor with an
-    /// optional trigger condition.
+    /// Adds a fan-in "barrier" edge to the workflow, connecting multiple source executors to a single target executor. Messages
+    /// will be held until every source executor has generated at least one message, then they will be streamed to the target
+    /// executor in the following step.
     /// </summary>
-    /// <remarks>This method establishes a fan-in relationship, allowing the target executor to be activated
-    /// based on the completion or state of multiple sources. The trigger parameter can be used to customize activation
-    /// behavior.</remarks>
     /// <param name="sources">One or more source executors that provide input to the target. Cannot be null or empty.</param>
     /// <param name="target">The target executor that receives input from the specified source executors. Cannot be null.</param>
     /// <returns>The current instance of <see cref="WorkflowBuilder"/>.</returns>
-    public WorkflowBuilder AddFanInEdge(IEnumerable<ExecutorBinding> sources, ExecutorBinding target)
-        => this.AddFanInEdge(sources, target, label: null);
+    public WorkflowBuilder AddFanInBarrierEdge(IEnumerable<ExecutorBinding> sources, ExecutorBinding target)
+        => this.AddFanInBarrierEdge(sources, target, label: null);
 
     /// <summary>
-    /// Adds a fan-in edge to the workflow, connecting multiple source executors to a single target executor with an
-    /// optional trigger condition.
+    /// Adds a fan-in "barrier" edge to the workflow, connecting multiple source executors to a single target executor. Messages
+    /// will be held until every source executor has generated at least one message, then they will be streamed to the target
+    /// executor in the following step.
     /// </summary>
-    /// <remarks>This method establishes a fan-in relationship, allowing the target executor to be activated
-    /// based on the completion or state of multiple sources. The trigger parameter can be used to customize activation
-    /// behavior.</remarks>
     /// <param name="sources">One or more source executors that provide input to the target. Cannot be null or empty.</param>
     /// <param name="target">The target executor that receives input from the specified source executors. Cannot be null.</param>
     /// <param name="label">An optional label for the edge. Will be used in visualizations.</param>
     /// <returns>The current instance of <see cref="WorkflowBuilder"/>.</returns>
-    public WorkflowBuilder AddFanInEdge(IEnumerable<ExecutorBinding> sources, ExecutorBinding target, string? label = null)
+    public WorkflowBuilder AddFanInBarrierEdge(IEnumerable<ExecutorBinding> sources, ExecutorBinding target, string? label = null)
     {
         Throw.IfNull(target);
         Throw.IfNull(sources);
@@ -472,10 +468,10 @@ public WorkflowBuilder AddFanInEdge(IEnumerable<ExecutorBinding> sources, Execut
         return this;
     }
 
-    /// <inheritdoc cref="AddFanInEdge(IEnumerable{ExecutorBinding}, ExecutorBinding)"/>
+    /// <inheritdoc cref="AddFanInBarrierEdge(IEnumerable{ExecutorBinding}, ExecutorBinding)"/>
     [Obsolete("Use AddFanInEdge(IEnumerable<ExecutorBinding>, ExecutorBinding) instead.")]
     public WorkflowBuilder AddFanInEdge(ExecutorBinding target, params IEnumerable<ExecutorBinding> sources)
-        => this.AddFanInEdge(sources, target);
+        => this.AddFanInBarrierEdge(sources, target);
 
     private void Validate(bool validateOrphans)
     {

dotnet/tests/Microsoft.Agents.AI.Workflows.UnitTests/WorkflowVisualizerTests.cs

@@ -114,7 +114,7 @@ public void Test_WorkflowViz_FanIn_EdgeGroup()
         // Build a connected workflow: start fans out to s1 and s2, which then fan-in to t
         var workflow = new WorkflowBuilder("start")
             .AddFanOutEdge(start, [s1, s2])
-            .AddFanInEdge([s1, s2], t)  // AddFanInEdge(target, sources)
+            .AddFanInBarrierEdge([s1, s2], t)  // AddFanInEdge(target, sources)
             .Build();
 
         var dotContent = workflow.ToDotString();
@@ -202,7 +202,7 @@ public void Test_WorkflowViz_Mixed_EdgeTypes()
         var workflow = new WorkflowBuilder("start")
             .AddEdge<string>(start, a, Condition) // Conditional edge
             .AddFanOutEdge(a, [b, c]) // Fan-out
-            .AddFanInEdge([b, c], end) // Fan-in - AddFanInEdge(target, sources)
+            .AddFanInBarrierEdge([b, c], end) // Fan-in - AddFanInEdge(target, sources)
             .Build();
 
         var dotContent = workflow.ToDotString();
@@ -310,7 +310,7 @@ public void Test_WorkflowViz_Mermaid_FanIn_EdgeGroup()
 
         var workflow = new WorkflowBuilder("start")
             .AddFanOutEdge(start, [s1, s2])
-            .AddFanInEdge([s1, s2], t)
+            .AddFanInBarrierEdge([s1, s2], t)
             .Build();
 
         var mermaidContent = workflow.ToMermaidString();
@@ -381,7 +381,7 @@ public void Test_WorkflowViz_Mermaid_Mixed_EdgeTypes()
         var workflow = new WorkflowBuilder("start")
             .AddEdge<string>(start, a, Condition) // Conditional edge
             .AddFanOutEdge(a, [b, c]) // Fan-out
-            .AddFanInEdge([b, c], end) // Fan-in
+            .AddFanInBarrierEdge([b, c], end) // Fan-in
             .Build();
 
         var mermaidContent = workflow.ToMermaidString();