Add RetryPolicy to ActivityHeartbeatingCancellation sample

src/ActivityHeartbeatingCancellation/README.md

@@ -16,4 +16,25 @@ Then in another terminal, run the workflow from this directory:
 
     dotnet run workflow
 
-This will show logs in the worker window of the workflow running.
+This will show logs in the worker window of the workflow running.
+
+# Retry + Heartbeat Activity Example
+
+This example demonstrates how to combine **Retry Policies** and **Activity Heartbeats**
+in Temporal's .NET SDK.
+
+## What This Sample Shows
+- How to configure retry settings for an activity.
+- How an activity can send heartbeat progress.
+- How Temporal detects stalled activities via `HeartbeatTimeout`.
+
+This pattern is useful for:
+- Batch processing
+- Migration jobs
+- Long-running operations
+- Resumable workflows
+
+## How to Run
+
+1. Start Temporal locally (`temporalite start`).
+2. Run the worker:

src/ActivityHeartbeatingCancellation/RetryAndHeartbeatActivity.cs

@@ -0,0 +1,19 @@
+using Temporalio.Activities;
+
+namespace RetryAndHeartbeat;
+
+public class RetryAndHeartbeatActivity
+{
+    [Activity]
+    public async Task<string> ProcessAsync(string input)
+    {
+        for (int i = 0; i < 5; i++)
+        {
+            // Send progress
+            ActivityExecutionContext.Current.Heartbeat(i);
+            await Task.Delay(500);
+        }
+
+        return $"Processed: {input}";
+    }
+}

src/ActivityHeartbeatingCancellation/RetryAndHeartbeatWorkflow.cs

@@ -0,0 +1,28 @@
+using Temporalio.Workflows;
+
+namespace RetryAndHeartbeat;
+
+[Workflow]
+public class RetryAndHeartbeatWorkflow
+{
+    [WorkflowRun]
+    public async Task<string> RunAsync(string input)
+    {
+        var options = new ActivityOptions
+        {
+            StartToCloseTimeout = TimeSpan.FromSeconds(30),
+            HeartbeatTimeout = TimeSpan.FromSeconds(5),
+            RetryPolicy = new()
+            {
+                MaximumAttempts = 3,
+                InitialInterval = TimeSpan.FromSeconds(1),
+                BackoffCoefficient = 2.0,
+                MaximumInterval = TimeSpan.FromSeconds(10)
+            }
+        };
+
+        return await Workflow.ExecuteActivityAsync(
+            (RetryAndHeartbeatActivity a) => a.ProcessAsync(input),
+            options);
+    }
+}